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Bridge Design Manual M 23-50
Washington State Department of Transportation
Bridge Design Manual M 23-50 Chapters 1-7
Washington State Department of Transportation Program Development Division Bridge and Structures
Persons with disabilities may request this information be prepared and supplied in alternate forms by calling the WSDOT ADA Accommodation Hotline collect (206) 389-2839. Persons with hearing impairments may access WA State Telecommunications Relay Service at TT 1-800-833-6388, Tele-Braille 1-800-833-6385, or Voice 1-800-833-6384, and ask to be connected to (360) 705-7097.
Engineering Publications Washington State Department of Transportation PO Box 47408 Olympia, WA 98504-7408 E-mail: [email protected] Phone: (360) 705-7430 Fax: (360) 705-6861 http://www.wsdot.wa.gov/fasc/EngineeringPublications/
Foreword
This manual has been prepared to provide Washington State Department of Transportation (WSDOT) bridge design engineers with a guide to the design criteria, analysis methods, and detailing procedures for the preparation of highway bridge and structure construction plans, specifications, and estimates. It is not intended to be a textbook on structural engineering. It is a guide to acceptable WSDOT practice. This manual does not cover all conceivable problems that may arise, but is intended to be sufficiently comprehensive to, along with sound engineering judgment, provide a safe guide for bridge engineering. A thorough knowledge of the contents of this manual is essential for a high degree of efficiency in the engineering of WSDOT highway structures. This loose leaf form of this manual facilitates modifications and additions. New provisions and revisions will be issued from time to time to keep this guide current. Suggestions for improvement and updating the manual are always welcome. All manual modifications must be approved by the Bridge Design Engineer.
__________________________________________ M. MYINT LWIN Bridge and Structures Engineer Washington State Department of Transportation
V:BDM1
September 1993
BRIDGE DESIGN MANUAL Criteria General Information
Contents Page
1.1 1.1.1 1.1.2 1.1.3
1.1.4
1.2 1.2.1 1.2.2
1.3 1.3.1
1.3.2
1.3.3 1.3.4 1.3.5
1.3.6
1.4 1.4.1
Manual Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Chapters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Numbering System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Revisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Manual Updates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Bridge Design Instruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Record of Manual Revisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bridge and Structures Office Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Organizational Elements of the Office . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Bridge and Structures Engineer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Bridge Design Engineer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Bridge Preservation Engineer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Bridge Management Engineer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Computer Applications Engineer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Consultant Coordinator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Architect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Staff Support Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. Office Administrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Procedures and Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design/Check Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. WSDOT PS&E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Consultant PS&E — Projects on WSDOT Right of Way . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Consultant PS&E — On County and City Right of Way Projects . . . . . . . . . . . . . . . . . . . . . . Design/Check Calculation File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. File of Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. To Be Included . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Not to Be Included . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Upon Completion of the Design Work, Fill Out a Design Completion Checklist . . . . . . . . . . Office Copy Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Addenda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shop Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Bridge Shop Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Sign Structure, Signal, and Illumination Shop Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contract Plan Changes (Change Orders and As-Builts) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Request for Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Processing Contract Revisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coordination With Other Divisions and Agencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preliminary Planning Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
August 1998
1 1 1 1 1 2 2 3 3 3 5 1.2-1 1 1 1 1 2 3 3 3 3 3 3 1.3-1 1 1 5 6 7 7 7 7 8 8 8 9 9 9 11 11 11 12 1.4-1 1
1.0-i
BRIDGE DESIGN MANUAL Criteria General Information 1.4.2
1.5 1.5.1 1.5.2 1.5.3
1.6 1.6.1 1.6.2 1.6.3 1.6.4 1.6.5 1.99
Contents
Final Design Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Coordination With Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Technical Design Matters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bridge Design Scheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preliminary Design Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Final Design Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Breakdown of Project Man-Hours Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Estimate Design Time Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Monthly Project Progress Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Guidelines for Bridge Site Visits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bridge Rehabilitation Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bridge Widenings and Seismic Retrofits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rail and Minor Expansion Joint Retrofits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . New Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bridge Demolition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 1 1 1.5-1 1 1 1 1 2 3 1.6-1 1 1 1 1 1 1.99-1
Appendix A — Design Aids 1.3-A1 Standard Design Criteria Form 1.3-A2 Exceptions to the Standard Design Criteria Form 1.3-A3 Design Completed Checklist 1.3-A4 Job File Table of Contents 1.3-A5 Office Time Report 1.3-A6 Not Included in Bridge Quantities List 1.3-A7 Special Provisions Checklist 1.5-A1 Breakdown of Project Manhours Required Form 1.5-A2 Monthly Project Progress Report Form
P:DP/BDM1 9807-0802
1.0-ii
August 1998
BRIDGE DESIGN MANUAL Criteria Structural Steel
Manual Description
1.1
Manual Description
1.1.1
Purpose This manual is intended to be a guide for Bridge Designers and others involved with bridge design for the Washington State Department of Transportation (WSDOT). It contains design details and methods that have been standardized and it interprets the intent of specifications. It is not intended to govern design in unusual situations nor to unduly inhibit the designer in the exercise of engineering judgment. There is no substitute for good judgment. The following axioms are given as a reminder that simple things make a big difference. 1.
Gravity always works — if something is not supported, it will fall.
2.
A chain reaction will cause small failures to become big failures, unless alternate load paths are available in the structure (i.e., progressive collapse).
3.
Small errors, such as a drafting error or a misplaced decimal, can cause large failures.
4.
Vigilance is needed to avoid small errors. This applies to construction inspection as well as in the design phase.
5.
A construction job should be run by one person with authority, not a committee. It has been said that a camel is a horse designed and built by a committee.
6.
High quality craftsmanship must be provided by everyone.
7.
An unbuildable design is not buildable. An obvious fact often overlooked by the architect or structural designer. Think about how forms will be built, then removed if necessary.
8.
There is no foolproof design.
9.
The best way to ensure a failure is to disregard or ignore lessons from past failures.
10. Many problems can be avoided by using a little loving care.
1.1.2
Specifications The AASHTO publications Standard Specifications for Highway Bridges and LRFD Bridge Design Specifications are the basic documents guiding the design of highway bridges and structures. This WSDOT Bridge Design Manual is intended to supplement AASHTO and other specifications by providing additional direction, design aids, examples, and information on office practices. Where conflicts exist between this manual and the AASHTO Standard Specifications, this manual will control. When a conflict exists that is not resolved within the manual, further guidance shall be obtained from the Bridge Design Engineer or his representative. The AASHTO publications are not duplicated in this manual. Appropriate specifications and other references are listed in Section 1.99.
1.1.3
Format A. General The Bridge Design Manual consists of two volumes with each chapter organized as follows: Criteria or other information Appendix A (printed on yellow paper) Design Aids Appendix B (printed on salmon paper) Design Examples
August 1998
1.1-1
BRIDGE DESIGN MANUAL Criteria Structural Steel
Manual Description
B. Chapters 1.
General Information
2.
Preliminary Design
3.
Analysis
4.
Loads
5.
Reinforced Concrete Superstructures
6.
Prestressed Concrete Superstructures
7.
Structural Steel
8.
Miscellaneous Design
9.
Substructure Design
10. Detailing Practice 11. Quantities 12. Construction Costs 13. Construction Specifications 14. Inspection and Rating C. Numbering System 1.
The numbering system for the criteria consists of a set of numbers followed by letters as required to designate individual subjects. This format is similar to that used by AASHTO. Example: 5.0
Reinforced Concrete Superstructures
(Chapter)
5.4
Box Girder Bridges
(Section)
5.4.2
Girder
(Subsection)
C. Shear Resistance 1.
The Shear Diagram a.
Shear Reinforcement (1) Placement
2.
Numbering of Sheets Each section starts a new page numbering sequence. The page numbers are located in the lower outside corners and begin with the chapter number, followed by the section number, then a sequential page number. Example: 5.4-1, 5.4-2, etc.
1.1-2
August 1998
BRIDGE DESIGN MANUAL Criteria Structural Steel 3.
Manual Description Appendices are included to provide the designer with design aids (Appendix A) and examples (Appendix B). Design aids are generally standard in nature, whereas examples are modified to meet specific job requirements. An appendix is numbered using the chapter followed by section number and then a hyphen and the letter of the appendix followed by consecutive numbers. Example: 5.4-A1 (Box Girder Bridges) designates a design aid required or useful to accomplish the work described in Chapter 5, Section 4.
4.
Numbering of Tables and Figures Tables and figures shall be numbered using the chapter, section, subsection in which they are located, and then a hyphen followed by consecutive numbers.
Example: Figure 5.4.2-1 is the first figure found in Chapter 5, section 4, subsection 2.
1.1.4
Revisions A. Manual Updates The Bridge Design Manual will change as new material is added and as criteria and specifications change. Revisions and new material will be issued with a Publications Transmittal Form. The form will have a revision number and remarks or special instructions regarding the sheets. The revision number shall be entered on the Record of Revision sheet in this manual. This allows the user to verify that the manual is up to date. B. Bridge Design Instruction Special instructions regarding interpretation of criteria or other policy statements may be issued using a Bridge Design Instruction (BDI). The BDI will be transmitted in the same manner as outlined above for manual revisions. The BDI should be inserted in the appropriate place in the manual and remains in effect until the expiration date shown or until superseded by a revision to the manual. A sample BDI is shown on Figure 1.1.4-1.
P:DP/BDM1 9807-0802
August 1998
1.1-3
BRIDGE DESIGN MANUAL Criteria Structural Steel
Manual Description
February 1997
BRIDGE DESIGN INSTRUCTION 5.1.1 CHAPTER 5 SUBJECT:
Use of Concrete Class 5000 and Class 4000D
ACTION:
Place this instruction in your manual and note the instruction number in your Record of Manual Revisions, 1.1.4.
TEXT
There is confusion regarding the availability of Concrete Class 5000. This class of concrete is available within a 30-mile radius of Seattle, Spokane and Vancouver, Washington. “Available” means that there are concrete suppliers in these urban areas capable of supplying Concrete Class 5000 in accordance with WSDOT specifications. Outside this 30-mile radius (or near the fringe), the concrete suppliers generally do not have the quality control procedures and expertise to supply this higher strength concrete. The Construction Office or Materials Lab should be contacted for availability for project sites outside these areas. In general, Class 4000D Concrete would be specified for bridge roadway decks outside this 30 mile radius. Class 4000D Concrete specifications require a 14-day wet cure and flyash as an additive. Typically, Class 4000 Concrete would be specified for other bridge concrete members above ground. This mix was developed by the Materials Lab to be at least as durable as Class 5000 Concrete. By utilizing the above guidelines, WSDOT will receive the most durable bridge deck at the least cost.
Approved: _________________________ C. C. Ruth Bridge Design Engineer CCR/db RTS
Figure 1.1.4-1
1.1-4
August 1998
BRIDGE DESIGN MANUAL Criteria Structural Steel
Manual Description
C. Record of Manual Revisions In order that a ready means be available to check whether a manual is up to date, each manual holder is requested to keep his copy up to date and to record Bridge Design Instructions or Revisions as material is added or changed. The form below is intended for use in keeping this record. At any time, a manual holder will be able to check his list with the list in the “master” manual.
Revision Number
August 1998
Entry Date
By (Initial)
Revision Number
Entry Date
By (Initial)
Revision Number
Entry Date
By (Initial)
1.1-5
BRIDGE DESIGN MANUAL Criteria General Information 1.2
Bridge and Structures Office Organization
1.2.1
General
Bridge and Structures Office Organization
The document defining the responsibilities for bridge design within the Washington State Department of Transportation (WSDOT) is the Organization Handbook. In that document, the responsibilities of the Bridge and Structures Office are stated as follows: Provides structural engineering services for the department. Provides technical advice and assistance to other governmental agencies on such matters. The WSDOT Design Manual states the following: Bridge design is the responsibility of the Bridge and Structures Office in Olympia. Any design authorized to be performed at the regional level is subject to review and approval by the Bridge and Structures Office.
1.2.2
Organizational Elements of the Office A. Bridge and Structures Engineer Responsible for structural engineering services for the department. Manages staff and programs for structure design, contract plan preparation, and inspections and assessments of existing bridges. B. Bridge Design Engineer The Bridge Design Engineer is directly responsible to the Bridge and Structures Engineer for structural design and review, and advises other divisions and agencies on such matters. 1.
Structural Design Units The Structural Design Units are responsible for the final design of bridges and other structures. Final design includes preparation of plans. The units provide special design studies, develop design criteria, check shop plans, and review designs submitted by consultants. Each design unit normally consists of individuals including a section supervisor and a bridge specialist. Organization and job assignments within the unit are flexible and are related to the projects underway at any particular time as well as to the qualifications of individuals. The emphasis in the design sections is on providing sound designs, checking, reviewing, and detailing in an efficient manner. A bridge specialist is assigned to each design unit. Each specialist has a particular area of responsibility. The three areas are concrete, steel, and expansion joints and bearings. The specialist acts as a resource person for the bridge office in his specialty and is responsible for keeping up-to-date on current AASHTO criteria, new design concepts, technical publications, construction and maintenance issues. The design units are also responsible for the design and preparation of contract plans for modifications to bridges in service. These include bridge rail replacement, deck repair, seismic retrofits, emergency repairs when bridges are damaged by vehicle or ship collision or natural phenomenon, and expansion joint and drainage retrofit. They review proposed plans of utility attachments to existing bridges.
August 1998
1.2-1
BRIDGE DESIGN MANUAL Criteria General Information 2.
Bridge and Structures Office Organization
Bridge Projects Unit The Bridge Projects Engineer directs preliminary design work, specification and cost estimates preparation, falsework review, and coordinates scheduling of bridge design projects with the Bridge Design Engineer and the Design Unit Supervisors. The Preliminary Design engineers are responsible for bridge project planning from design studies to preliminary project reports. They are responsible for preliminary plan preparation of bridge and walls including assembly and analysis of site data, preliminary structural analysis, cost analysis, determination of structure type, and drawing preparation. They also review highway project environmental documents and design reports and handle Coast Guard liaison duties. The Specifications and Estimate (S&E) engineers develop and maintain construction specifications and cost estimates for bridge projects originating in the Bridge and Structures Office. They also review the specifications and cost estimates for bridge contracts prepared by consultants and other government agencies which are administered by WSDOT. They assemble and review the completed bridge PS&E before submittal to the Plans Branch. They also coordinate the PS&E preparation with the regions, Plans Branch, and maintain bridge construction cost records. The Construction Support engineers are responsible for checking the contractor’s falsework, shoring, and form plans. Shop plans review and approval are coordinated with the design sections. Actual check of the shop plan is done in the design section. Field requests for plan changes come through this office for a recommendation as to approval. As built plans are prepared by this unit at the completion of a contract. The Scheduling Engineer monitors the design work schedule for the Bridge and Structures Office and maintains records of bridge contract costs. In addition, the unit is responsible for the Bridge Design Manual, design standards, professional activities, and AASHTO support.
C. Bridge Preservation Engineer Directs activities and develops programs to assure the structural and functional integrity of all state bridges in service. Directs emergency response services when bridges are damaged. 1.
Bridge Preservation Unit The Bridge Preservation Unit is responsible for planning and implementation of an inspection program for the more than 3,000 fixed and movable state highway bridges. In addition, the unit provides inspection services on some local agency bridges and on the state’s 21 ferry terminals. All inspections are conducted in accordance with the National Bridge Inspection Standards (NBIS). The unit maintains a statewide computer inventory Washington State Bridge Inventory System (WSBIS), of current information on more than 7,300 state, county, and city bridges in accordance with the NBIS. This includes load ratings for all bridges. It prepares a Bridge List of the state’s bridges which is published every two years. The unit is responsible for the bridge load rating and risk reduction (SCOUR) programs. It provides damage assessments and emergency response services when bridges are damaged or lost due to vehicle or ship collision or natural phenomenon such as floods, wind, or earthquakes.
1.2-2
August 1998
BRIDGE DESIGN MANUAL Criteria General Information
Bridge and Structures Office Organization
D. Bridge Management Engineer This Bridge Management Unit is responsible for program development, planning, and monitoring of all H-Program activities. These include HBRRP funded bridge replacements and rehabilitation, bridge deck protection, major bridge repair, and bridge painting. In addition, this unit manages the bridge deck protection program including the deck testing program and the bridge research program. It is responsible for the planning, development, coordination, and implementation of new programs (e.g., Seismic Retrofit and Preventative Maintenance), experimental feature projects, new product evaluation, and technology transfer. E. Computer Applications Engineer The Computer Support Unit is responsible for computer resource planning and implementation, computer user support, liaison with Management Information Systems (MIS), and computer aided engineer operation support. In addition, the unit is responsible for Standard Plan updates. F. Consultant Coordinator The Consultant Coordinator prepares bridge consultant agreements and coordinates consultant PS&E development activities with those of the department. G. Architect The Principal Architect is responsible for approving preliminary plans, preparing renderings, model making, and other duties to improve the aesthetics of our bridges and other structures. The Principal Architect works closely with staff and regions. During the design phase, designers should get the Architect’s approval for any changes to architectural details shown on the approved preliminary plan. H. Staff Support Unit The Staff Support Unit is responsible for many support functions, such as: typing, timekeeping, payroll, receptionist, vehicle management, mail, inventory management, and other duties requested by the Bridge and Structures Engineer. Other duties include: of field data, plans for bridges under contract or constructed, and design calculations. This unit also maintains office supplies and provides other services. I.
Office Administrator The Office Administrator is responsible for coordinating personnel actions, updating the organizational chart, ordering technical materials, and other duties requested by the Bridge and Structures Engineer. Staff development and training are coordinated through the Office Administrator. Logistical support, office and building maintenance issues are also handled by the Office Administrator.
July 2000
1.2-3
BRIDGE DESIGN MANUAL Criteria General Information 1.2.3
Bridge and Structures Office Organization
Design Unit Responsibilities and Expertise The following is an updated summary of design responsibilities/expertise within the Bridge Design Section. Contact the unit manager for the name of the appropriate staff expert for the needed specialty. Unit Manager
Responsibility/Expertise
K. N. Kirker
Expansion Joint Modifications Retaining Walls (including MSE, Tie-Back, and Soil Nail) Seismic Retrofit
Y. A. Mhatre
Noise Walls Bridge Traffic Barriers Standard Plans for Prestressed Concrete
R. T. Shaefer
Coast Guard Permits Cost Estimates Standard Plans (other than Prestressed Concrete) Bridge Design Manual
J. A. VanLund
Sign Supports, Light Standards, Traffic Signal Supports Repairs to Damaged Prestressed Girder Bridges
P. T. Clarke
Floating Bridges Special Structures
P65:DP/BDM1
1.2-4
July 2000
BRIDGE DESIGN MANUAL Criteria General Information
Design Procedures and Processes
1.3
Quality Control/Quality Assurance (QC/QA) Process for WSDOT Bridge Designs
1.3.0
General A. The QA/QC process for bridge designs is a critical element of quality structure plan preparation. The overall goals of the structural design process are: • The structural design maximizes the safety of the traveling public and is in accordance with State Law. • The structural design is in accordance with the WSDOT Bridge Design Manual, AASHTO Bridge Design Specifications, good structural engineering practice, and geometric criteria provided by the Region. • Designed structures are durable, low-maintenance, and inspectable. • The structural design facilitates constructibility and minimizes overall construction costs, while exhibiting a pleasing architectural style. • The structural design contract documents are produced in accordance with customer’s needs (schedule, construction staging, and available program funding). • Structural design costs are minimized. • A well-organized and readable structure calculation record is produced. • Plan quality is maximized. • Design process allows for change, innovation, and continuous improvement. The overall goals are listed in order of importance. If there is a conflict between goals, the more important goal takes precedence. The design unit manager determines project assignments and the QC/QA process to be used in preparation of the structural design. The intent of the QC/QA process is to facilitate production efficiency and cost-effectiveness while assuring the structural integrity of the design and maximizing the quality of the structure contract documents.
1.3.1
Design/Check Procedures A. PS&E Prepared by WSDOT Bridge and Structures Office 1.
Design Team The design team, consisting of the Designer(s), Checker(s), Structural Detailer(s), and Specification and Estimate engineer are responsible for preparing a set of contractible, clear, and concise structural contract documents by the scheduled date and within the workforce hours allotted for the project. On large projects, the design unit manager may assign a designer additional duties as a Design Team Leader to assist the manager in planning, coordinating, and monitoring the activities of the design team. In this case, the team leader would also coordinate with the Region and the Geotechnical Branch. The QC/QA process will likely vary depending on the type and complexity of the structure being designed, and the experience level of the design team members. More supervision, review, and checking are required when the design team members are less experienced. In general, it is good QC/QA practice to have some experienced members on each design team. All design team members should have the opportunity to provide input for maximizing the quality of the design being produced.
July 2000
1.3-1
BRIDGE DESIGN MANUAL Criteria General Information 2.
Design Procedures and Processes
Designer Responsibility The designer is responsible for the structural analysis, completeness, correctness, and quality of the plans. The designer shall provide quality control in the process of plan preparation. That is, errors and omissions need to be caught and corrected before subsequent checking and review of plans. A good set of example plans to follow, representative of bridge type, is indispensable in this regard. During the design phase of a project, the designer will need to communicate with other stakeholders. This includes acquiring, finalizing or revising roadway geometrics, soil reports, hydraulics recommendations, and utility requirements. Constructibility issues may also require that the designer communicate with the Region or Construction Office. The bridge plans must be coordinated with the PS&E packages produced concurrently by the Region. The designer or team leader is responsible for project planning which involves the following: a.
Prepare a Design Time Estimate Bar Chart (see Section 1.5.2).
b.
Identify tasks and plan order of work.
c.
Prepare design criteria, which should be included in the design calculations. Use Standard Design Criteria Form, 1.3-A1-1 for routine projects. A project specific design criteria should be made when appropriate. Compare tasks with BDM office practice and AASHTO bridge design specifications. (1) Sufficient guidelines? (2) Deviation from BDM/AASHTO? (3) Any question on design approach? (4) Deviation from office practices regarding design and details? (5) Other differences.
d.
Meet with the Region design staff and other project stakeholders early in the design process to resolve as many issues as possible before proceeding with final design and detailing.
e.
Identify coordination needs with other designers, units, and offices.
f.
Early in the project, determine the number and titles of sheets. For projects with multiple bridges, each set of bridge sheets should have a unique set of bridge sheet numbers. The bridge sheet numbering system should be coordinated with the Region design staff.
g.
At least monthly or as directed by the design unit manager: (1) Update Project Schedule and List of Sheets. (2) Estimate percent complete. (3) Estimate time to complete. (4) Work with design unit manager to adjust resources, if necessary.
h.
1.3-2
Develop preliminary quantities for 90 percent complete cost estimate.
July 2000
BRIDGE DESIGN MANUAL Criteria General Information i.
Design Procedures and Processes
Near end of project: (1) Keep track of sheets as they are completed. (2) Develop quantities and special provisions checklists that are to be turned in with the plans. (3) Prepare Bar List. (4) Enter information into the Bridge Design Record. (5) Coordinate all final changes, including review comments from the checker, managers, specialists, the Region, and the Construction Office. (6) Meet with Region design staff and other project stakeholders at the constructibility meeting to address final project coordination issues. The designer shall advise and get the design unit manager’s approval whenever details deviate from the BDM office practice and AASHTO Bridge Design Specifications. The designer shall provide documentation of the structural design deviations in the calculations. The designer should inform the design unit manager of any areas of the design which should receive special attention during checking and review. The design calculations are prepared by the designer and become a very important record document. Design calculations will be a reference document during the construction of the structure and throughout the life of the structure. It is critical that the design calculations be user friendly. The design calculations shall be well organized, clear, properly referenced, and include numbered pages along with a table of contents. The design calculations shall be archived. Computer files should be archived for use during construction, in the event that changed conditions arise. Archive-ready design and check calculations shall be bound and submitted to the design unit manager within 30 days of submitting the 100 percent PS&E. Calculations shall be stored in the design unit until completion of construction. After construction, they shall be sent to archives. The designer is also responsible for resolving construction problems referred to the Bridge Office during the life of the contract. These issues will generally be referred through the Bridge Technical Advisor, the design unit manager, the Construction Support Unit, or the OSC Construction Unit.
3.
Design Checker Responsibility The checker is responsible to the design unit manager for “quality assurance” of the structural design, which includes checking the design and plans to assure accuracy and constructibility. The design unit manager works with the checker to establish the level of checking. The checking procedure for assuring the quality of the design will vary from project to project. Following are some general checking guidelines: a.
Design Calculations (1) For designs checked by an experienced checker, a review and initialing of the designer’s calculations by the checker is acceptable. If it is more efficient, the checker may choose to perform his/her own calculations to check. All the designer and checker calculations shall be placed in one design calculation set.
July 2000
1.3-3
BRIDGE DESIGN MANUAL Criteria General Information
Design Procedures and Processes
(2) For designs checked by an inexperienced checker, a more thorough check should be performed by the checker to enhance his/her understanding of structural design. In this case, the design unit manager should provide the checker with a design example. (3) Revision of design calculations, if required, is the responsibility of the designer. b.
Structural Plans (1) The checker’s plan review comments are recorded on the structural plans, including details and bar lists, and returned to the designer for consideration. If the checker’s comments are not incorporated, the designer should provide justification for not doing so. If there is a difference of opinion that cannot be resolved between the designer and checker, the unit manager shall resolve the issue. (2) If assigned by the design unit manager, the checker shall perform a complete check of the geometry using CADD, hand calculations, or a geometric program. (3) Revision of plans, if required, is the responsibility of the designer.
4.
Structural Detailer Responsibility The structural detailer is responsible for the structural plan sheets. The plans shall be neat, correct, and easy to follow and drawn to scale. The structural detailer may also assist the designer and design checker in such areas as determining control dimensions and elevations, geometry, and calculating quantities. Some detailing basics and principles:
1.3-4
a.
Refer to BDM, Chapter 10, for detailing practices.
b.
Provide necessary and adequate information. Try to avoid repetition of information.
c.
Avoid placing too much information into any one sheet.
d.
Plan sheets should detailed in a consistent manner and follow accepted detailing practices.
e.
Provide clear and separate detail of structural geometrics. Use clear detailing such as “stand alone” cross sections or a framing plan to define the structure.
f.
Avoid reinforcing steel congestion.
g.
Check reinforcement detail for consistency. Beware of common mistakes about placement of stirrups and ties (such as: stirrups too short, effect of skew neglected, epoxy coating not considered, etc.). Check splice location and detail, and welding locations.
h.
Use cross references properly.
i.
Use correct and consistent terminology. For example, the designation of Sections, Views, and Details.
j.
Check for proper grammar and spelling.
k.
On multiple bridge contracts, the structural detailing of all bridges within the contract shall be coordinated to maximize consistency of detailing from bridge to bridge. Extra effort will be required to assure uniformity of details, particularly if multiple design units and/or consultants are involved in preparing bridge plans. This is a critical element of good quality bridge plans.
July 2000
BRIDGE DESIGN MANUAL Criteria General Information l. 5.
Design Procedures and Processes
Refer to the Bridge Book of Knowledge for current special features and details used on other projects.
Specialist Responsibility There are currently four specialist positions in the Bridge and Structures Office. There is a specialist assigned to each of the three design sections and one to the Bridge Preservation Section. The primary responsibility of the specialist is to act as a knowledge resource for this office. The Specialists maintain an active knowledge of their specialty area along with a current file of products and design procedures. Proactive industry contacts are maintained by the Specialists. Specialists also provide training in their area of specialty. As contract plans are prepared by other designers, the Specialists are expected to review and initial drawings covered by their specialty area. Plans produced directly by Specialists in their specialty area should be prepared with their own stamp and signature. Specialists also assist the Bridge Engineer in reviewing and voting on amendments to AASHTO specifications. They also are responsible for keeping their respective chapters of the Bridge Design Manual up to date. The secondary responsibility of the Specialist is to serve as design section supervisor when the supervisor is absent. There are three specialty areas in the Design Section: Concrete, Expansion Joints and Bearings, and Steel.
6.
Design Unit Technical Responsibilities Each Design Unit is responsible for maintaining a resource of technical knowledge and leadership. As described in the previous Section (5.), each unit has a Design Specialist (Concrete, Steel, Expansion Joints and Bearings). In addition, each Design Unit maintains a resource of technical knowledge in several technical areas. Following, is a list of all technical subjects for which a resource is maintained: • Coast Guard Permits • Cost Estimates • Bridge Special Provisions • Sign Supports, Light Standards, Traffic Signal Supports • Repairs to Damaged Prestressed Girders • Expansion Joint Modifications • Retaining Walls (Including MSE, Tie-Back, and Soil Nail) • Seismic Retrofit • Noise Walls • Traffic Barrier Retrofits/Standards • Bridge Standard Plans (BDM) The resource/leadership responsibility for these technical areas does not necessarily include responsibility for performing all of the work relating to the technical area. For many of the technical areas, the Design Unit acts as a resource for the technical area, only, and as a contact for industry and stakeholders.
July 2000
1.3-5
BRIDGE DESIGN MANUAL Criteria General Information 7.
Design Procedures and Processes
Specification and Estimating Engineer Responsibilities The S&E Engineer is responsible for compiling the PS&E package for bridge and/or related highway structural components. This PS&E package includes Special Provisions (BSPs and GSPs as appropriate), construction cost estimate, construction working day schedule, test hole boring logs and other appendices as appropriate, and the design plan package. The S&E Engineer begins work after the design unit submits copies of the 90 percent design plans. This normally occurs on or before the date specified in the Bridge Design Schedule. A set of quantities, a copy of the “Not Included in Bridge Quantities,” and a S&E Checklist are included in the PS&E package. As a first order of business, the S&E Engineer distributes the 90 percent design plans for review by the Region and other offices. While other offices are reviewing the plan package, the S&E Engineer attends to the following duties. • Review the job file, foundation report, and design plans to make sure that materials specified in the plans are consistent with the current Standard Specifications. • Check the plans for engineering accuracy, completeness, and constructibility. • Create a run list of BSPs, GSPs, and appropriate Standard Specification amendments. • Compile a cost estimate file using the quantities submitted by the designers and current Unit Cost figures for the various materials used in the bridge. • The S&E Engineer develops a construction working day schedule which is also based on the quantities submitted by the designers. At the same time, the S&E Engineer coordinates the Bridge and Structures Office review of the Review PS&E and responds with comments to the Region. The S&E Engineer also receives all Region review comments and distributes them to the appropriate designer for action. The S&E Engineer also participates in the Region Review Roundtable Meeting. After the Review Roundtable Meeting, all comments are addressed by the designers. The S&E Engineer has the following responsibilities during coordination of the Final Bridge PS&E turn in. • Make Special Provision reviews to the Bridge Special Provision word file. • Inform the appropriate Region PS&E contact when the word file is complete and ready for transfer. • Complete Cost Estimate and Quantity revisions to the cost estimate files. • Electronically distribute all cost estimate file revisions to the appropriate Region PS&E contact. Once the final Bridge Sheet mylars are printed, stamped, and signed, the S&E Engineer arranges for 11 by 17 paper prints for submittal to the appropriate Region PS&E contact. The original stamped and signed mylars are turned in to the Construction Plans Unit for storage. During the Advertising period many questions are funneled into the Bridge Office by the Project Engineers and the communications are generally distributed to the S&E Engineer. The S&E Engineer will ascertain the query, answer the question from the Contractors, or seek advice or help from the design engineer. The S&E Engineer will then respond back to the PE. Revisions to the Plans or Specs are sometimes needed as a result of these questions from Contractors.
1.3-6
July 2000
BRIDGE DESIGN MANUAL Criteria General Information
Design Procedures and Processes
Addendum’s are created to augment the original advertised document to make sure all Contractors are advised prior to Bid Openings. These Addendum’s are coordinated with the Region and OSC Plans. The S&E Engineer attends the award meetings to justify bids and advise whether or not to award the contract. Other responsibilities included are: • Special Provisions and Estimates for Change Order Work • Cost estimates in the scoping stage of a project • Working Day information during Stage Construction planning • Initiates/Coordinates Amendment and GSP Updates • Maintains BSP Library 8.
Design Unit Manager Responsibility a.
The design unit manager is responsible to the Bridge Design Engineer for the timely completion and quality of the bridge plans.
b.
The design unit manager works closely with the design team (designer, checker, and structural detailer) during the design and plan preparation phases to help avoid major changes late in the design process. Activities during the course of design include: (1) Evaluate the complexity of the project and the designer’s skill and classification level to deliver the project in a timely manner. Determine both the degree of supervision necessary for the designer and the amount of checking that will be required by the checker. (2) Assist the design team in defining the scope of the project, identifying the tasks to be accomplished, developing a project work plan and schedule, and assigning resources to achieve delivery of the project. (3) Review and approve design criteria before start of design. (4) Help lead designer conduct face-to-face project meetings, such as: project “kick-off” and “wrap-up” meetings with Region, geotechnical staff, bridge construction, and consultants to resolve outstanding issues. (5) Assist the design team with planning, anticipating possible problems, collectively identifying solutions, and facilitating timely delivery of needed information, such as geometrics, hydraulics, foundation information, etc. (6) Interact with design team regularly to discuss progress, problems, schedule, analysis techniques, constructibility and design issues. Always encourage forward thinking, innovative ideas and suggestions for quality improvement. (7) Arrange for and provide the necessary resources and tools for the design team to do the job right the first time. Offer assistance to help resolve questions or problems. (8) Help document and disseminate information on special features and lessons learned for the benefit of others and future projects.
July 2000
1.3-7
BRIDGE DESIGN MANUAL Criteria General Information
Design Procedures and Processes
(9) Mentor and train designers and detailers on state-of-the-art practices and through the assignment of a variety of structure types. c.
The design unit manager works closely with the design team during the plan review phase. Review efforts should concentrate on reviewing the completed plan details and design calculations for completeness and for agreement with office criteria and practices. Review the following periodically and at the end of the project: (1) Design Criteria • Seismic “a” value • Foundation report recommendations, selection of alternates • Deviations from AASHTO, BDM, Documentation (2) Design Time
d.
Review designer’s estimated time to complete the project. Plan resource allocation to complete the project to meet the scheduled Ad Date. Monitor monthly time spent on the project. Prepare and submit to the Bridge Projects Engineer monthly time reports for each project. Estimate time remaining to complete project, percent completed, and whether project is on or behind schedule. Arrange and plan resources to ensure a timely delivery of the project within the estimated time to complete the project.
e.
Advise Region of project scope and cost-creep. Use quarterly status reports to update Region and Bridge Projects Engineer.
f.
Use appropriate computer scheduling software or other means to monitor time usage and to allocate resources and to plan projects.
g.
Fill out Office Time Report (see Appendix 1.3-A5).
h.
Review of constructibility. Any problems unique to the project?
i.
Check the final plans for the following: (1) Scan the job file for unusual items relating to geometrics, hydraulics, geotechnical, environmental, etc. (2) Overall check/review of sheet #1, the bridge layout for: • Consistency — especially for multiple bridge project • Missing information (3) Check footing layout for conformance to Bridge Plan and for adequacy of information given. Generally, the field personnel should be given enough information to “layout” the footings on the ground without referring to any other sheets. Details should be clear, precise, and dimensions tied to base reference such as survey line or defined center line of bridge. (4) Check the sequence of the plan sheets. They should adhere to the following order: layout, footing layout, substructures, superstructures, miscellaneous details, barriers, and bar list. Also check for appropriateness of the titles.
1.3-8
July 2000
BRIDGE DESIGN MANUAL Criteria General Information
Design Procedures and Processes
(5) Check overall dimensions and elevations, spot check for compatibility. For example, check compatibility between superstructures and substructure. Also spot check bar marks. (6) Use one’s training, common sense, and experience to “size-up” structural dimensions and reinforcement, etc., for structural adequacy. When in doubt, prepare for a line of questioning to the designer/checker. j. 9.
Stamp and seal the plans.
Bridge Design Engineer’s Responsibilities The Bridge Design Engineer is the coach, mentor, and facilitator for the WSDOT QC/QA Bridge Design Process. The leadership and support provided by this position is a major influence in assuring bridge design quality for structural designs performed by both WSDOT and consultants. The following summarizes the responsibilities of the Bridge Design Engineer relative to QC/QA: a.
When the structural contract plans are sealed by the Bridge Design Engineer, a structural/ constructibility review of the plans is performed. This is a quality assurance (QA) function as well as meeting the “responsible charge” requirements of the laws relating to Professional Engineers.
b.
Review and approve the Preliminary Bridge Plans. The primary focus for this responsibility is to assure that the most cost-effective and appropriate structure type is selected for a particular bridge site.
c.
Participate in coordination, scheduling, and project-related discussions with stakeholders, customers, and outside agencies relating to major structural design issues.
d.
Facilitate resolution of major project design issues.
e.
Review unique project special provisions and major Standard Specification modifications relating to structures.
f.
Facilitate partnerships between WSDOT, consultant, and construction industry stakeholders to facilitate design quality.
g.
Encourage designer creativity and innovation.
h.
Exercise leadership and direction for maintaining a progressive and up to date Bridge Design Manual.
i.
Create an open and supportive office environment in which Design Section staff are empowered to do high quality structural design work.
10. General Bridge Plan Signature Policy The sealing and signature of bridge plans is an important element of the Bridge QC/QA process. It signifies review and responsible charge of the design and details represented in the plans. The Bridge and Structures Office intends to have at least one Licensed Structural Engineer seal and sign each contract plan sheet (except the bar list). For major projects, the Design Unit Manager and the Bridge Design Engineer will typically review, seal, and sign the bridge plans. For routine bridge designs and transportation structure designs, the Design Unit Manager (SE License) and designer with a Civil Engineer License will typically review, seal, and sign the contract plans (except the bar list).
July 2000
1.3-9
BRIDGE DESIGN MANUAL Criteria General Information
Design Procedures and Processes
B. PS&E Prepared by Consultant This section is yet to be developed, but it will include the following elements: • Consultant Coordinator Responsibilities Scope of Work Negotiate Contract (Task Assignments) Coordinate/Negotiate Changes to Scope of Work • WSDOT Design Reviewer/Coordinator Responsibilities Review consultant’s design criteria and standard details early in the project Identify resources needed to complete work Early agreement on structural concepts/design method to be used Identify who is responsible for what Monitor progress Facilitate communication Review for design consistency with WSDOT practices and other bridge designs in project Resolve differences Assure that consultant’s QC/QA plan was followed during design • Design Unit Manager Responsibilities Encourage/Facilitate communication Early involvement to assure that design concepts are appropriate Empower Design Reviewer/Coordinator Facilitate resolution of problems beyond ability of Reviewer/Coordinator • S&E Unit Responsibilities Prepare Specials and Estimate based on Consultant’s special provision checklist and quantities Review plans for consistency Forward Special Provisions and Estimate to consultant for review and comment • Bridge Design Engineer Responsibilities Cursory review of design plans Signature approval of S&E bridge contract package C. Consultant PS&E — On County and City Right of Way Projects Consultants are frequently used by counties and cities to design bridges. The Highways and Local Programs Office determines which projects are to be reviewed by the Bridge and Structures Office. Where a review is required, the PS&E is sent by Highways and Local Programs to the Bridge Projects Engineer for assignment. The Bridge and Structures Office Consultant Coordinator does not become involved. A Review Engineer will be assigned to the project and will review the project as outlined for Consultant PS&E — Projects on WSDOT Right of Way (see Section 1.3.1.B). The plans with the reviewers’ comments should be returned to the Bridge Projects Unit where the comments will be transferred to a second set of plans which will be returned to Highways and Local Programs. The original set will be filed in the Bridge Projects Unit.
1.3-10
July 2000
BRIDGE DESIGN MANUAL Criteria General Information
Design Procedures and Processes
Review is made of the Preliminary Plan first and the PS&E second. Comments are treated as advisory, although major structural problems must be corrected. An engineer from the county, city, or consultant may contact the reviewer to discuss the comments.
1.3.2
Design/Check Calculation File A. File of Calculations The Bridge and Structures Office maintains a file of all pertinent design/check calculations for documentation and future reference. B. Procedures After an assigned project is completed and the bridge is built, the designer should turn in to the manager a bound file containing the design/check calculations. C. File Inclusions The following items should be included in the file: 1.
Index Sheets Number all calculation sheets and prepare an index by subject with the corresponding sheet numbers. List the name of the project, SR Number, designer/checker initials, date (month, day, and year), and supervisor’s initials.
2.
Design Calculations These should include design criteria, loadings, structural analysis, one set of moment and shear diagrams and pertinent computer input and output data (reduced to 8 1 2 inch by 11 inch sheet size).
3.
Special Design Features Brief narrative of major design decisions or revisions and the reasons for them.
4.
Construction Problems or Revisions (As They Develop) Not all construction problems can be anticipated during the design of the structure; therefore, construction problems arise that require revisions. Calculations for revisions made during construction should be included in the design/check calculation file when construction is completed.
D. File Exclusions The following items should not be included in the file:
July 2000
1.
Geometric calculations.
2.
Irrelevant computer information.
3.
Prints of Office Standard Sheets.
4.
Irrelevant sketches.
5.
Voided sheets.
1.3-11
BRIDGE DESIGN MANUAL Criteria General Information
Design Procedures and Processes
6.
Preliminary design calculations and drawings unless used in the final design.
7.
Test hole logs.
8.
Quantity calculations.
E. Upon completion of the design work, fill out a Design Completed Checklist (Form 230-035). (See Appendix 1.3-A3.)
1.3.3
Office Copy Review Office Copy is the compiled contract documents (plans/specials) of all involved disciplines (Region, service center, and Bridge Office). It is normally distributed for final review for compatibility, completeness, and accuracy before final printing and going to Ad with the contract.
1.3.4
a.
Note the due date to determine priority.
b.
Review the comments from any previous reviews of the Region PS&E and check to see if the items have been corrected.
c.
Review all indexes for items related to traffic signals, illumination, signs, retaining walls, traffic barrier, and other structural items.
d.
Review the index and verify that no bridge plans have been omitted.
e.
Review pertinent sections of the special provisions for consistency with the plans, design criteria, and specifications.
f.
Verify that Standard Plans and preapproved plans are called out where applicable.
g.
Review pertinent plan sheets.
h.
Verify consistency between Region plans and bridge plans; particularly geometry, drainage, guardrail, and other pertinent items.
i.
Determine if any nonstandard designs are shown or specified. If so, a structural review of them may be necessary. Note any missing specifications, Standard Plans, etc.
j.
Return plans and comments to the unit manager.
Addenda Plan or specification revisions during the advertising period require an addendum. The Bridge Projects Engineer will evaluate the need for the addendum after consultation with the OSC Bridge Construction Engineer, Region, and the Plans Branch. The Bridge Design Engineer or the design unit manager must initial all addenda. For addenda to contract plans, obtain the original drawing from the Bridge Project Unit. Use shading to mark all changes (except deletions) and place a revision note at the bottom of the sheet (Region and Plans Branch jointly determine addendum date) and a description of the change. Return the original and an 11 × 17 reduced copy to the Bridge Project Unit who will submit the reduced copy to the Plans Branch for processing. See Chapter 10, Section 10.1.1I, for additional information. For changes to specifications, submit a copy of the page with the change to the Bridge S&E Unit for processing.
1.3-12
July 2000
BRIDGE DESIGN MANUAL Criteria General Information 1.3.5
Design Procedures and Processes
Shop Plans The following is intended to be a guide for checking shop plans. A. Bridge Shop Plans 1.
Mark one copy of each sheet with the following, near the title block, in red pencil or with a rubber stamp: Office Copy Contract (number) (Checker’s initials) (Date)
2.
On the Bridge Office copy, mark with red pencil any errors or corrections. Yellow shall be used for highlighting the checked items, and ordinary lead (gray) pencil for other comments, arithmetic, etc. (Only the red pencil marks will be copied onto the other copies to be returned to the contractor.)
3.
Items to be checked are typically as follows: Check against Contract Plans, Special Provisions, and Standard Specifications. a.
Material specifications (ASTM specifications, hardness, alloy and temper, etc.).
b.
Size of member and fasteners.
c.
Length dimensions if shown on the Contract Plans.
d.
Finish (surface finish, galvanizing, anodizing, painting, etc.).
e.
Weld size and type and welding procedure if required.
f.
Strand or rebar placement, jacking procedure, stress calculations, elongations, etc.
g.
Fabrication — reaming, drilling, and assembly procedures.
h.
Adequacy of details.
i.
Erection procedure.
The following items pertain only to post-tensioning shop plans: j.
Center of gravity of post-tensioning (P/T) strands matches contract plans.
k.
Seating loss.
l.
Friction losses.
m. Time-dependent losses.
July 2000
n.
Steel stress diagram.
o.
Elongation of strands in all tendons. These will be compared with the field measurements. (See WSDOT Construction Manual.) For curved bridges where the lengths of the exterior webs vary by more than 2 percent, separate elongations should be provided for each web.
p.
Anchor plate size. If nonstandard, check bearing stress on concrete and flexural stress in plate material. Test data must be on file to substantiate the adequacy of internal type anchorages.
1.3-13
BRIDGE DESIGN MANUAL Criteria General Information
Design Procedures and Processes
q.
Vent conduit at all high and low points in the spans.
r.
Adequate room in the concrete members for the system.
s.
Interference with other reinforcement. Special attention to this item if post-tensioning (P/T) supplier proposes a different number of tendons than shown on the plans.
t.
Offsets from soffit to bottom of conduits. Watch for sharp curvature of tendons near end anchorages (see minimum radius requirements in Chapter 6 of BDM Criteria).
u.
Strand positions in conduit in sag and summit tendon curves.
v.
Stressing sequence.
w. Geometric details such as size of blockouts. Note: Manufacturer’s details may vary slightly from contract plan requirements but must be structurally adequate and reasonable. 4.
5.
Items Not Requiring Check: a.
Quantities in bill of materials.
b.
Length dimensions not shown on Contract Plans except for spot checking.
Project Engineer’s Copy If one copy has been marked by the Project Engineer (in green), do not use this as the office copy. Transfer his corrections, if pertinent, to the office copy using red pencil.
6.
Marking Copies When finished, mark the office copy with one of three categories (in red pencil, lower right corner). a.
APP’D (Approved, No Corrections required.)
b.
AAN (Approved as noted — minor corrections only. Do not place written questions on an approved as noted sheet.)
c.
RFC (Return for correction — major corrections are required followed by resubmittal.)
If in doubt between AAN and RFC, check with the unit manager. An acceptable detail may be shown in red. Mark the plans Approved-As-Noted provided that the detail is clearly noted Suggested Correction — Otherwise Revise and Resubmit. Do not mark the other copies. This will be done in the Construction Support Unit. The reviewer may be asked to proof the other copies after they have been marked. Notify Project Engineer of any approved changes to the contract plans. Also notify the OSC Bridge Construction Engineer, who may have to approve a change order and provide justification for the change order.
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BRIDGE DESIGN MANUAL Criteria General Information
Design Procedures and Processes
If problems are encountered which may cause a delay in the checking of the shop plans or completion of the contract, notify the unit manager and the Construction Support Unit. Return all shop drawings and Contract Plans to the Construction Support unit when checking is completed. Include a list of any deviations from the Contract Plans which are allowed and a list of any disagreements with the Project Engineer’s comments (regardless of how minor they may be). If deviations from the Contract Plans are to be allowed, a Change Order may be required. Alert the Construction Support Unit so that their transmittal letter may inform the Region and the OSC Bridge Construction Engineer. B. Sign Structure, Signal, and Illumination Shop Plans In addition to those instructions described under “Bridge Shop Plans,” the following instructions apply:
1.3.6
1.
Review the shop plans to ensure that the pole sizes conform to the Contract Plans. Determine if fabricator has supplied plans for each pole or type of pole called for in the contract.
2.
The Project Engineer’s copy may show shaft lengths where not shown on Contract Plans or whether a change from Contract Plans is required. Manufacturer’s details may vary slightly from contract plan requirements, but must be structurally adequate to be acceptable.
Contract Plan Changes (Change Orders and As-Builts) A. Request for Changes The following is intended as a guide for processing changes to the design plans after a project has been awarded. For projects which have been assigned a Bridge Technical Advisor, structural design change orders can be approved at the Regional level provided the instructions outlined in the Construction Manual are followed. For all other projects, all changes are to be channeled through the Construction Support Unit which will coordinate with the OSC Bridge Construction Engineer. Responses to inquiries should be handled as follows: 1.
Request by Contractor or Supplier A designer, BTA, or design unit manager contacted directly by a contractor/supplier may discuss a proposed change with the contractor/supplier, but shall clearly tell the contractor/supplier to formally submit the proposed change though the Project Engineer and that the discussion in no way implies approval of the proposed change. Designers are to inform their manager if they are contacted.
2.
Request From the Project Engineer Requests for changes directly from the Project Engineer to the design unit manager should be discouraged but may be acceptable when the Bridge Construction Engineer is not available. The Bridge Construction Engineer and Construction Support Unit should be informed of any changes.
3.
Request From the Region Construction Engineer Requests from the Region Construction Engineer are to be handled like requests from the Region Project Engineer.
July 2000
1.3-15
BRIDGE DESIGN MANUAL Criteria General Information 4.
Design Procedures and Processes
Request From the OSC Bridge Construction Engineer Requests for changes from the OSC Bridge Construction Engineer or his/her assistants are usually made through the Construction Support Unit and not directly to the Design Unit. However, sometimes, it is necessary to work directly with the Design Unit. The Construction Support Unit should be informed of any decisions made involving changes to the Contract Plans.
5.
Request From the Design Unit Request for changes from the Design Unit due to plan error, omissions, etc., shall be discussed with the Bridge Design Engineer prior to revising and issuing new plan sheets.
B. Processing Contract Revisions Changes to the Contract Plans or Specifications subsequent to the award of the contract may require a contract revision. To clearly identify the scope of work, it is often desirable to provide revised or additional drawings. When a revision or an additional drawing is necessary, request the original mylars from the Construction Support Unit’s Plans Technician and prepare revised or new original mylars. Send the new mylars to the Construction Support Unit’s Plans Technician. The OSC Construction Office requires two reduced paper copies; Construction Support Unit requires one reduced paper copy; Design Unit requires one or more reduced paper copies; one full-sized paper print, stamped “As Constructed Plans,” shall be sent to the Project Engineer who shall use it to mark construction changes and upon project completion, forward them to the Construction Support Bridge Plans Technician. The Designer is responsible for making the prints and distributing them. This process applies to all contracts including OSC Ad and Award, Region Ad and Award, or Local Agency Ad and Award. Whenever new plan sheets are required as part of a contract revision, the information in the title blocks of these sheets must be identical to the title blocks of the contract they are for (e.g., Job Number, Contract No., Fed. Aid Proj. No., Approved by, and the Project Name). These title blocks shall also be initialed by the Bridge Design Engineer, manager, designer, and reviewer of the change before they are distributed. If the changes are modifications made to an existing sheet, the sheet number will remain the same. A new sheet shall be assigned the same number as the one in the originals that it most closely applies to and shall also be given a letter (e.g., the new sheet applies to the original sheet 25 of 53 so it will be number 25A of 53). A full size mylar of the contract revision sheet shall be stored in the Bridge Projects Unit. Every revision will be assigned a number which shall be enclosed inside a triangle (e.g., 1 ). The assigned number shall be located both at the location of the change on the sheet and in the revision block of the plan sheet along with an explanation of the change. Any revised sheets shall be sent to the OSC Construction Office with a written explanation describing the changes to the contract, justification for the changes, and a list of material quantity additions or subtractions.
1.3-16
July 2000
BRIDGE DESIGN MANUAL Criteria General Information 1.3.7
Design Procedures and Processes
Archiving Design Calculations, Design Files, and S&E Files Upon Award, the following information will be collected by the Bridge Standard Plans Engineer. • Design File • S&E File • Design Calculations Place a job file cover sticker on the file folder (see Figure 1). Fill in all fields completely. Keep these files on site for future reference until the end of the retention period. Update the file with any contract plan changes that occur during construction. After the retention period, send the files to the Office of the Secretary of State for archiving at: Archives & Records Management 1129 Washington Street SE Olympia, WA 98504-0238 Telephone: 360-586-4900
SR # _____ County ____________________ CS # _____ Bridge Name _____________________________________ Bridge # _______________ Contract # ________________ Contents ________________________________________ Designed by _____________ Checked by _____________ Archive Box # _____________________ Vol. # _______
Figure 1
P65:DP/BDM1
July 2000
1.3-17
BRIDGE DESIGN MANUAL Criteria General Information 1.4
Coordination With Other Divisions and Agencies
Coordination With Other Divisions and Agencies During the various phases of design, it is necessary to coordinate the elements of the bridge design function with the requirements of other divisions and agencies. E-mail messages, telephone calls, and other direct communication with other offices are necessary and appropriate. Adequate communications are essential but organizational format and lines of responsibility must be recognized. However, a written request sent through channels is required before work can be done or design changes made on projects.
1.4.1
Preliminary Planning Phase See Chapter 2.1 of this manual for coordination required at preliminary planning phase.
1.4.2
Final Design Phase A. Coordination With Region During this phase, final coordination of the bridge design with region requirements must be accomplished. This is normally done with the Region Project Engineer, Region Design Engineer, or Region Plans Engineer. Details such as division of quantity items between the region PS&E and bridge PS&E become highly important to a finished contract plan set. The region PS&E and bridge PS&E are combined by the Region Plans Branch. However, necessary coordination should be accomplished before this time. During the design of a project for a region level contract, the region shall provide a copy of the proposed structural plans (such as retaining walls, barrier, large culverts, etc.) to the Bridge and Structures Office. Bridge and Structures Office will review these plans and indicate any required changes, then send them back to the region. The region shall incorporate the changes prior to contract advertisement. After contract advertisement, the region shall return the original plan sheets to Bridge and Structures Office. These sheets shall be held in temporary storage until the “As Constructed Plans” for them are completed by the region. The region shall then transmit the “As Constructed Plans” to Bridge and Structures Office where they will be transferred to the original plans for permanent storage. Upon request, the region will be provided copies of these plans by Bridge and Structures Office. B. Technical Design Matters Technical coordination must be done with the OSC Materials Laboratory Foundation Engineer and with the OSC Hydraulic Engineer for matters pertaining to their responsibilities. A portion of the criteria for a project design may be derived from this coordination, otherwise it shall be developed by the designer subject to approval of the Bridge Design Engineer. When two or more structures are to be let under the same contract, the designer should make a special effort to be uniform on structural details, bid items, specifications, and other items.
P:DP/BDM1 9807-0802
August 1998
1.4-1
BRIDGE DESIGN MANUAL Criteria General Information 1.5
Bridge Design Scheduling
1.5.1
General
Bridge Design Scheduling
The Bridge Projects Engineer is responsible for scheduling and monitoring the progress of projects. The “Bridge Design Schedule” is used to track the progress of a project and is updated monthly. A typical project would involve the following steps: A. Regions advise Bridge and Structures Office of an upcoming project. B. The Bridge Projects Unit estimates design time required for preliminary plans, design, and S&E (see Section 1.5.2). C. The project is entered into the Bridge Design Schedule with start and due dates for site data preliminary plan, project design, PS&E, and the ad date. D. Bridge site data received. E. Preliminary design started. F. Final Design Started — Designer estimates time required for final plans (see Section 1.5.3). G. Monthly Schedule Update — Each Design Unit Supervisor turns in to the Bridge Scheduling Engineer an updated copy of the Bridge Design Schedule showing man-months used last month, man-months used to date, percentage complete, and adjustments required in the schedule. The report is due by the fourth working day of the month. H. Project turned in to S&E unit.
1.5.2
Preliminary Design Schedule The preliminary design estimate done by the Bridge Projects Unit is based on historical records from past projects factoring in unique features of each individual project, the efficiencies of designing similar bridges on the same project, CADD system efficiencies, designer experience, and other factors as appropriate.
1.5.3
Final Design Schedule A. Breakdown of Project Man-Hours Required Using a spreadsheet, list each item of work required to complete the project and the man-hours required to accomplish them. Certain items of work may have been partially completed during the preliminary design, and this partial completion should be reflected in the columns “% Completed” and “Date Completed.” Formerly, WSDOT Form 232-002 (see Appendix 1.5-A1), was used to monitor project progress. This form can still be used. The designer or team leader should research several sources when making the final design time estimate. The following are possible sources that may be used: The “Bridge Design Summary” contains records of design time and costs for past projects. The summary is kept in the Bridge Projects Unit. The times given include preliminary plan, design, check, drafting, and supervision as reported on the summary from the Accounting Office. The Bridge Projects Unit has “Bridge Construction Cost Summary” books. These are grouped according to bridge types and have records of design time, number of drawings, and bridge cost. The hours shown are the total for the bridge as reported from the designer’s time sheets.
August 1998
1.5-1
BRIDGE DESIGN MANUAL Criteria General Information
Bridge Design Scheduling
B. Estimate Design Time Required The designer or design team leader shall determine an estimate of design time required to complete the project. The use of a spreadsheet, Microsoft Project, or other means is encouraged to ensure timely completion and adherence to the schedule. In the past, WSDOT Form 232-003 was used. Typically, the following completion percentages (percent of the total project time) from Form 232-002 are applied on Form 232-003 for the following activities: Activity No.
Percentage
1 2 3 4 5 7
40 20 25 5 5 5
Completion percentages for Activities 4, 5, and 7 are approximately 5 percent of the project total. Activity 6 is separate from design time required by needs to be included to determine the completion date. Activities 8 and 9 are estimates dependant on individual circumstances. Note: Activities 1 through 5 and Activity 7 make up 100 percent of the design time required to complete the job. The individual activities include the specific items as follows under each major activity. Activity No. 1
Activity No. 2
1.5-2
Design — Includes: 1.
Project coordination.
2.
Geometric computations.
3.
Design calculations (including time for Load Rating).
4.
Complete check of all plan sheets by the designer.
5.
Supervisor time related to design (estimate 10 percent of design time).
Design Check — As defined in Section 1.3.1A3 — Includes: 1.
Checking design at maximum stress locations.
2.
Checking major items on the drawings, including geometrics.
3.
Additional checking required.
4.
Supervisor time related to checking (estimate 10 percent of design check time).
August 1998
BRIDGE DESIGN MANUAL Criteria General Information Activity No. 3
Bridge Design Scheduling Drawings — Includes: Preparation of all drawings.
Activity No. 4
Activity No. 5
Activity No. 6
Activity No. 7
Revisions — Includes: 1.
Revisions resulting from the checker’s check.
2.
Revisions resulting from the supervisory review.
Quantities — Includes: 1.
Compute quantities including bar list.
2.
Check quantities.
S&E — Includes: 1.
Preparing special provisions checklist.
2.
Assemble backup data covering any unusual feature.
Review — Includes: 1.
Activity No. 8
Other Jobs — Includes: 1.
Activity No. 9
Supervisor’s review.
Interruptions.
Leave — Includes: 1.
Annual, sick, and other leave.
See Figures 1.5.2-1 and 2 for sample Bar Chart problem and corresponding progress report form. C. Monthly Project Progress Report The designer or design team leader is responsible for determining monthly project progress and reporting the results to the Unit Supervisor. In the past, WSDOT Form 232-004 (see Appendix 1.5-A2) was used to monitor the progress of the project design. The Design Unit Supervisor is required to update a copy of the bridge design schedule each month using information from the designer or design team leader. Any discrepancies between actual progress and the project schedule must be determined. Adjustments, either by revising the workforce assigned to the project, hours assigned to activities or, the project schedule, should be made accordingly. “Man-hours Used to Date” indicates the total number of hours used for each activity during the current period added to the total shown on the last report done. “% of Total Time Used” is the number of hours used for the activity divided by the current number of hours assigned to the activity from the “Current Estimate of Time to Complete” on Form 232-003. “% of Activity Complete” and “% of Total Project Complete” are estimates. Some activities will probably be ahead of schedule, some behind, and others on schedule. It is here that major discrepancies should be noticed and adjustments made as described above.
August 1998
1.5-3
BRIDGE DESIGN MANUAL Criteria General Information
Bridge Design Scheduling
The designer may use a computer spreadsheet, to track the progress of the project and as an aid in evaluating the percent complete. Other tools include using an Excel spreadsheet listing bridge sheet plans by title, bridge sheet number, percent design complete, percent design check, percent plan details completed, and percent plan details checked. A spreadsheet with this data allows the designer or design team leader to rapidly determine percent of project completion and where resources need to be allocated to complete the project on schedule.
P:DP/BDM1 9807-0802
1.5-4
August 1998
BRIDGE DESIGN MANUAL Criteria General Information
Bridge Design Scheduling Design Estimate Bar Chart Sample Criteria
The designer estimates that 792 man-hours will be required to complete the design phase of the project. The hours are distributed among Activities 1 through 7 and entered in the first column of the Bar Chart Form. Enter the percentage amount in column three. Estimate the time for Activity 8 (approximately 5 percent of subtotal) and for Activity 9 (approximately 8 percent of subtotal). Time from Activities 8 and 9 will not enter into job manpower estimates, but will affect the estimated completion date. Using a convenient scale, draw the bar chart. To compute the “Anticipated Completion Date,” scale from the “zero-line” to the farthest block on the right and to this add Activities 8 and 9 (in effect extending the completion time). Multiply this number by the scale you are using and divide by 8, and this will give you the number of working days to completion date. The number of working days in conjunction with the Working Day Calendar (see Bridge Projects Unit) will give the completion date. For this example, this will be: (5.5 + 1.2) × 100 × 1/8 = 84 working days August 2, 1982 — Start Date Number of working days
= =
6,475 +84 6,559
(from working day calendar) Dec. 2, 1982 (anticipated completion date)
Washington State Department of Transportation SR No.
Job No.
Design
2
Design Check
3
Drawings
4
Revisions
5
Quantities
6
S&E
7
Reviews Subtotals
8
Other Jobs
9
Leave Totals
Drawn By
Design Start Date
Scheduled Completion Date
Anticipated Completion Date
Completion Percentage
Layout By (Man Hours)
Current Estimate of Time to Complete
Original Estimate to Complete
(Man Hours)
Design Checked By
Activity
Activity No.
Designed By
1
Design Time Bar Chart
Project
Layout Check
Bar Chart
Layout Man Hours Scale: 1" = __________ Man Hours
100% 12345678 12345678 12345678 12345678 12345678 12345678 12345678 12345678 12345678 12345678 12345678 12345678 12345678 12345678 12345678 Remarks
DOT 232-003 (formerly C1M4) Rev 3/91
Figure 1.5.2-1
August 1998
1.5-5
BRIDGE DESIGN MANUAL Criteria General Information
Bridge Design Scheduling
Sample Progress Report Form Figure 1.5.2-2
1.5-6
August 1998
BRIDGE DESIGN MANUAL Criteria General Information 1.6
Bridge Design Scheduling
Guidelines for Bridge Site Visits The following guidelines are established to help all staff in determining the need for visiting bridge sites prior to final design. These guidelines should apply to consultants as well as to our own staff. In all cases, the associated region should be made aware of the site visit so that they would have the opportunity to participate. Region participation would be especially useful if a preliminary bridge plan is involved.
1.6.1
Bridge Rehabilitation Projects (excluding rail and minor expansion joint rehabilitation projects) For this type of bridge project, it is critical that the design team know as much as possible about the bridge that is to be rehabilitated. There is good information regarding the condition of existing bridges at the Bridge Preservation Office (Mottman). As-built drawings and contract documents are also helpful, but may not necessarily be accurate. At least one bridge site visit is necessary for this type of project. In some cases, an in-depth inspection with experienced condition survey inspectors would be appropriate. The decision to perform an in-depth inspection should include the Unit Supervisor, Region, and the Bridge Design Engineer.
1.6.2
Bridge Widenings and Seismic Retrofits For this type of bridge project, it is important that the design team is familiar with the features and condition of the existing bridge. There is good information regarding the condition of existing bridges at the Bridge Preservation Office (Mottman). As-built drawings and contract documents are also helpful, but may not necessarily be accurate. A site visit is recommended for this type of project, particularly if the bridge to be widened has unique features or is other than a standard prestressed girder bridge with elastomeric bearings.
1.6.3
Rail and Minor Expansion Joint Retrofits Generally, pictures and site information from the region along with as-builts and condition survey information are adequate for most of these types of projects. However, if there is any doubt about the adequacy of the available information or concern about accelerated deterioration of the structure elements to be retrofitted, a site visit is recommended.
1.6.4
New Bridges Generally, pictures and site information from the region are adequate for most new bridge designs. However, if the new bridge is a replacement for an existing bridge, a site visit is recommended, particularly if the project requires staged removal of the existing bridge and/or staged construction of the new bridge.
1.6.5
Bridge Demolition If a bridge demolition is required as part of a project, a site visit would help the design team determine if there are unique sit restrictions that could affect the demolition. If unique site restrictions are observed, they should be properly documented, included in the job file and noted on the special provisions checklist. Before making a site visit, the Condition Survey Unit and the region should be contacted to determine if there are any unique site conditions or safety hazards. Proper safety equipment and procedures should always be incorporated into any site visit. When making a site visit, it is important to obtain as much information as possible. Pictures, video records with spoken commentary, field measurements, and field notes are appropriate forms of field information. A written or pictorial record should be made of any
August 1998
1.6-1
BRIDGE DESIGN MANUAL Criteria General Information
Bridge Design Scheduling
observed problems with an existing bridge or obvious site problem. The site visit data would then be incorporated into the job file. This information will be a valuable asset in preparing constructable and cost-effective structural designs. When negotiating with consultants for structural design work, it is important to make appropriate site visits part of the consultants’s scope of work.
P:DP/BDM1 9807-0802
1.6-2
August 1998
BRIDGE DESIGN MANUAL Criteria General Information 1.99
Bibliography
Bibliography 1.
Standard Specifications for Highway Bridges, Latest Edition and Interims, American Association of State Highway and Transportation Officials (AASHTO).
2.
LRFD Bridge Design Specifications, Latest Edition and Interims. American Association of State Highway and Transportation Officials (AASHTO).
3.
Organization Handbook, Washington State Department of Transportation.
4.
WSDOT Design Manual.
5.
WSDOT Construction Manual.
P:DP/BDM1 9807-0802
August 1998
1.99-1
BRIDGE DESIGN MANUAL Appendix A General Information
Standard Design Criteria Form
STANDARD DESIGN CRITERIA PROJECT
SR
MADE BY
CHECKED BY
DATE
SUPV.
STANDARD DESIGN CRITERIA FOR THIS STRUCTURE
ITEM
1
STANDARD SPECIFICATIONS FOR HIGHWAY BRIDGES AASHTO_________TH EDITION, 19___________
2
INTERIM SPECIFICATION, 19____________(IF USED)
3
STATE OF WASHINGTON, STANDARD SPECIFICATIONS FOR ROAD, BRIDGE, AND MUNICIPAL CONSTRUCTION, 19__________
4
STATE OF WASHINGTON, STANDARD PLANS FOR ROAD, BRIDGE, AND MUNICIPAL CONSTRUCTION WITH REVISIONS TO 19____________
5
BRIDGE DESIGN MANUAL, VOLUME_____________, WITH REVISIONS TO 19___________
6
OTHER_______________________________________________________________________________________________________
7
DESIGN BY: LOAD FACTOR____________________________________________________________________________________ WORKING STRESS________________________________________________________________________________
8
9
STEEL REINFORCING BARS: A.A.S.H.T.O.
M31
GRADE 60_______________
A.A.S.H.T.O.
M31
GRADE 40______________
CONCRETE: F'C = 4000 PSI (CLASS AX) F'C = 3000 PSI (CLASS B) F'C = _________ PSI (LIGHTWEIGHT)
3
DENSITY = ________________ LBS. PER FT.
OTHER__________________________________________________________________________________________________ 10
PRESTRESSED GIRDERS: SERIES, __________________________________
SPECIAL,_________________________________
STANDARD CONCRETE DENSITY = ___________________________ LBS.
FT.3
/
LIGHTWEIGHT CONCRETE DENSITY = _______________________________LBS.
/
FT.3
MINIMUM CONCRETE STRENGTH AT STRAND RELEASE = _______________________________PSI MINIMUM CONCRETE STRENGTH AT 28 DAYS = ________________________________________PSI FOUNDATION DATA FROM SOILS
11 PIER NO.
PILE/SPREAD
ALLOWABLE SOIL p
MAXIMUM DESIGN SOIL p OR PILE LOAD DESIGNER
GROUP
CHECKER
GROUP
1 2 3 4 5 6
August 1998
1.3-A1-1
BRIDGE DESIGN MANUAL Appendix A General Information
Standard Design Criteria Form
ITEM
12
STANDARD DESIGN CRITERIA FOR THIS STRUCTURE
STEEL STRUCTURES: INDICATE BY SPECIFICATION THE DIFFERENT TYPES OF STEEL USE A.A.S.H.T.O.
M-
A.A.S.H.T.O.
M-
A.A.S.H.T.O.
M-
A.A.S.H.T.O.
M-
ROLLERS
A.A.S.H.T.O.
M-
CASTINGS
OTHER 13
SPECIAL CRITERIA: SEE FORM ENTITLED “EXCEPTIONS TO THE STANDARD DESIGN CRITERIA“
230-030
DOT Revised 1/89
1.3-A1-2
August 1998
BRIDGE DESIGN MANUAL Appendix A General Information
Exceptions to the Standard Design Criteria Form
Project
SR No.
Made By
Check By
Supervisor
Date
EXCEPTIONS TO THE STANDARD DESIGN CRITERIA No.
Gen. Area
Addition or Modification
App’d By
DOT 230-032 (formerly C1M3) Rev 3/91
August 1998
1.3-A2
BRIDGE DESIGN MANUAL Appendix A General Information
August 1998
Design Completed Checklist
1.3-A3
BRIDGE DESIGN MANUAL Appendix A General Information
Job File Table of Contents
Job File Table of Contents Item
August 1998
Date
Who
Subject
1.3-A4
BRIDGE DESIGN MANUAL Appendix A General Information
Office Time Report
Bridge and Structures Office Time Report _______________ Region PRELIMINARY PLAN:
L-Number ___________
Design Unit Staffing Level estimate __________
Start Date: ____________________ Completion Date: _______________ TIME CHARGED Design ____________ Check ____________ Drafting ___________ Review ___________ Total _____________
DESIGN AND DETAIL
Hours Hours Hours Hours Hours
Standard _______________
Design Unit Staffing Level estimate __________
Start Date: ____________________ Completion Date: _______________ TIME CHARGED Design ____________ Check ____________ Drafting ___________ Review ___________ Total _____________
August 1998
Hours Hours Hours Hours Hours
Standard _______________
1.3-A5
BRIDGE DESIGN MANUAL Appendix A General Information
Not Included in Bridge Quantities List
Not Included In Bridge Quantities List Environmental And Engineering Service Center Bridge and Structures Office
SR
Job Number
Designed By
Checked By
Project Title Date
Supervisor
Type of Structure
The following is a list of items for which the Bridge and Structures Office is relying on the Region to furnish plans, specifications and estimates. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. DOT
Form 230-038 EF Revised 2/97
August 1998
1.3-A6
BRIDGE DESIGN MANUAL Appendix A General Information
August 1998
Special Provisions Checklist
1.3-A7-1
BRIDGE DESIGN MANUAL Appendix A General Information
1.3-A7-2
Special Provisions Checklist
August 1998
BRIDGE DESIGN MANUAL Appendix A General Information
August 1998
Special Provisions Checklist
1.3-A7-3
BRIDGE DESIGN MANUAL Appendix A General Information
1.3-A7-4
Special Provisions Checklist
August 1998
BRIDGE DESIGN MANUAL Appendix A General Information
August 1998
Special Provisions Checklist
1.3-A7-5
BRIDGE DESIGN MANUAL Appendix A General Information
1.3-A7-6
Special Provisions Checklist
August 1998
DOT 232-002 (formerly C1M5) Rev 3/91
19 20 21 22
16 17 18
Drawing or Item
% Completed
Hours Required
% Completed
Draw
Check Drawing
Made By
Comments
Date
General Information
3 4 5 6 7 8 9 10 11 12 13 14 15
1 2
No.
Hours Required
Check % Completed
Design Hours Required
Project
By
SR
% Completed
Job No.
Date Completed
By
Date Completed
By
Breakdown of Project Manhours Required
Hours Required
August 1998 Date Completed
Washington State Department of Transportation
Appendix A BRIDGE DESIGN MANUAL
Breakdown of Project Manhours Required Form
1.5-A1
Date Completed
By
DOT 232-004 (formerly C1M4) Rev 3/91
Totals
9
8
7
6
5
4
3
2
1
Man Hours Used to Date
As of
Man Hours Used to Date
As of As of
Man Hours Used to Date
% of Total Time Used
% of Total Time Used
Reference No.
% of Total Time Used
Reference No. Reference No.
As of
Man Hours Used to Date
% of Activity Complete
Project
% of Total Time Used
Reference No.
987654321 9 8765432 987654321 9876543211 987654321 76543210987654321 7 654321098765432 76543210987654321 76543210987654321 76543210987654321 76543210987654321 76543210987654321 76543210987654321 76543210987654321 76543210987654321 765432109876543211 76543210987654321
Job No.
987654321 98765432 987654321 9876543211 987654321 6543210987654321 6 543210987654321 654321098765432 6543210987654321 6543210987654321 6543210987654321 6543210987654321 6543210987654321 6543210987654321 6543210987654321 65432109876543211 6543210987654321
SR
99887766554433221 987654321 9876543211 987654321 66543210987654321 54321098765432 6543210987654321 6543210987654321 6543210987654321 6543210987654321 6543210987654321 65432109876543211 65 4321098765432 6543210987654321 65432109876543211 6543210987654321
% of Total Project Complete
% of Activity Complete
% of Total Project Complete
% of Activity Complete
Monthly Project Progress Report
Monthly Project Progress Report Form General Information
1.5-A2 % of Total Project Complete
August 1998
987654321 98765432 987654321 9876543211 987654321 6543210987654321 654321098765432 6543210987654321 6543210987654321 6543210987654321 65432109876543211 6543210987654321 6543210987654321 6543210987654321 654321098765432 65432109876543211 6543210987654321
Washington State Department of Transportation
Appendix A
BRIDGE DESIGN MANUAL
% of Total Project Complete
% of Activity Complete
Activity No.
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Contents Page
2.0 2.1 2.1.1 2.1.2 2.1.3 2.1.4 2.1.5
2.2 2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
Preliminary Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preliminary Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Interdisciplinary Design Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Value Engineering Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preliminary Project Recommendations (Existing Bridges) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preliminary Project Recommendations (New Bridges) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Type, Size, and Location Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. TS&L General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. TS&L Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Reviews and Submittal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preliminary Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Development of the Preliminary Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Site Reconnaissance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Coordination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Consideration of Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Designer Recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Concept Approval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Inspection and Maintenance Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Job File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Bridge Site Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Request for Preliminary Foundation Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Request for Preliminary Hydraulics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Design Report or Design Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Other Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Factors for Consideration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Site Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Economic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Structural . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Environmental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Aesthetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Hydraulic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Permits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Coast Guard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Approvals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Bridge Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Bridge Architect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Railroad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
August 1998
2.1-1 1 1 1 1 2 2 2 3 4 2.2-1 1 1 1 1 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 5 5 5 5 5 6
2.0-i
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Contents Page
2.3 2.3.1
2.3.2
2.3.3
2.3.4
2.3.5
2.3.6 2.3.7 2.3.8 2.3.9 2.3.10
2.4 2.4.1
2.0-ii
Preliminary Plan Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Highway Crossings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Bridge Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Horizontal Clearances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Vertical Clearances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. End Slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Determination of Bridge Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Pedestrian Crossings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Bridge Redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Railroad Crossings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Bridge Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Horizontal Clearances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Crash Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Vertical Clearances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Determination of Bridge Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Special Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Water Crossings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Bridge Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Horizontal Clearances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Vertical Clearances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. End Slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Determination of Bridge Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Scour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Pier Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Construction Access and Time Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bridge Widenings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Bridge Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Traffic Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Construction Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Detour Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Bridge Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Live Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Retaining Walls and Noise Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bridge Deck Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bridge Deck Protective Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction Clearances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inspection and Maintenance Acces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Safety Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Travelers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Selection of Structure Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bridge Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Reinforced Concrete Flat Slab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Reinforced Concrete Tee Beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3-1 1 1 1 1 2 2 2 4 4 4 4 4 4 5 5 5 5 5 6 6 6 6 6 6 7 7 7 8 8 8 8 8 8 8 9 9 9 9 10 10 11 11 2.4-1 1 1 1
August 1998
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Contents Page
2.4.2 2.5 2.5.1 2.5.2
2.5.3 2.5.4
2.5.5 2.6 2.6.1 2.6.2 2.6.3 2.7 2.7.1
2.99
C. Reinforced Concrete Box Girder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Post Tensioned Concrete Box Girder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Prestressed Concrete Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Composite Steel Plate Girder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Composite Steel Box Girder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Steel Truss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. Segmental Concrete Box Girder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Railroad Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . K. Timber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L. Other . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wall Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aesthetic Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Visual Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . End Piers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Wing Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Retaining Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Slope Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intermediate Piers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Barrier and Wall Surface Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Plain Surface Finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Fractured Fin Finish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Pigmented Sealer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Superstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structure Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Handling and Shipping of Precast Members and Steel Beams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Salvage of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . WSDOT Standard Highway Bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Substructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Superstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 2 3 3 3 4 4 5 5 5 5 2.5-1 1 1 1 1 1 1 2 2 2 2 2 2.6-1 1 1 1 2.7-1 1 1 1 1 2 2.99-1
Appendix A — Design Aids 2.2-A1 Bridge Site Data General 2.2-A2 Bridge Site Data Rehabilitation 2.2-A3 Bridge Site Data Stream Crossings 2.2-A4 Preliminary Plan Checklist 2.3-A1 Bridge Stage Construction Comparison 2.3-A2 Bridge Redundancy Criteria 2.4-A1 Bridge Selection Guide 2.7-A1 Standard Superstructure Elements 2.7-A2 Standard Pier Elements
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BRIDGE DESIGN MANUAL Criteria Preliminary Design
Contents
Appendix B — Design Examples 2.2-B1 Preliminary Plan Bridge Replacement 2.2-B2 Preliminary Plan Bridge Widening 2.2-B3 Preliminary Plan New Bridge
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Preliminary Design
2.1
Preliminary Studies
2.1.1
Interdisciplinary Design Studies
Preliminary Studies
As part of the preparation for a major project, an Interdisciplinary Design Team (IDT) may be established by the region. The IDT is composed of members of different expertise and backgrounds, selected from regions, the Service Center, and outside agencies. The IDT members and the support groups serve to give an objective analysis and review of the various design alternatives for the region’s project. They contribute ideas and participate in the selection of design alternatives. This work will often culminate in the publication of the Environmental Impact Statement (EIS). Bridge Design Engineers are often asked to be a part of this process, either as a support resource or as a member of the IDT itself.
2.1.2
Value Engineering Studies Value Engineering (VE) is a process of review and analysis of a project. The VE team seeks to define the most cost-effective means of satisfying the basic function(s) of the project. Usually a VE study takes place before or during the time that the region is working on the design. Occasionally a VE study examines a project with a completed PS&E. A VE team is typically made up of members of different expertise and backgrounds, selected from the region, Service Center, and outside agencies. The Team Facilitator will lead the team through the VE process. The team will review the project as defined by the project’s design personnel. They will seek to decide the basic function(s) that are served by the project, brainstorm to develop other alternatives to serve the same function(s), and evaluate these alternatives on how well they satisfy these basic functions. The VE team will present their findings in a presentation to the region. The region is then required to investigate these findings further and address them in the design. Bridge Design Engineers are often asked to be a part of this process, either as support contacts or as VE team members. The process usually involves three to five days.
2.1.3
Preliminary Project Recommendations (Existing Bridges) Projects that call for the rehabilitation of an existing bridge require that the existing condition of the bridge be reviewed and a recommendation the existing bridge be prepared. When a region starts a design for such a project, they will request by an Inter-Departmental (IDC) memorandum that the Bridge and Structures Office make Preliminary Project recommendations. This will provide them with a scope of work and a cost estimate for the project. It involves review of the inspection and condition reports from the Bridge Preservation Section and a site visit with the region and other project stakeholders. Special inspections of certain portions of the structure may need to be scheduled to determine the load capacity of the existing bridge, what types of rehabilitation work need to be done, the extended life span achieved by certain types of rehabilitation work, and to develop various alternatives with cost estimates for comparison, ranging from “do nothing” to “replacement.” A typical recommendation consists of two parts. The first is a report to the file providing detailed information related to the bridge rehabilitation and a summary of the various alternatives considered and an itemized list of the rehabilitation work with the associated costs. The second part is an IDC to the region discussing the overall project in general terms mentioning any particular items of concern to the region and a summary of the preferred alternatives with recommendations. The region should be given the opportunity to review a draft report and IDC and provide input prior to finalization.
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BRIDGE DESIGN MANUAL Criteria Preliminary Design 2.1.4
Preliminary Studies
Preliminary Project Recommendations (New Bridges) Projects that call for a new bridge require that a recommendation for the new structure be prepared. While a region is preparing a design for a project, they will seek assistance from the Bridge and Structures Office by writing an IDC. This request could range from confirmation of construction cost data to consideration of various structure designs or staging alternatives. An IDC to the region will provide recommendations and information. A face to face meeting with the region project staff is recommended.
2.1.5
Type, Size, and Location Studies It is the policy of the Federal Highway Administration (FHWA) that major or unusual bridges must go through the preparation of a Type, Size, and Location (TS&L) study. The TS&L study will outline the project, describe the proposed structure and other design alternatives considered, and show justification for the selection of the preferred alternative. Approval of the TS&L study by FHWA is the basis for advancing the project to the design stage. The FHWA requires a TS&L study for tunnels, movable bridges, unusual structures, and major structures with deck areas greater than 125,000 square feet. This is a guideline only. Smaller bridges that are unusual may also require a TS&L study while some, such as long viaducts, may not. As early as possible in the Project Development stage, the FHWA should be contacted for conformation. The preparation of the TS&L study is the responsibility of the Bridge and Structures Office. The TS&L cannot be submitted to FHWA until after the Environmental documents have been submitted. However, TS&L preparation need not wait for Environmental document approval, but may begin as soon as the bridge site data is available. See Chapter 1110 of the Design Manual for the type of information required for a bridge site data submittal. A. TS&L General In order to become familiar with the project, the designer should first review its history. The Environmental and Design Reports should be reviewed. The bridge site data should be scrutinized so that additional data, maps, or drawings can be requested. After reviewing the history of the project, a meeting with region and a site visit should be arranged. In order to have foundation information, the Materials Lab must be contacted early. FHWA expects specific recommendations on the foundation type. The Materials Lab will submit a detailed foundation report for inclusion as an appendix to the TS&L study. In order to find the preferred structural alternative, the designer should:
2.1-2
l.
Develop a list of all the feasible alternatives. At this stage of the process, the range of alternatives should be kept wide open. Brainstorming with supervisors and other engineers can help bring out fresh and innovative solutions.
2.
Eliminate the unusable alternatives by applying the constraints of the project. Question restrictive constraints and document their bases. At the end of this step, there should be no more than four alternatives.
3.
Perform preliminary level design calculations for unique structural problems to ensure that the remaining alternatives are feasible.
4.
Compare the advantages, disadvantages, and costs of the remaining alternatives to determine the preferred alternative(s).
5.
Visit the project site with the region and Geotech Branch.
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BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Studies
After piers have been located, a memorandum request for a Hydraulics Report should be made to the Olympia Service Center Hydraulics Unit. FHWA expects specific information on scour and backwater on both falsework and permanent piers. The Olympia Service Center Hydraulics Unit will submit a report for inclusion as an appendix to the TS&L study. The Bridge Architect at the Bridge and Structures Office should be consulted early on and throughout the study process “Notes to the file” should be made documenting the aesthetic requirements and recommendations of the Architect. Cost backup data is needed for any costs used in the TS&L study. FHWA expects TS&L costs based on estimated quantities. This data is to be included in an appendix to the TS&L study. It is a good idea to coordinate the quantities submitted are in a form compatible with the estimator’s cost breakdown method. B. TS&L Outline The TS&L study should describe the project, the proposed structure, and give reasons why the bridge type, size, and location were selected. 1.
Cover, Title Sheet, and Contents These should identify the project and the contents of the TS&L.
2.
Photographs There should be enough color photographs to provide the look and feel of the area. The prints should be numbered and labeled and the location indicated on a diagram.
3.
Introduction The introduction describes the report and references other reports used to prepare the TS&L study. The following reports should be listed if used. • Design Reports and Supplements • Environmental Reports • Architectural or Visual Assessment Reports • Hydraulic Report • Geotechnical Reports
4.
Project Description The project description is intended to summarize the preferred alternative of the project design so that the TS&L study clearly defines the project. Care should be taken to describe the project adequately but briefly. A vicinity map should be shown.
5.
Design Criteria Design criteria states to what code, loading, etc., the bridge will be constructed. Besides the AASHTO specifications and assorted AASHTO guide specifications, other criteria are sometimes used. These criteria should be listed. Examples of this would be the temperature loading used for segmental bridges or areas defined as wetlands.
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BRIDGE DESIGN MANUAL Criteria Preliminary Design 6.
Preliminary Studies
Structural Studies The structural studies section documents how the proposed structure type, size, and location were determined. The following considerations should be addressed. • Aesthetics • Cost Estimates • Geometric constraints • Project staging • Foundations • Hydraulics • Feasibility of construction • Structural constraints • Maintenance This section should have a narrative style describing how these factors point to the preferred alternative. Show how each constraint eliminated or supported the alternatives. For instance, “Because the geometry required a 200-foot span, prestressed concrete girders could not be used” or “Restrictions on falsework placement forced the use of self supporting precast concrete or steel girders.”
7.
Executive Summary The executive summary should be able to stand alone as a separate document. The project and structure description should be given. Present the recommended alternative with its cost and include a summary of considerations used to choose or eliminate alternatives.
8.
Drawings Preliminary Plan drawings of the recommended alternative are included in the appendix. The drawings show the plan, elevation, and typical section. For projects where alternative designs are specified as recommended alternatives, Preliminary Plans for each of these structure types shall be included. Supplemental drawings showing special features, such as complex piers, are often provided to clearly define the project.
C. Reviews and Submittal While writing the TS&L study, all major decisions should be discussed with the unit supervisor, who can decide if the Bridge Design Engineer needs to be consulted. A peer review meeting with the Bridge Design Engineer should be scheduled at 50 percent completion. The FHWA Bridge Engineer should be invited to provide input. The final report must be reviewed, approved, and the Preliminary Plan drawings signed by the Bridge Architect, the Bridge Projects Engineer, the Bridge Design Engineer, and the Bridge and Structures Engineer. The TS&L study is submitted with a cover letter to FHWA signed by the Bridge and Structures Engineer.
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BRIDGE DESIGN MANUAL Criteria Preliminary Design 2.2
Preliminary Plan
Preliminary Plan The Preliminary Plan is the most important phase of bridge design as it sets the groundwork for the final design. The intent is to completely define the bridge geometry so final roadway design by the regions and the structural design by the Bridge and Structures Office can take place with minimal revisions. During the region’s preparation of the highway design, they also begin work on the bridge site data. Region submits the bridge site data to the Bridge and Structures Office which initiates the start of the Preliminary Plan. Information that must be included as part of the bridge site data submittal is outlined in Chapter 1110 of the Design Manual.
2.2.1
Development of the Preliminary Plan A
Responsibilities In general, the responsibilities of the designer, checker, detailer, and supervisor are as specified in Chapter 1 of the Bridge Design Manual. The primary design engineer is responsible for developing a Preliminary Plan for the structure that is compatible with geometric, aesthetic, staging, geotechnical, hydraulic, financial, and structural requirements and conditions that exist at the site. Upon receipt of the bridge site data from the region, the designer shall review it for completeness and verify that what the project calls for is realistic and structurally feasible. Any omissions or corrections are to be called to the region’s attention immediately. The supervisor shall be kept informed of progress on the preliminary plan so that the schedule can be monitored. Should problems develop, the supervisor can make adjustments to the schedule or manpower assignments. The designer must keep the job file up to date by documenting all conversations, meetings, requests, questions, and approvals concerning the project. Notes to the designer, and details not shown in the Preliminary Plan shall be documented in the job file. The checker shall give an independent review of the plan, verifying that it is in compliance with the site data as provided by the region and as corrected in the job file. The plan shall be compared against the Preliminary Plan checklist to ensure that all necessary information is shown. The checker is to review the plan for consistency with office design practice, detailing practice, and for constructibility. The preliminary plan shall be drawn using current office CAD equipment and software by the Engineer or Detailer.
B. Site Reconnaissance The site data submitted by the region will include a video and photographs of the site. Even for minor projects, this may not be enough information for the designer to work from in developing the Preliminary Plan. For most bridge projects, site visits are necessary. Site visits with region project staff and other project stakeholders such as Hydraulics, Design, and Geotech Branch should be arranged with the knowledge and approval of the Bridge Projects Engineer. C
Coordination The designer is responsible for coordinating the design and review process throughout the project. This includes seeking input from various WSDOT units and outside agencies.
D. Consideration of Alternatives In the process of developing the Preliminary Plan, the designer should brainstorm, develop, and evaluate various design alternatives. Depending on how the General Factors for Consideration (Section 2.2.3) apply to a particular site, the number of alternatives will usually be limited to only a
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BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan
few for most projects. For some smaller projects and most major projects, design alternatives merit development and close evaluation. The process of considering and rejecting design alternatives provides documentation for the preferred alternative. E. Designer Recommendation Once the designer has done a thorough job of evaluating the needs and limitations of the site, analyzed all information and developed and evaluated design alternatives for the project, he should be able to make a recommendation for the optimum solution. Based on this recommendation, the designer should discuss the recommendation with the Bridge Projects Engineer. F. Concept Approval For some projects, the presentation, in “E” above, to the Bridge Projects Engineer will satisfy the need for concept approval. Large complex projects, projects of unique design, or projects where two or more alternatives appear viable, should be presented to the Bridge Design Engineer for his concurrence before plan development is completed. For unique or complex projects a presentation is made to the Bridge and Structures Office Peer Review Committee. G. Inspection and Maintenance Access In the process developing the Preliminary Plan, the design engineer should consult with the Bridge Preservation Section for input.
2.2.2
Documentation A. Job File When a memorandum IDC, transmitting site data from the region is received by the Bridge and Structures Office, a job file is created. This official job file serves as a depository for all communications and resource information for the job. Scheduling and time estimates are logged in this file, as well as cost estimates, preliminary quantities, and documentation of all approvals. When the Preliminary Plan is completed, the job file continues to serve a useful purpose as a communications and documentation depository for all pertinent project-related information during the design process. B. Bridge Site Data All Preliminary Plans are developed from site data as submitted by the region. This submittal will consist of a memorandum IDC, and appropriate attachments as specified by Chapter 1110 of the Design Manual. When this information is received, it should be reviewed for completeness so that missing or incomplete information can be noted and requested. C. Request for Preliminary Foundation Data A Request for Preliminary Foundation Data is sent to Geotech Branch to solicit any foundation data that is available at this preliminary stage. The Geotech Branch is provided with approximate dimensions for overall structure length and width, an approximate number of intermediate piers (if applicable), and approximate stations for beginning and end of structure on the alignment. Based on test holes from previous construction in the area, geological maps, and soil surveys. The Materials Lab responds by IDC giving an analysis of what foundation conditions arc likely to be encountered and what types of substructure are best suited for these conditions.
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BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan
D. Request for Preliminary Hydraulics A Request for Preliminary Hydraulics data is sent to the Hydraulics Office to document hydraulic requirements that must be considered in the structure design. The Hydraulics Office is provided with the contour plan and other bridge site data. Seal vent elevations, normal water, 100-year flood and 500-year flood elevations, and flows (Q), pier configuration, scour depth and minimum footing cover, ice pressure, minimum waterway channel width, riprap requirements, and minimum clearance to the 100-year flood elevation are provided in an ºIDC response from the Hydraulics Office. E. Design Report or Design Summary Some bridge construction projects have a Design Report or Design Summary prepared by the region. This is a document which includes design considerations and conclusions reached in the development of the project. It defines the scope of work for the project. It serves to document the design standards and applicable deviations for the roadway alignment and geometry. It is also an excellent reference for project history, safety and traffic data, environmental concerns, and other information. F. Other Resources For some projects, preliminary studies or reports will have been prepared. These resources can provide additional background for the development of the Preliminary Plan. G. Notes if meetings with Regions and other project stakeholders shall be included in the documentation.
2.2.3
General Factors for Consideration Many factors must be considered in preliminary bridge design. Some of the more common of these are listed in general categories below. These factors will be discussed in appropriate detail in subsequent portions of this manual. A. Site Requirements Topography Alignment (tangent, curved, skewed) Vertical profile and superelevation Proposed or existing utilities B. Safety Feasibility of falsework (impaired clearance and sight distance) Density and speed of traffic Detours or possible elimination of detours by staging construction Sight distance Horizontal clearance to piers Hazards to pedestrians, bicyclists Inspection and Maintenance Access (UBIT clearances) (see Figure 2.3.10-1) C. Economic Funding classification (federal and state funds, state funds only, local developer funds) Funding level
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2.2-3
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan
D. Structural Limitation on structure depth Requirements for future widening Foundation and groundwater conditions Anticipated settlement E. Environmental Site conditions (wetlands, environmentally sensitive areas) EIS requirements Mitigating measures F. Aesthetic General appearance Compatibility with surroundings and adjacent structures Visual exposure and importance G. Construction Ease of construction Falsework clearances and requirements Erection problems Hauling difficulties and access to site Construction season Time limit for construction H. Hydraulic Bridge deck drainage Stream flow conditions and drift Passage of flood debris Scour, effect of pier as an obstruction (shape, width, skew, number of columns) Bank and pier protection Consideration of a culvert as an alternate solution Permit requirements for navigation and stream work limitations I.
Other Prior commitments made to other agency officials and individuals of the community Recommendations resulting from preliminary studies
2.2.4
Permits A. Coast Guard As outlined in Chapter 240 of the Design Manual, the Bridge and Structures Office is responsible for coordinating and applying for Coast Guard permits for bridges over waterways. This is handled by the Coast Guard Liaison Engineer in the Bridge Projects Unit of the Bridge and Structures Office. A determination of whether a bridge requires a permit is known before the bridge site data is received. Generally, tidal-influenced waterways and waterways used for commercial navigation will require Coast Guard permits. However, some waterways may qualify for an exemption from a permit if certain conditions apply including the exclusion of use by vessels larger than 21 feet long. The
2.2-4
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BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan
process of getting this exemption, from FHWA, not the Coast Guard, is the responsibility of the region. The Coast Guard Liaison Engineer should be asked to check with the region and the Coast Guard to confirm the situation on a case by case basis. For all waterway crossings, the Coast Guard Liaison Engineer is required to initial the Preliminary Plan as to whether a Coast Guard permit or exemption is required. This box regarding Coast Guard permit status is located in the center left margin of the plan. If a permit is required, the permit target date will also be noted. The reduced print, signed by the Coast Guard Liaison Engineer, shall be placed in the job file. The work on developing the permit application should be started such that it is ready to be sent to the Coast Guard eight months before the project ad date. The Coast Guard Liaison Engineer should be given a copy of the Preliminary Plan from which to develop the plan sheets that are part of the permit. B. Other All other permits will be the responsibility of the region. The Bridge and Structures Office may be asked to provide information to the region to assist them in making applications for these permits.
2.2.5
Approvals A. Bridge Design When the Preliminary Plan has been checked by the checker and signal by the Bridge Projects Engineer, it is ready to go to the Bridge Design Engineer and the Bridge and Structures Engineer for approval. B. Bridge Architect For all preliminary plans, the Architect should be aware and involved when the designer is first developing the plan. The Architect should be presented with a reduced print of the plan by the designer. This is done prior to the job going to the checker. The Architect will review the print and signify his approval by signing it. This print is placed in the job file. If future plan revisions change elements of aesthetic importance, the Architect should be asked to review and approve, by signature, a print of the revised plan. For large, multiple bridge projects, the Bridge Architect should be contacted for development of a coordinated architectural concept for the project corridor. The architectural concept for a project corridor is generally developed in draft form and reviewed with the project stakeholders prior to finalizing. C. Region Prior to the completion of the preliminary plan the designer should meet with the region to discuss the concept and get their input. When the Preliminary Plan and the “Not Included in Bridge Quantities List” along with the preliminary plan transmittal IDC. The region will review the plan for compliance and agreement with their original site data. They will work to answer any notes to the region that have been listed on the plan. When this review is complete, the Regional Administrator, or his representative, will sign the plan. The region will send back a print of the plan with any comments noted in red (additions) and green (deletions) along with responses to the notes to the region.
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BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan
D. Railroad When a railroad is involved with a structure on a Preliminary Plan, the Right of Way Accommodation Engineer of the Design Office must be involved during the plan preparation process. A copy of the Preliminary Plan is sent to the Right of Way Accommodation Engineer, who then sends a copy to the railroad involved for their comments and approval. The railroad will respond with approval by letter to the Right of Way Accommodation Engineer. A copy of this letter is then routed to the Bridge and Structures Office and is placed in the job file.
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BRIDGE DESIGN MANUAL Criteria Preliminary Design 2.3
Preliminary Plan Criteria
2.3.1
Highway Crossings
Preliminary Plan Criteria
A. General A highway crossing is defined as a grade separation between two intersecting roadways. A highway crossing is further categorized as either an undercrossing or an overcrossing. 1.
Undercrossing A bridge which provides for passage of a state highway under a less important state highway, a county road, or a city street is called an undercrossing. Relative importance between state highways is indicated by functional classification. For details, see Chapter 440 of the Design Manual. For example, a bridge included as a part of an interchange involving SR 182 (Interstate) and SR 14 (Principal) and providing for passage of traffic on SR 182 under SR 14 would be called SR 14 I/C Undercrossing.
2.
Overcrossing A bridge which carries traffic on a state highway over a less important state highway, a county road, or a city street is called an overcrossing. For example, a bridge which carries traffic on SR 5 over Hamilton Road would be called Hamilton Road Overcrossing.
B. Bridge Width The bridge roadway channelization is provided by the region with the Bridge Site Data. For state highways, the roadway geometrics are controlled by Chapters 430 and 440 of the Design Manual. For city and county arterials, the roadway geometrics are controlled by Chapter IV of the Local Agency Guidelines. C. Horizontal Clearances Safety dictates that fixed objects be placed as far from the edge of the roadway as is economically feasible. Criteria for minimum horizontal clearances to bridge piers and retaining walls are outlined in the Design Manual. Chapter 710 of the Design Manual outlines clear zone and recovery area requirements for horizontal clearances without guardrail or barrier being required. Actual horizontal clearances shall be shown in the plan view of the Preliminary Plan (to the nearest 0.1 foot). Minimum horizontal clearances to inclined columns or wall surfaces should be provided at the roadway surface and for a vertical distance of 6 feet above the edge of pavement. When bridge end slopes fall within the recovery area, the minimum horizontal clearance should be provided for a vertical distance of 6 feet above the fill surface. See Figure 2.3.1-1. Bridge piers and abutments ideally should be placed such that the minimum clearances can be satisfied. However, if for structural or economic reasons, the best span arrangement requires a pier to be within clear zone or recovery area, then guardrail or barrier can be used to mitigate the hazard. There are instances where it may not be possible to provide the minimum horizontal clearance even with guardrail or barrier. An example would be placement of a bridge pier in a narrow median. The required column size may be such that it would infringe on the shoulder of the roadway. In such cases, the New Jersey barrier shape would be incorporated into the shape of the column. Barrier or
August 1998
2.3-1
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan Criteria
guardrail would need to taper into the pier at a flare rate satisfying the criteria in Chapter 710 of the Design Manual. See Figure 2.3.1-2. The reduced clearance to the pier would need to be approved by the region. D. Vertical Clearances The required minimum vertical clearances are established by the functional classification of the highway and the construction classification of the project. For state highways, this is as outlined in Chapters 430 and 440 of the Design Manual. For city and county arterials, this is as outlined in Chapter IV of the Local Agency Guidelines. Actual minimum vertical clearances are shown on the Preliminary Plan (to the nearest 0.1 foot). The approximate location of the minimum vertical clearance is noted in the upper left margin of the plan. For structures crossing divided highways, minimum vertical clearances for both directions are noted. E. End Slopes The type and rate of end slope used at bridge sites is dependent on several factors. Soil conditions and stability, right of way availability, fill height or depth of cut, roadway alignment and functional classification, and existing site conditions are all important. The region should have made a preliminary determination based on these factors during the preparation of the bridge site data. The side slopes noted on the Roadway Section for the roadway should indicate the type and rate of end slope. The Materials Lab will recommend the minimum rate of end slope. This should be compared to the rate recommended in the Roadway Section and to existing site conditions (if applicable). The types of end slopes and the conditions for which each are applicable are spelled out in Chapter 640 of the Design Manual. End slope protection may be required at certain highway crossings, as spelled out in Chapter 1120 of the Design Manual. Examples of slope protection are shown on Standard Plan D-9. F. Determination of Bridge Length Establishing the location of the end piers for a highway crossing is a function of the profile grade of the overcrossing roadway, the minimum vertical and horizontal clearances required for the structure, and the type and rate of end slope used. For the general case of bridges in cut or fill slopes, the control point is where the cut or fill slope plane meets the bottom of ditch or edge of shoulder as applicable. From this point, the fill or cut slope plane is established at the recommended rate up to where the slope plane intersects the grade of the roadway at the shoulder. Following the requirements of Standard Plan H-9, the back of pavement seat, end of wing wall or end of retaining wall can be established at 3 feet behind the slope intersection. For the general case of bridges on wall type or “closed” abutments, the controlling factors are the required horizontal clearance and the size of the abutment. This situation would most likely occur in an urban setting or where right of way is limited.
2.3-2
August 1998
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan Criteria
Horizontal Clearance to Inclined Piers 1990 Figure 2.3.1-1
Bridge Pier in Narrow Median 1990 Figure 2.3.1-2
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2.3-3
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan Criteria
G. Pedestrian Crossings Pedestrian crossings follow the same format as highway crossings. Geometric criteria for pedestrian facilities are established in Chapter 1020 of the Design Manual. Width and clearances would be as established there and as confirmed by region. Unique items to be addressed with pedestrian facilities include ADA requirements, the railing to be used, handrail requirements, overhead enclosure requirements, and profile grade requirements for ramps and stairs. H. Bridge Redundancy Design bridges to minimize the risk of catastrophic collapse by using redundant supporting elements (columns and girders). For substructure design use: One column minimum for roadways 28 feet wide and under. Two columns minimum for roadways over 28 feet to 40 feet. Three columns minimum for roadways over 40 feet to 60 feet. Collision protection or design for collision loads for piers with one or two columns. For superstructure design use: Three girders (webs) minimum for roadways 32 feet and under. Four girders (webs) minimum for roadways over 32 feet. See Appendix 2.3-A2 for details. Note: Any deviation from the above guidelines shall have a written approval by the Bridge Design Engineer.
2.3.2
Railroad Crossings A. General A railroad crossing is defined as a grade separation between an intersecting highway and a railroad. A bridge which provides highway traffic over the railroad is called an overcrossing. A bridge which provides highway traffic under the railroad is called an undercrossing. Requirements for railroad separations for both undercrossings and overcrossings may involve negotiations with the railroad company concerning clearances, geometrics, utilities, and maintenance roads. The railroad’s review and approval, will be based on the completed Preliminary Plan. B. Criteria The initial Preliminary Plan shall be prepared in accordance with the criteria of this section to apply uniformly to all railroads. Variance from this criteria will be negotiated with the railroad, when necessary, after a Preliminary Plan has been provided for their review. C. Bridge Width For railroad overcrossings, the provisions of Section 2.3.1 pertaining to bridge width of highway crossings shall apply. Details for railroad undercrossings will depend on the specific project and the railroad involved.
2.3-4
August 1998
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan Criteria
D. Horizontal Clearances For railroad undercrossings, the provisions of Section 2.3.1 pertaining to horizontal clearances for highway crossings shall apply. However, because of the heavy live loading of railroad spans, it is advantageous to reduce the span lengths as much as possible. For railroad undercrossings skewed to the roadway, piers may be placed up to the outside edge of 8-foot (minimum) shoulders if certain conditions are met (structural requirements, satisfactory aesthetics, satisfactory sight distance, etc.). The actual minimum horizontal clearances are shown in the Plan view of the Preliminary Plan (to the nearest 0.1 foot). For railroad overcrossings, minimum horizontal clearances are as noted below: Railroad Alone Fill Section
14 feet
Cut Section
16 feet
Horizontal clearance shall be measured from the center of the outside track to the face of pier. When the track is on a curve, the minimum horizontal clearance shall be increased at the rate of 11/2 inches for each degree of curvature. An additional 8 feet of clearance for off-track equipment shall only be provided when specifically requested by the railroad. E. Crash Walls Crash walls, when required, shall be designed to conform to the criteria from of the AREA Manual. F. Vertical Clearances For railroad undercrossings, the provisions of Section 2.3.1 pertaining to vertical clearances of highway crossings shall apply. For railroad overcrossings, the minimum vertical clearance shall satisfy the requirements of Chapter 1120 of the Design Manual. The actual minimum vertical clearances are shown on the Preliminary Plan (to the nearest 0.1 foot). The approximate location of the minimum vertical clearance is noted in the upper left margin of the plan. G. Determination of Bridge Length For railroad overcrossings, the provisions of Section 2.3.1 pertaining to the determination of bridge length shall apply. For railroad overcrossings, the minimum bridge length shall satisfy the minimum horizontal clearance requirements. The minimum bridge length shall generally satisfy the requirements of Figure 2.3.2-1. H. Special Considerations For railroad overcrossings, the top of footings for bridge piers or retaining walls adjacent to railroad tracks shall be 2 feet or more below the top of tie. The footing face shall not be closer than 10 feet to the center of the track. Any cofferdams, footings, excavation, etc., encroaching within 10 feet of the center of the track requires the approval of the railroad.
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2.3-5
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan Criteria
For railroads, the minimum horizontal construction opening is 8 feet 6 inches to either side of the centerline of track. The minimum vertical construction opening is 22 feet 6 inches above the top of rail at 6 feet offset from the centerline of track. Falsework openings shall be checked to verify that enough space is available for falsework beams to span the required horizontal distances and still provide the minimum vertical falsework clearance. Minimum vertical openings of less than 22 feet 6 inches may be negotiated with the railroad through the Utilities-Railroad Engineer.
2.3.3
Water Crossings A. Bridge Width The provisions of Section 2.3.1 pertaining to bridge width for highway crossings apply here. B. Horizontal Clearances Water crossings over navigable waters requiring clearance for navigation channels shall satisfy the horizontal clearances required by the Coast Guard. Communication with the Coast Guard will be handled through the Coast Guard Liaison Engineer. For bridges over navigable waters, the centerline of the navigation channel and the horizontal clearances (to the nearest 0.1 foot) to the piers or the pier protection are shown on the Plan view of the Preliminary Plan. C. Vertical Clearances Vertical clearances for water crossings must satisfy floodway clearance and, where applicable, navigation clearance. Bridges over navigable waters must satisfy the vertical clearances required by the Coast Guard. Communication with the Coast Guard will be handled through the Coast Guard Liaison Engineer. The actual minimum vertical clearance (to the nearest 0.1 foot) for the channel span is shown on the Preliminary Plan. The approximate location of the minimum vertical clearance is noted in the upper left margin of the plan. The clearance shall be shown to the water surface as required by the Coast Guard criteria. Floodway vertical clearance will need to be discussed with the Hydraulics Office. In accordance with the flood history, nature of the site, character of drift, and other factors, they will determine a minimum vertical clearance for the 100-year flood. The roadway profile and the bridge superstructure depth must accommodate this. The actual minimum vertical clearance to the 100-year flood is shown (to the nearest 0.1 foot) on the Preliminary Plan, and the approximate location of the minimum vertical clearance is noted in the upper left margin of the plan. D. End Slopes The type and rate of end slopes for water crossings is similar to that for highway crossings. Soil conditions and stability, fill height, location of toe of fill, existing channel conditions, flood and scour potential, and environmental concerns are all important. As with highway crossings, the region, and Materials Lab will make preliminary recommendations as to the type and rate of end slope. The Hydraulics Office will also review the Regions’s recommendation for slope protection. E. Determination of Bridge Length Determining the overall length of a water crossing is not as simple and straight forward as for a highway crossing. Floodway requirements and environmental factors have a significant impact on where piers and fill can be placed.
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August 1998
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan Criteria
Determination of Bridge Length for a Railroad Undercrossing Figure 2.3.2-1
If a water crossing is required to satisfy floodway and environmental concerns, it will be known by the time the Preliminary Plan has been started. Environmental studies and the Design Report prepared by the region will document any restrictions on fill placement, pier arrangement, and overall floodway clearance. The Hydraulics Office will need to review the size, shape, and alignment of all bridge piers in the floodway and the subsequent effect they will have on the base flood elevation. The overall bridge length may need to be increased depending on the span arrangement selected and the change in the flood backwater, or justification will need to be documented. F. Scour The Hydraulics Office will indicate the anticipated depth of scour at the bridge piers. They will recommend pier shapes to best streamline flow and reduce the scour forces. They will also recommend measures to protect the piers from scour activity or accumulation of drift (minimum cover to top of footing, riprap, pier alignment to stream flow, closure walls between pier columns, etc.). G. Pier Protection For bridges over navigable channels, piers adjacent to the channel may require pier protection. The Coast Guard will determine whether pier protection is required. This determination is based on the horizontal clearance provided for the navigation channel and the type of navigation traffic using the channel. H. Construction Access and Time Restrictions Water crossings will typically have some sort of construction restrictions associated with them. These must be considered during preliminary plan preparation.
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2.3-7
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan Criteria
The time period that the contractor will be allowed to do work within the waterway may be restricted by regulations administered by various agencies. Depending on the time limitations, a bridge with fewer piers or faster pier construction may be more advantageous even if more expensive. Contractor access to the water may also be restricted. Shore areas supporting certain plant species are sometimes classified as wetlands. In order to work in or gain access through such areas, a work trestle may be necessary. Work trestles may also be necessary for bridge removal as well as new bridge construction.
2.3.4
Bridge Widenings A. Bridge Width The provisions of Section 2.3.1 pertaining to bridge width for highway crossings shall apply. In most cases, the width to be provided by the widening will be what is called for by the design standards, unless a deviation is approved. B. Traffic Restrictions Bridge widenings inherently involve traffic restrictions on the lanes above and where applicable on the lanes below. The bridge site data submitted by the district should contain information regarding temporary lane widths and staging configurations. This information should be checked to be certain that the existing bridge width, and the bridge roadway width during the intermediate construction stages of the bridge are sufficient for the lane widths, shy distances, temporary barriers, and construction room for the contractor. These temporary lane widths and shy distances are noted on the Preliminary Plan. The temporary lane widths and shy distances on the roadway beneath the bridge being widened should also be checked that adequate clearance is available for any substructure construction. C. Construction Sequence Using the traffic restriction data in the bridge site data, a construction sequence shall be developed. Such a sequence shall take into account necessary steps for construction of the bridge widening (substructure and superstructure), any construction work off of and adjacent to the structure, and the requirements of traffic flow on and below the structure. Checks shall be made to be certain that girder spacings, closure pours, and removal work are all compatible with the traffic arrangements. Projects with several bridges being widened at the same time should have sequencing that is compatible with the region’s traffic plans during construction and that allow the contractor room to work. It is important to meet with the region project staff to assure that the construction staging and characterization of traffic during construction is constructible and minimizes the impact to the traveling public.
2.3.5
Detour Structures A. Bridge Width The lane widths, shy distances, and overall roadway widths for detour structures are determined by the Region. Review and approval of detour roadway widths is done by the Traffic Office. B. Live Load Unless otherwise justified, all detour structures shall be designed for an AASHTO HS 15 live load. Construction requirements and staging can be sufficient reason to justify designing for a higher live load.
2.3-8
August 1998
BRIDGE DESIGN MANUAL Criteria Preliminary Design 2.3.6
Preliminary Plan Criteria
Retaining Walls and Noise Walls The requirements for Preliminary Plans for retaining walls and noise walls are similar to the requirements for bridges. The plan and elevation views define the overall limits and the geometry of the wall. The section view will show general structural elements that are part of the wall and the surface finish of the wall face. The most common types of walls are outlined in Section 9.4.2 of the Bridge Design Manual and Chapter 1130 of the Design Manual. The Bridge and Structures Office is responsible for Preliminary Plans for all nonstandard walls (retaining walls and noise walls) as spelled out in Chapter 1130 of the Design Manual.
2.3.7
Bridge Deck Drainage The Hydraulics Office provides a review of the Preliminary Plan with respect to the requirements for bridge deck drainage. As soon as the Preliminary Plan has been developed to the point that the length and width of the structure, profile grade, and superelevation diagram are shown on the plan, a reduced print shall be provided to the Hydraulics Office for their review. Any other pertinent information (such as locations of drainage off the structure) should be given to them also. For work with existing structures, the locations of any and all bridge drains shall be noted. The Hydraulics Office will determine the type of drains necessary (if any) and their location and spacing requirements. They will furnish any details or modifications required for special drains or special situations. If low points of sag vertical curves or superelevation crossovers occur within the limits of the bridge, the region should be asked to revise their geometrics to place these features outside the limits of the bridge. If such revisions cannot be made, the Hydraulics Office will provide details to handle drainage with bridge drains on the structure.
2.3.8
Bridge Deck Protective Systems The Preliminary Plan shall note in the lower left margin the type of deck protective system to be utilized on the bridge. The most commonly used systems are described in Section 8.4.7 of the Bridge Design Manual. New construction will generally be System 1 (21/2-inch concrete cover plus epoxy-coated rebars). System 2 (MC overlay) and System 3 (ACP overlay) are to be used on new construction that require overlays and on widenings for major structures. The type of overlay to be used should be noted in the bridge site data submitted by the region. The bridge condition report will indicate the preference of the Bridge and Structures Office and the Deck Systems Specialist in the Bridge and Structures Office.
2.3.9
Construction Clearances Most projects will involve construction in and around traffic. Both traffic and construction have to be accommodated. Construction clearances and working room must be reviewed at the Preliminary Plan stage to verify the constructibility of the project. For construction clearances for roadways, the region shall supply the necessary traffic staging information with the bridge site data. This includes temporary lane widths and shy distances, allowable or necessary alignment shifts, and any special minimum vertical clearances. With this information, the designer can establish the falsework opening or construction opening.
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2.3-9
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan Criteria
The horizontal dimension of the falsework or construction opening shall be the sum of the temporary traffic lane widths and shy distances, plus two 2-foot temporary concrete barriers, plus 2 feet shy behind these barriers. For multispan openings, a minimum of 2 feet shall be assumed for the interior support. This interior support shall also have 2 feet shy on both sides to the two 2-foot temporary concrete barriers that will flank it. The vertical clearance shall normally be 14 feet 6 inches minimum. The space available for the falsework must be enough for whatever depth is necessary to span the required horizontal opening. If the necessary depth is greater than the space available, either the minimum vertical clearance for the falsework shall be reduced or the horizontal clearance and span for the falsework shall be reduced. Preferably, the falsework span shall not exceed 38 feet. This limits the stresses in the new structure from the construction and concrete pouring sequences. While the falsework or construction openings are measured normal to the crossroad alignment, the falsework span is measured parallel to the bridge alignment. Once the construction clearances have been determined the designer should meet with the region to review the construction clearances to assure compatibility with the construction staging. This review should take place prior to finalization of the preliminary bridge plan. For railroads see Section 2.3.2H.
2.3.10 Inspection and Maintenance Access A. General Bridge inspection is required by the FHWA a minimum of every two years. The inspectors are required to access the bridge components to within 3 feet (1 meter). Maintenance forces need to access damaged members and locations that may collect debris. This is accomplished by using many methods. Safety cables, ladders, bucket trucks, Under Bridge Inspection Truck (UBIT), (see Figure 2.3.10-1), and under bridge travelers are just a few of the most common methods. Preliminary designers need to be aware of these requirements to assist the inspectors efforts over the life of the bridge. Access should be considered throughout the Preliminary Plan TS&L stages.
2.3-10
August 1998
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Preliminary Plan Criteria
Figure 2.3.10-1 B. Safety Cables Safety cables strung on steel plate girders or trusses allow for walking access. Care must be given to the application and location. Built-up plate girder bridges are detailed with a safety cable for inspectors walking the bottom flange. However, when the girders become more than 8 feet deep, the inspection of the top flange and top lateral connections becomes difficult. When the girders are less than 5 feet deep, it is not feasible for the inspectors to stand on the bottom flanges. On large trusses, large gusset plates (3 feet or more wide) are difficult to negotiate around. Cable are best run on the exterior of the bridge except at large gusset plates. At these locations, cables or lanyard anchors should be placed on the inside face of the truss. This way inspectors can utilize bottom lateral gusset plates to stand on while traversing around the main truss gusset. C. Travelers Under bridge travelers, placed on rails that remain permanently on the bridge, can be considered on large steel structures. This is an expensive option but it should be evaluated for large bridges with high ADT as access to the bridge would be limited by traffic windows that specify when a lane can be closed. Some bridges are restricted to weekend UBIT inspection for this reason. 4:P:BDM2
August 1998
2.3-11
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Selection of Structure Types
2.4
Selection of Structure Type
2.4.1
Bridge Types The following superstructure depth to span ratios have been determined from past experience to be reasonable and economical and are in some cases less than the minimum depth recommended by AASHTO. In this situation, the Bridge Design Manual will govern. The length of span used to determine superstructure depth shall be the length between centerline of bearings. Do not use the length between points of dead load contraflexure as noted in AASHTO for design. A. Reinforced Concrete Slab l.
Use Used for simple and continuous spans up to 60 feet.
2.
Characteristics Design details and falsework relatively simple. Shortest construction time for any cast-in-place structure. Correction for anticipated falsework settlement must be included in the dead load camber curve because of the single concrete pour.
3.
Depth/Span Ratios a.
Constant depth Simple spans Continuous spans
b.
1/22 1/25
Variable depth Adjust ratios to account for change in relative stiffness of positive and negative moment sections.
B. Reinforced Concrete Tee-Beam 1.
Use Used for continuous spans 30 feet to 60 feet. Has been used for longer spans with inclined leg piers.
2.
Characteristics Forming and falsework is more complicated than flat slab. Construction time is longer than for a flat slab.
3.
Depth/Span Ratios a.
Constant depth Simple spans Continuous spans
b.
1/13 1/15
Variable depth Adjust ratios to account for change in relative stiffness of positive and negative moment sections.
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2.4-1
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Selection of Structure Types
C. Reinforced Concrete Box Girder 1.
Use Used for continuous spans 50 feet to 130 feet. Maximum simple span 110 feet to limit excessive dead load deflections.
2.
Characteristics Forming and falsework is somewhat complicated. Construction time is approximately the same as for a tee-beam. High torsional resistance makes it desirable for curved alignments.
3.
Depth/Span Ratios* a.
Constant depth Simple spans Continuous spans
b.
1/18 1/20
Variable depth Adjust ratios to account for change in relative stiffness of positive and negative moment sections. *If the configuration of the exterior web is sloped and curved, a larger depth/span ratio may be necessary.
D. Post-Tensioned Concrete Box Girder 1.
Use Normally used for continuous spans longer than 130 feet or simple spans longer than 110 feet. Should be considered for shorter spans if a shallower structure depth is needed.
2.
Characteristics Construction time is somewhat longer due to post-tensioning operations. High torsional resistance makes it desirable for curved alignments.
3.
Depth/Span Ratios* a.
Constant depth Simple spans Continuous spans
b.
1/20.5 1/25
Variable depth Two span structures @ Center of span @ Intermediate pier
1/25 1/12.5
Multispan structures @ Center of span @ Intermediate pier
1/36 1/18
*If the configuration of the exterior web is sloped and curved, a larger depth/span ratio may be necessary.
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August 1998
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Selection of Structure Types
E. Prestressed Concrete Sections 1.
Use Local precast fabricators have several standard forms available for precast concrete sections based on WSDOT standard girder series plans. They are versatile enough to cover a wide variety of span lengths. WSDOT standard girders are:
2.
a.
W74G, W58G, W50G, and W42G prestressed, concrete I-girders requiring a cast-in-place concrete roadway deck.
b.
W53DG, and W35DG prestressed, concrete decked bulb tee girders requiring an ACP overlay roadway surface.
c.
12-inch, 18-inch, and 26-inch precast prestressed slabs requiring an ACP overlay roadway surface.
d.
26-inch precast prestressed tribeam requiring an ACP overlay roadway surface.
Characteristics Construction details and forming are fairly simple. Construction time is less than for a cast-in-place bridge. Little or no falsework is required.
F. Composite Steel Plate Girder 1.
Use For simple spans up to 260 feet and for continuous spans from 120 to 400 feet. Relatively low dead load when compared to a concrete superstructure makes this bridge type an asset in areas where foundation materials are poor.
2.
Characteristics Construction details and forming are fairly simple Construction time is comparatively short. Shipping and erecting of large sections must be reviewed. Cost of maintenance is higher than for concrete bridges. Current cost information should be considered because of changing steel market conditions.
3.
Depth/Span Ratios a.
Constant depth Simple spans Continuous spans
b.
1/22 1/25
Variable depth @ Center of span @ Intermediate pier
1/40 1/20
G. Composite Steel Box Girder 1.
Use For simple spans up to 260 feet and for continuous spans from 120 to 400 feet. Relatively low dead load when compared to a concrete superstructure makes this bridge type an asset in areas where foundation materials are poor.
August 1998
2.4-3
BRIDGE DESIGN MANUAL Criteria Preliminary Design 2.
Selection of Structure Types
Characteristics Construction details and forming are more difficult than for a steel plate girder. Shipping and erecting of large sections must be reviewed. Current cost information should be considered because of changing steel market conditions.
3.
Depth/Span Ratios a.
Constant depth Simple spans Continuous spans
b.
1/22 1/25
Variable depth @ Center of span @ Intermediate pier
1/40 1/20
Sloping webs are not used on box girders of variable depth. H. Steel Truss 1.
Use For simple spans up to 300 feet and for continuous spans up to 1,200 feet. Used where vertical clearance requirements dictate a shallow superstructure and long spans or where terrain dictates long spans and construction by cantilever method.
2.
Characteristics Construction details are numerous and can be complex. Cantilever construction method can facilitate construction over inaccessible areas. Through trusses are discouraged because of the resulting restricted horizontal and vertical clearances for the roadway.
3.
Depth/Span Ratios a. b.
Simple spans 1/6 Continuous spans @ Center of span @ Intermediate pier
I.
1/18 1/9
Segmental Concrete Box Girder 1.
Use For continuous spans from 200 to 700 feet. Used where site dictates long spans and construction by cantilever method.
2.
Characteristics Use of travelers for the form apparatus facilitates the cantilever construction method enabling long-span construction without falsework. Precast concrete segments may be used. Tight geometric control is required during construction to ensure proper alignment.
3.
Depth/Span Ratios Variable depth @ Center of span @ Intermediate pier
2.4-4
1/50 1/20
August 1998
BRIDGE DESIGN MANUAL Criteria Preliminary Design J.
Selection of Structure Types
Railroad Bridges 1.
Use For railroad undercrossings, most railroad companies prefer simple span steel construction. This is to simplify repair and reconstruction in the event of derailment or some other damage to the structure.
2.
Characteristics The heavier loads of the railroad live load require deeper and stiffer members than for highway bridges. Through girders can be used to reduce overall structure depth if the railroad concurs. Piers should be normal to the railroad to eliminate skew loading effects.
3.
Depth/Span Ratios Constant depth Simple spans Continuous two span Continuous multi-span
1/12 1/14 1/15
K. Timber 1.
Use Generally used for spans under 40 feet. Usually used for detour bridges and other temporary structures.
2.
Characteristics Excellent for short-term duration as for a detour. Simple design and details.
3.
Depth/Span Ratios Constant depth Simple span – Timber beam Simple span – Glulam beam Continuous spans
1/10 1/12 1/14
L. Other Bridge types such as cable-stayed, suspension, arch, tied arch, and floating bridges have special and limited applications. Their use is generally dictated by site conditions. Preliminary design studies will generally be done when these types of structures are considered.
2.4.2
Wall Types The process of selecting a type of retaining wall should economically satisfy structural, functional, and aesthetic requirements and other considerations relevant to a specific site. A detailed listing of the common wall types and their characteristics can be found in Section 9.4.2 of the Bridge Design Manual.
2:-4DTP:BDM2
August 1998
2.4-5
BRIDGE DESIGN MANUAL Criteria Preliminary Design 2.5
Aesthetic Considerations
2.5.1
General Visual Impact
Aesthetic Considerations
A bridge can be a strong feature in any landscape. Steps must be taken to assure that even the most basic structure will complement rather than detract from its surroundings. The Design Report, EIS, and bridge site data submitted by the region should each contain a discussion on the aesthetic importance of the project site. This commentary, along with the video and/or pictures submitted, will help the designer determine the appropriate structure. Generally a visit to the bridge site with the Bridge Architect and the region will be made as well. The Bridge Architect should be contacted early in the preliminary bridge plan process for input. Aesthetics is a very subjective element that must be factored into the design process in the otherwise very quantitative field of structural engineering. Bridges that are well proportioned structurally using the least material possible are generally well proportioned. However, the details such as pier walls, columns, and crossbeams require special attention to ensure a structure that will enhance the general vicinity.
2.5.2
End Piers A. Wing Walls The size and exposure of the wing wall at the end pier should balance, visually, with the depth and type of superstructure used. For example, a prestressed girder structure fits best visually with a 15-foot wing wall (or curtain wall/retaining wall). However, there are instances where a 20-foot wing wall (or curtain wall/retaining wall) may be used with a prestressed girder (maximizing a span in a remote area, for example). These guidelines shall be used with engineering judgment and with the review of the Bridge Architect. It is less expensive for bridges of greater than 40 feet of overall width to be designed with wing walls (or curtain wall/retaining wall) than to use a longer superstructure. B. Retaining Walls For structures at sites where profile, right of way, and alignment dictate the use of high exposed wall-type abutments for the end piers, retaining walls that flank the approach roadway can be used to retain the roadway fill and reduce the overall structure length. Stepped walls are often used to break up the height, and allow for landscape planting. A curtain wall runs between the bridge abutment and the heel of the abutment footing. In this way, the joint in the retaining wall stem can coincide with the joint between the abutment footing and the retaining wall footing. This simplifies design and provides a convenient breaking point between design responsibilities if the retaining walls happen to be the responsibility of the region. The length shown for the curtain wall dimension is an estimated dimension based on experience and preliminary foundation assumptions. It can be revised under design to satisfy the intent of having the wall joint coincide with the end of the abutment footing. C. Slope Protection The region is responsible for making initial recommendations regarding slope protection. It should be compatible with the site and should match what has been used at other bridges in the vicinity. The type selected shall be shown on the Preliminary Plan. It shall be noted on the “Not Included in Bridge Quantities” list.
August 1998
2.5-1
BRIDGE DESIGN MANUAL Criteria Preliminary Design 2.5.3
Aesthetic Considerations
Intermediate Piers The size, shape, and spacing of the intermediate pier elements must satisfy two criteria. They must be correctly sized and detailed to efficiently handle the structural loads required by the design and shaped to enhance the aesthetics of the structure. The primary view of the pier must be considered. For structures that cross over another roadway, the primary view will be a section normal to the roadway. This may not always be the same view as shown on the Preliminary Plan as with a skewed structure, for example. This primary view should be the focus of the aesthetic review. Tapers and flairs on columns should be kept simple and structurally functional. Fabrication and constructibility of the formwork of the pier must be kept in mind. Crossbeam ends should be carefully reviewed. Skewed bridges and bridges with steep profile grades or those in sharp vertical curves will require special attention to detail. Column spacing should not be so small as to create a cluttered look. Column spacing should be proportioned to maintain a reasonable crossbeam span balance.
2.5.4
Barrier and Wall Surface Treatments A. Plain Surface Finish This finish will normally be used on structures that do not have a high degree of visibility or where existing conditions warrant. A bridge in a remote area or a bridge among several existing bridges all having a plain finish would be examples. B. Fractured Fin Finish This finish is the most common and an easy way to add a decorative texture to a structure. Variations on this type of finish can be used for special cases. The specific areas to receive this finish should be reviewed with the Bridge Architect. C. Pigmented Sealer The use of a pigmented sealer can also be an aesthetic enhancement. The particular hue can be selected to blend with the surrounding terrain. Most commonly, this would be considered in urban areas. The selection should be reviewed with the Bridge Architect and the region.
2.5.5
Superstructure The horizontal elements of the bridge are perhaps the strongest features. The sizing of the structure depth based on the span/depth ratios in Section 2.4.1, will generally produce a balanced relationship. Haunches or rounding of girders at the piers can enhance the structure’s appearance. The use of such features should be kept within reason considering fabrication of materials and construction of formwork. The amount of haunch should be carefully reviewed for overall balance from the primary viewing perspective. The slab overhang dimension should approach that used for the structure depth. This dimension should be balanced between what looks good for aesthetics and what is possible with a reasonable slab thickness and reinforcement. For box girders, the exterior webs can be sloped. The amount of slope should not exceed l1/2: l for structural reasons. Sloped webs should only be used in locations of high aesthetic impact.
DP:BDM2
2.5-2
August 1998
BRIDGE DESIGN MANUAL Criteria Preliminary Design 2.6
Miscellaneous
2.6.1
Structure Costs
Miscellaneous
Historical bridge and structure cost data is outlined in Chapter 12. When using this data for cost estimates, the cost range assumed shall be based on the amount of information available. Unless foundation conditions are known, the worst case conditions would be assumed (e.g., pile foundations) for cost analysis. An estimate contingency of 10 percent (minimum) staff be added to all preliminary bridge plan estimates. For small projects or remote areas, high-range costs would be used. The cost data would be adjusted for inflation to the current date. Estimates include mobilization but not sales tax, engineering, future inflation, or contingencies, and the accuracy of the estimate is ±15 percent.
2.6.2
Handling and Shipping Precast Members and Steel Beams Bridges utilizing precast concrete beams or steel beams need to have their access routes checked and sites reviewed to be certain that the beams can be transported to the site. It must also be determined that they can be erected once they reach the site. Both the size and the weight of the beams must be checked. Likely routes to the site must be adequate to handle the truck and trailer hauling the beams. Avoid narrow roads with sharp turns, steep grades, and/or load-rated bridges which may prevent the beams from reaching the site. The Condition Survey Section of the Bridge and Structures Office should be consulted for limitations on hauling lengths and weights. The site should be reviewed for adequate space for the contractor to set up the cranes and equipment necessary to pick up and place the girders. The reach and boom angle should be checked and should accommodate standard cranes.
2.6.3
Salvage of Materials When a bridge is being replaced or widened, the material being removed should be reviewed for anything that WSDOT may want to salvage. Items such as aluminum rail, luminaire poles, sign structures, and steel beams should be identified for possible salvage. The region should be asked if such items are to be salvaged since they will be responsible for storage and inventory of these items.
DP:BDM2
August 1998
2.6-1
BRIDGE DESIGN MANUAL Criteria Preliminary Design 2.7
WSDOT Standard Highway Bridge
2.7.1
Design Elements
Miscellaneous
The following are standard design elements for highway undercrossings and overcrossings. They are meant to provide a generic base for consistent, clean looking bridges, and to reduce design and construction costs. Modification of some elements may be required, depending on site conditions. This should be determined on a case-by-case basis during the preliminary plan stage of the design process. A. General Fractured Fin Finish shall be used on the exterior face of the traffic barrier. All other surfaces shall be Plain Surface Finish. Exposed faces of wingwalls, columns, and abutments shall be vertical. The exterior face of the traffic barrier and the end of the intermediate pier crossbeam and diaphram shall have a 1:12 backslope. B. Substructure End piers use the following details: 15′-0″ wingwalls (Standard Cadd File WW15_21.FGB). Stub abutment wall with vertical face. Footing elevation, pile type (if required), and setback dimension are determined from recommendations in the WSDOT Materials Laboratory Foundation Report. Intermediate piers use the following details: “Semi-drop” Crossbeams: The crossbeam below the girders is designed for the girder and slab dead load, and construction loads. The crossbeam and the hinge diaphram together are designed for all live loads and composite dead loads. The crossbeam shall be 3′-0″ minimum depth. Round Columns: Columns shall be 3′-0″ or 4′-0″ in diameter. Dimensions are constant full height with no tapers. Bridges with roadway widths of 28′-0″ or less will generally be single column piers. Bridges with roadway widths of greater than 28′-0″ shall have two or more columns, following the criteria established in Section 2.3.1 H. C. Superstructure Concrete Slab: 7 1 2 ″ minimum thickness, with the top mat being epoxy coated steel reinforcing bars. Prestressed Girders: Girder spacing will vary depending on roadway width and span length. The slab overhang dimension is approximately half of the girder spacing. Girder spacings typically range between 6′-0″ and 8′-0″. W74G spans up to about 132″. (Standard Cadd File W74G.FGB). W58G spans up to about 110′. (Standard Cadd File W58G.FGB). Intermediate Diaphrams: Locate at the midspan for girders up to 80′ long. Locate at third points for girders over 80′ long. (Standard Cadd File DIA63A5.FGB). End Diaphrams: “End Wall on Girder” type. (Standard Cadd File DIA63A5.FGB). Traffic Barrier: New Jersey face barrier. (Standard Cadd File TB.FGB).
August 1998
2.7-1
BRIDGE DESIGN MANUAL Criteria Preliminary Design
Miscellaneous
Hinge Diaphram: Full width of crossbeam between girders and outside of the exterior girders. Exterior face is flush with the end of the crossbeam and matches the 1:12 slope of the crossbeam face. (Standard Cadd File TO BE DEVELOPED). BP Rail: 3′-6″ overall height for pedestrian traffic. 4′-6″ overall height for bicycle traffic. (Standard Cadd File BPRAIL.FGB). Sidewalk: 6″ height at curb line. Transverse slope of -.01′ per foot towards the curb line. (Standard Cadd File PED_BAR.FGB). Sidewalk barrier: Inside face is vertical. Outside face slopes 1:12 outward. (Standard Cadd File PED_BAR.FGB). D. Examples Appendices 2.7-A1 and A2 detail the standard design elements of a standard highway bridge. The following bridges are good examples of a standard highway bridge. However, they do have some modifications to the standard. SR 17 Undercrossing 395/110 Mullenix Road Overcrossing 16/203E&W
Contract 3785 Contract 4143
DTP:BDM2
2.7-2
August 1998
BRIDGE DESIGN MANUAL Criteria Preliminary Design 2.99
Bibliography
Bibliography 1.
Federal Highway Administration (FHWA) publication Federal Aid Highway Program Manual. FHWA Order 5520.1 (dated December 24, 1990) contains the criteria pertaining to Type, Size, and Location studies. Volume 6, Chapter 6, Section 2, Subsection 1, Attachment 1 (Transmittal 425) contains the criteria pertaining to railroad undercrossings and overcrossings.
2.
Washington Utilities and Transportation Commission Clearance Rules and Regulations Governing Common Carrier Railroads.
3.
American Railway Engineering Association (AREA) Manual for Railroad Engineering. Note: This is the criteria which we follow except as superseded by FHWA or WSDOT criteria. This manual is used as the basic design and geometric criteria by all railroads.
4.
Washington State Department of Transportation (WSDOT) Design Manual (M 22-01).
5.
Local Agency Guidelines (M 36-63).
6.
American Association of State Highway and Transportation Officials (AASHTO) Standard Specifications for Highway Bridges.
DTP:BDM2
August 1998
2.99-1
BRIDGE DESIGN MANUAL Appendix A Preliminary Design
Bridge Site Data General
Bridge Site Data General Region
Made By
Date
Bridge Information SR
Bridge Name
Control Section
Highway Section
Section, Township & Range
Project No.
Datum
What are expected foundation conditions?
Structure width between curbs ?
Will the structure be widened in a contract subsequent to this contract ?
Yes
No
N/A
Which side and amount ?
When can foundation drilling be accomplished?
Is slope protection or riprap required for the bridge end slopes?
Will the roadway under the structure be widened in the future? Stage construction requirements ?
Yes
No
N/A
Yes
No
N/A
Are sidewalks to be provided?
Yes
No
N/A
Yes
No
N/A
Yes
No
N/A
No
N/A
No
N/A
If Yes, which side and width?
Should the additional clearance for off-track railroad maintenance equipment be provided?
Will sidewalks carry bicycle traffic?
Can a pier be placed in the median?
Will signs or illumination be attached to the structure?
Yes
No
N/A
What are the required falsework or construction opening dimensions ?
Yes Will utility conduits be incorporated in the bridge?
Yes
Are there detour or shoofly bridge requirements? (If Yes, attach drawings) Yes
No
N/A
What do the bridge barriers transition to?
Can the R/W be adjusted to accommodate toe of approach fills?
Yes
No
N/A
What is the required vertical clearance?
Furnish type and location of existing features within the limits of this project, such as retaining walls, sign support structures, utilities, buildings, powerlines, etc.
What is the available depth for superstructure?
Are overlays planned for a contract subsequent to this contract ? Can profile be revised to provide greater or less clearance?
Yes
No
N/A
Yes
No
N/A
Any other data relative to selection of type, including your recommendations?
If Yes, which line and how much? Will bridge be contracted before, with or after approach fill?
Before
With
After
N/A
Attachments Vicinity Map Bridge Site Contour Map Specific Roadway sections at bridge site and approved roadway sections Vertical Profile Data Horizontal Curve Data Superelevation Transition Diagrams Tabulated field surveyed and measured stations, offsets, and elevations of existing roadways Photographs and video tape of structure site, adjacent existing structures and surrounding terrain
DOT Form 235-002 EF Revised 6/97
August 1998
2.2-A1
BRIDGE DESIGN MANUAL Appendix A Preliminary Design
Bridge Site Data Rehabilitation
Bridge Site Data Rehabilitation Region
Made By
Date
Bridge Information SR
Bridge Name
Control Section
Highway Section
Section, Township & Range
Existing roadway width, curb to curb
Left of CL
Proposed roadway width, curb to curb
Left of CL
Project No.
Datum
Right of CL Right of CL
Existing wearing surface (concrete, ACP, ACP w /membrane, LMC, epoxy, other)
Thickness
Existing drains to be plugged, modified, moved, other? Proposed overlay (ACP, ACP w /membrame, LMC, epoxy) Is bridge rail to be modified?
Yes
Thickness
No
Existing rail type Proposed rail replacement type Will terminal design “F” be required?
Yes
Will utilities be placed in the new barrier?
No Yes
No
Will the structure be overlayed with or after rail replacement?
With Rail Replacement
After Rail Replacement
Condition of existing joints Existing joints watertight?
Yes
No @ CL roadway
@ curb line Inch
Measure width of existing joint, normal to skew.
@ curb line Inch
Inch
Estimate structure temperature at time of joint measurement Type of existing joint Describe damage, if any, to existing joints Existing Vertical Clearance Proposed Vertical Clearance (at curb lines of traffic barrier)
Attachments Video tape of project
Sketch indicating points at which joint width was measured. Photographs of existing joints. Existing deck chloride and detamination data. Roadway deck elevations at curb lines (10-foot spacing) DOT Form 235-002A EF Revised 3/97
2.2-A2
August 1998
BRIDGE DESIGN MANUAL Appendix A Preliminary Design
Bridge Site Data Stream Crossings
Bridge Site Data Stream Crossings Region
Made By
Date
Bridge Information SR
Control Section
Bridge Name
Highway Section
Section, Township & Range
Name of Stream
Project No.
Datum
Tributary of
Elevation of W.S.
Stream Velocity
(@ date of survey)
(fps @ date of survey)
Depth of Flow (@ date of survey)
Max Highwater Elevation
@ Date
Normal Highwater Elevation
@ Date
Normal Stage Elevation
@ Date
Extreme Low Water Elevation
@ Date
Amount and Character of Drift Streambed Material Datum (i.e., USC and GS, USGS, etc.) Manning’s “N” Value (Est.)
Attachments Site Contour Map (See Sect. 7.02.00 Highway Hydraulic Manual) Highway Alignment and Profile (refer to map and profiles) Streambed: Profile and Cross Sections (500 ft. upstream and downstream) Photographs Character of Stream Banks (i.e., rock, silt, etc.) / Location of Solid Rock
Other Data Relative to Selection of Type and Design of Bridge, Including your Recommendations (i.e., requirements of riprap, permission of piers in channel, etc.)
DOT Form 235-001 EF Revised 3/97
August 1998
2.2-A3
BRIDGE DESIGN MANUAL Appendix A Preliminary Design
Preliminary Plan Checklist
Project__________________ SR______ Prelim. Plan by _____ Check by _____ Date_____ PRELIMINARY PLAN CHECKLIST PLAN ___Survey Lines and Station Ticks ___Survey Line Intersection Angles ___Survey Line Intersection Stations ___Survey Line Bearings ___Roadway and Median Widths ___Lane and Shoulder Widths ___Sidewalk Width ___Connection/Widening for Guardrail/Barrier ___Profile Grade and Pivot Point ___Roadway Superelevation Rate (if constant) ___Lane Taper and Channelization Data ___Traffic Arrows ___Mileage to Junctions along Mainline ___Back to Back of Pavement Seats ___Span Lengths ___Lengths of Walls next to/ part of Bridge ___Pier Skew Angle ___Bridge Drains, or Inlets off Bridge ___Existing drainage structures ___Existing utilities Type/Size, and Location ___New utilities - Type, Size, and Location ___Luminaires, Junction Boxes, Conduits ___Bridge mounted Signs and Supports ___Contours ___Top of Cut: Toe of Fill ___Bottom of Ditches ___Test Holes (if available) ___Riprap Limits ___Stream Flow Arrow ___R/W Lines and/or Easement Lines ___Points of Minimum Vertical Clearance ___Horizontal Clearance ___Exist. Bridge No. (to be removed, widened) ___Section, Township, Range ___City or Town ___North Arrow ___SR Number ___Bearing of Piers, or note if radial MISCELLANEOUS ___Structure Type ___Live Loading ___Undercrossing Alignment Profiles/Elevs. ___Superelevation Diagrams ___Curve Data ___Riprap Detail ___Layout Approval Block ___Notes to Region ___Names and Signatures ___Not Included in Bridge Quantities List ___Inspection and Maintenance Access
2.2-A4
ELEVATION ___Full Length Reference Elevation Line ___Existing Ground Line x ft. Rt of Survey Line ___End Slope Rate ___Slope Protection ___Pier Stations and Grade Elevations ___Profile Grade Vertical Curves ___BP/Pedestrian Rail ___Barrier/Wall Face Treatment ___Construction/Falsework Openings ___Minimum Vertical Clearances ___Water Surface Elevations and Flow Data ___Riprap ___Seal Vent Elevation ___Datum ___Grade elevations shown are equal to … ___For Embankment details at bridge ends … ___Indicate F, H, or E at abutments and piers TYPICAL SECTION ___Bridge Roadway Width ___Lane and Shoulder Widths ___Profile Grade and Pivot Point ___Superelevation Rate ___Survey Line ___Overlay Type and Depth ___Barrier Face Treatment ___Limits of Pigmented Sealer ___BP/Pedestrian Rail dimensions ___Stage Construction Lane Orientations ___Locations of Temporary Concrete Barrier ___Closure Pour ___Structure Depth/Prestressed Girder Type ___Conduits/Utilities in bridge ___Substructure Dimensions LEFT MARGIN ___Job Number ___Bridge (before/with/after) Approach Fills ___Structure Depth/Prestressed Girder Type ___Deck Protective System ___Coast Guard Permit Status ___Railroad Agreement Status ___Points of Minimum Vertical Clearance ___Cast in Place Concrete Strength RIGHT MARGIN ___Control Section ___Project Number ___Region ___Highway Section ___SR Number ___Structure Name
August 1998
BRIDGE DESIGN MANUAL Appendix A Preliminary Design
January 1991
Bridge Stage Construction Comparison
2.3-A1
BRIDGE DESIGN MANUAL Criteria Analysis
Contents Page
3.0 3.1 3.1.1 3.1.2 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.3 3.4 3.5 3.5.1 3.5.2 3.6 3.6.1 3.6.2 3.6.3 3.6.4 3.6.5 3.7 3.8 3.8.1 3.8.2 3.9 3.9.1 3.9.2
Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Philosophy of Analysis Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Analysis Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Frame Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Member and Frame Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Partial Fixity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Development of F.E.M.s and Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Influence Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sidesway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trusses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Computer Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Discussion of Computer Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . List of Programs Available . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Analysis Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Energy Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Castiglano . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Virtual Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Buckling Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Finite Element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dynamic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Special Analysis Problems by Bridge Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Suspension bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cable Stayed Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Special Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Skew . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Footing Deflections and Rotations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Appendix A 3.0-A1 3.0-A2 3.0-A3 3.0-A4 3.0-A5 3.0-A6 3.0-A7 3.0-A8
3.1-1 1 1 1 * * * 3.2-1 * * * * * * * * * * * * * * * * * * * *
Concentrated Load Coefficients — General Concentrated Load Coefficients — Case I Fixed End Moment Coefficient Chart Influence Lines — Two Equal Spans Coefficients and Factors for Double Tapered Members Stiffness Factors for Tapered Members Carry Over Factors for Tapered Members Fixed End Moments for Tapered Members
*Indicates sections not issued to date. 3-CON:V:BDM3
July 1994
3.0-i
BRIDGE DESIGN MANUAL Criteria Analysis 3.0
Analysis
3.1
General Considerations
3.1.1
Philosophy of Analysis Procedures
General Considerations
For the design of concrete bridges, in distribution of moments, generally use the gross moment of inertia of the concrete superstructure. In lieu of including the transformed area of steel for columns or other compression members, 120 percent of the gross moment of inertial of columns and other compression members may generally be used.
3.1.2
Analysis Methods The maximum live load deflection computed shall be in accordance with AASHTO except that the maximum live load deflection in a span shall not exceed 1/1000 and for a cantilever 1/375, regardless of whether the bridge is used by pedestrians.
3-1:V:BDM3
July 1994
3.1-1
BRIDGE DESIGN MANUAL Criteria Analysis 3.2.1
Theory (Vacant)
3.2.2
Member and Frame Factors (Vacant)
3.2.3
Partial Fixity
Frame Analysis
In general, assume 50 percent fixity of footings except footings on rock shall be 100 percent fixed. For frame analysis, the point of fixity shall normally be taken to be at the approximate center line of footing. For column design, Volume 2 Sheets 9-220 through 9-225 shall be consulted. This shall hold for footings with or without seals. Where superstructures are supported directly on piles, for analyses of the structure the piles may be assumed fixed at a point 5 feet to 10 feet in the ground. For flat slab bridges supported on piling, the piles shall be assumed pinned at the tops. For design of structures with large diameter shafts see Section 9.8 For one column piers assume the footing fully fixed in the direction transverse to the roadway. For loads on one column piers assume the pier acts transversely as a simple cantilever, fixed at the footing, with no allowance for torsional, or lateral stiffness of the superstructure.
3-2:V:BDM3
July 1994
3.2-1
BRIDGE DESIGN MANUAL Appendix A Analysis
Concentrated Load Coefficients — General
July 1994
3.0-A1
BRIDGE DESIGN MANUAL Appendix A Analysis
3.0-A2
Concentrated Load Coefficients — Case I
July 1994
BRIDGE DESIGN MANUAL Appendix A Analysis
Fixed End Moment Coefficient Chart
July 1994
3.0-A3-1
BRIDGE DESIGN MANUAL Appendix A Analysis
3.0-A3-2
Fixed End Moment Coefficient Chart
July 1994
BRIDGE DESIGN MANUAL Appendix A Analysis
Influence Lines — Two Equal Spans
July 1994
3.0-A4
BRIDGE DESIGN MANUAL Appendix A Analysis
Coefficients and Factors for Double Tapered Members
July 1994
3.0-A5-1
BRIDGE DESIGN MANUAL Appendix A Analysis
3.0-A5-2
Coefficients and Factors for Double Tapered Members
July 1994
BRIDGE DESIGN MANUAL Appendix A Analysis
Stiffness Factors for Tapered Members
July 1994
3.0-A6
BRIDGE DESIGN MANUAL Appendix A Analysis
3.0-A7
Carry Over Factors for Tapered Members
July 1994
BRIDGE DESIGN MANUAL Appendix A Analysis
Fixed End Moments for Tapered Members
July 1994
3.0-A8-1
BRIDGE DESIGN MANUAL Appendix A Analysis
3.0-A8-2
Fixed End Moments for Tapered Members
July 1994
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Contents Page
4.0 4.1 4.1.1 4.1.2
Loads and Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dead Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Distribution to Superstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Distribution to Substructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3 Wind Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.4 Wind on Live Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.5 Earthquake Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.6 Other Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Thermal, Shrinkage, and Prestressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Buoyancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Centrifugal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Force from Stream Current, Floating Ice, and Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Load Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Combination of Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2 Load Factor Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.3 Service Load Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Application of Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 Dead Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.2 Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.3 Wind Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.4 Earthquake Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Foundation Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Procedure Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Spread Footings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3 Pile Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Lateral Spring Input from P-Y Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Lateral Spring Input to Dynamic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Vertical Springs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Stiffness Matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. GPILE Computer Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.99 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix A 4.4-A1-1 Foundation Design Seismic Flow Chart 4.4-A2 Peak Ground Acceleration Map Appendix B 4.3-B1 Basic Truck Loading 4.3-B2 Common Response Modification Factors 4.3-B3 Seismic Analysis Example 4.4-B1 Spring Constants Evaluation Example
4.1-1 1 1 1 1 1 3 3 3 3 4 4 4 4 5 4.2-1 1 1 3 4.3-1 1 1 4 4 4.4-1 1 1 1 1 4 7 8 8 4.99-1
P:DP/BDM4
August 1998
4.0-i
BRIDGE DESIGN MANUAL Criteria Loads and Loading 4.0
Loads
Loads and Loading AASHTO loading specifications shall be the minimum design criteria used for all bridges.
4.1
Loads
4.1.1
Dead Loads Use values in AASHTO except as herein modified: Reinforced Concrete — 160 pounds per cubic foot. D.L. Forms in Top Slab of Concrete Box Girders — 5 pounds per square foot of cell area.
4.1.2
Live Loads A. General Live load design criteria is specified in the lower right corner of the bridge preliminary plan sheet. The Bridge Projects Unit determines this criteria using the following guideline: • HS 25 — New bridges on the interstate or state system and bridge widenings involving addition of substructure. • HS 20 — Bridge widenings with no addition of substructure. • HS 15 — Detour bridges. Use values described in AASHTO. Design for HS25 loading by multiplying HS20-44 axle loads by 1.25. The loading consisting of two 24K axles at 4-foot centers sometimes governs for short span bridges. See Figure 4.3.2-1 for illustration of this “alternative” loading. See Figures 4.3.2-2 and 3 for “L” value to use in the formula in Section 4.3.2. Figure 4.3.2-2 illustrates determination of the “L” length of the member under consideration. For beams and girders, use span length center to center of supports. For cantilevers, use length from center of support to farthest load on cantilever. See Figure 4.3.2-2 for illustration. B. Distribution to Superstructure 1.
Integral Deck Precast Sections The Live Load Distribution factor for Bulb Tee, Single Tee, and Double Tee bridges shall be as determined through use of the “DISTBM” computer program. (See Bridge Computer Programs Manual.) The AASHTO Specifications should be used for Rib Deck Bridges and the beam types listed therein. For Rib Deck Bridges use a K value of 2.2. Examples of beam types are shown on Figure 4.1.2-1.
2.
Concrete Box Girders The value for the number of traffic lanes to be used in the concrete box girder superstructure design shall be determined by dividing the entire roadway slab width by 14. Use fractional lanes, rounding to the nearest tenth of a foot, if applicable. Roadway slab widths of less than 28 feet shall have two design lanes. No reduction factor will be applied to the superstructure for multiple loadings.
August 1998
4.1-1
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Loads
Beam Types Figure 4.1.2-1
4.1-2
August 1998
BRIDGE DESIGN MANUAL Criteria Loads and Loading 3.
Loads
Other Types See AASHTO Specifications.
C. Distribution to Substructure The value for the number of traffic lanes to be used in the substructure design shall be determined by dividing the entire roadway slab width by 12. No fractional lanes shall be used. Roadway slab widths of less than 24 feet shall have a maximum of two design lanes. A reduction factor will be applied in the substructure design for multiple loadings in accordance with AASHTO. The following percentages of the resulting live loading shall be used: Number of Lanes Loaded Two Lanes Three Lanes Four Lanes or More
4.1.3
Percent 100 90 75
Wind Loads AASHTO load combinations for wind are based on probability of simultaneous load occurrence. The basic wind loads result from 100 mph wind, which produces 75 psf on trusses and arches, 50 psf on girders and beams, and 40 psf on substructures. This wind is assumed to act on the structure when live load is not present. A 30 mph wind (0.3 × 100, or a 70 percent reduction from basic) is included in Groups III and IV, and is assumed to act when live load is present. The forces tending to overturn a structure are represented by an upward high wind pressure of 20 psf acting on the plan view area, for Groups II, V, and IX. A moderate wind pressure of 6 psf is used for Groups III and VI. The force is applied at the windward quarter point of the transverse superstructure.
4.1.4
Wind on Live Load A moderate wind force is assumed to act on the live load itself, represented by a live load acting 6 feet above the roadway surface, both transversely and longitudinally. This force is computed by multiplying the bridge length tributary to a particular member by 0.1 for transverse and 0.04 for longitudinal direction.
4.1.5
Earthquake Loads a.
Design for earthquake shall be in accordance with Division 1-A, Seismic Design of the 1996 AASHTO Standard Specifications for Seismic Design of Highway Bridges.
b.
The Multimode Spectral Method of dynamic analysis described in the AASHTO Specifications shall be used for most continuous bridges. The SEISAB computer program can be used to analyze most common bridges. The GTSTRUDL dynamic analysis system is capable of handling a larger range of structures.
c.
The Single Mode Spectral Method may be used in certain cases, as described in the AASHTO Specifications.
d.
Use the USGS Peak Ground Acceleration map (Appendix 4.4-A2, 10 percent Probability of Exceedance in 50 Years) to obtain an acceleration coefficient for preliminary design. The project Foundation Report will contain the acceleration coefficient to use in the final design of a bridge. When using Appendix 4.4-A2, interpolate between contours to find the value to use for particular site, and round to the nearest 1 percent of gravity (g). In general, Appendix 4.4-A2 can also be used for
August 1998
4.1-3
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Loads
bridge seismic retrofit designs. However, seismic evaluation and retrofitting of older bridges can sometimes result in excessive costs (the retrofit costs are not consistent with the benefit gained). In these situations, the Bridge Design Engineer should be consulted for direction.
4.1.6
e.
It is recommended that temporary (detour) structures shall be designed for a seismic acceleration coefficient equal to 0.5 x the acceleration coefficient for a permanent structure. All other requirements of the AASHTO Specifications for Seismic Design of Highway Bridges shall apply. Seismic Performance Category shall be based on the magnitude of the reduced acceleration coefficient.
f.
The Geotechnical Engineer should be consulted when determining the soil type to be used in the seismic analysis.
Other Loads A. Thermal, Shrinkage, and Prestressing Member loadings are induced by movements of the structure and can result from several sources. Movements due to temperature changes are calculated using coefficients of thermal expansion of 0.000006 ft/ft per degree for concrete and 0.0000065 ft/ft per degree for steel. Reinforced concrete shrinks at the rate of 0.0002 ft/ft. Refer to AASHTO and Bridge Design Manual Chapters 6, 8, and 9 for guidance on computation and application of these force types. B. Buoyancy The effects of submergence of a portion of the substructure is to be calculated, both for designing piling for uplift and for realizing economy in footing design. C. Centrifugal Centrifugal forces are included in all groups which contain vehicular live load. They act 6 feet above the roadway surface and are significant where curve radii are small or columns are long. They are radial forces induced by moving trucks. See AASHTO for force equation.
4.1-4
August 1998
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Loads
D. Force from Stream Current, Floating Ice, and Drift In designing for stream flow force on piers, a reasonable area of drift or floating ice must be determined, considering the stream or river characteristics (check with the Hydraulics Unit). Water depth and pier spacing will partly determine drift areas.
W.S. =
Water surface as defined by the Hydraulics Unit
SF
=
PdAd + PpAp
Ad
=
Area of drift or floating ice = D x E
Ap
=
Area of pier below ice = B x C. Where the pier is skewed to the stream, flow C equals the width of the column normal to the stream flow.
V
=
Velocity of water (ft/sec)
Pd
=
Pressure on drift (psf) = 1.38 V2
Pp
=
Pressure on pier (psf) = KV2
In the absence of other data, the maximum values of D and E shall be 10 feet and 50 feet, respectively. Water Related Forces Figure 4.1.6-1
DP:BDM4
August 1998
4.1-5
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Load Combinations
4.2
Load Combinations
4.2.1
Combination of Loads Group numbers represent various combinations of loads and forces which may act on a structure. Group loading combinations for both Load Factor and Service Load Design are defined by the following equation: Group (N) = γ[βd D + βp PS + βL (L+I) + βc CF + βE E + βD B + βs SF + βw W + βwL WL + βL LF + βR (R + S + T) + βEQ EQ + βICE ICE] where: N γ βN D PS L I E B W WL LF CF R S T EQ SF ICE
= = = = = = = = = = = = = = = = = = =
Group Number General Factor Specific Factor Dead Load (including overburden) Prestress Load* Live Load Live Load Impact Earth Pressure (Lateral, only) Buoyancy Wind Load on Structure Wind Load on Live Load — 100 pounds per linear foot of span Longitudinal Force from Live Load Centrifugal Force Rib Shortening Shrinkage Temperature Earthquake Stream Flow Pressure Ice Pressure
*PS = Forces and moments transferred from members containing post-tensioning steel to other members upon application of the post-tensioning force. Terms in the general equation that do not contribute to a particular combination are represented by zeros in the table.
4.2.2
Load Factor Coefficients LFD requires basic design loads or related internal moments and forces to be increased by specified load factors, γ and β. The γ factor is applied for stress control. Its common value is 1.3, which enables use of 77 percent of the ultimate capacity. The 30 percent increase in design load represented by the factor is intended to account for variations in weight, reinforcement placement, structural behavior, and calculation of stress. The β factor is a measure of the accuracy of load prediction and the probability of simultaneous application of loads in a combination. Table 4.2.2-1 contains the terms and factors required to meet AASHTO Load Factor Design.
August 1998
4.2-1
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Load Combinations
Column Design βD = 0.75 or bD = 1.0, whichever governs. Flexural and Tension Members βD = 1.0 βE = 1.0 Footing Bearing Pressure and Internal Footing Stresses βD = 0.75 or βD = 1.0 βE = 1.0 Footing Stability and Sliding βD = 0.75 or βD = 1.0, whichever governs. βE = 0.4 or βE = 1.3, whichever governs. Notes: 1.
For footing design, check Basic Loading Combination in accordance with BDM Section 9.5.1A3.a.
2.
For rigid frame design, see BDM Section 9.3.4.E.
3.
Check stability for all group loadings in accordance with BDM Section 9.5.1A3.b.
4.
Group 1A load combination shall be applied only with live loadings less than HS 20 or H 20. See AASHTO.
*Applies if design loads are already factored, such as in cases where MDes = 1.0 ML + 0.3 MT or MDes = 0.3 ML + 1.0 MT are used. Table of Coefficients γ and β For Load Factor Design Table 4.2.2-1
4.2-2
August 1998
BRIDGE DESIGN MANUAL Criteria Loads and Loading 4.2.3
Load Combinations
Service Load Coefficients Table 4.2.3-1 contains the terms and factors required to meet AASHTO Service Load Design. The allowable percentage of the basic unit stress is given in the right hand column of the table.
Footing Bearing Pressure and Internal Footing Stresses βE = 1.0 Footing Stability and Sliding βE = 0.5 or βE = 1.0, whichever governs. Notes: 1.
For culvert loading, see AASHTO.
2.
No increase in allowable unit stresses shall be permitted for members or connections carrying wind load only. Table of Coefficients γ and β For Service Load Design Table 4.2.3-1
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August 1998
4.2-3
BRIDGE DESIGN MANUAL Criteria Loads and Loading 4.3
Application of Loads
4.3.1
Dead Loads
Application of Loads
Dead load is commonly applied to supports by assuming that it acts along each girder line.
4.3.2
Live Loads The three types of live loadings ordinarily applied to a bridge when checking for maximum stresses in its components are illustrated in AASHTO and Figure 4.3.2-1. The standard H-S truck represents common vehicles. The lane load consists of combinations of uniform and concentrated loads which represent three lighter trucks spaced close together. The alternative loading represents certain heavy military vehicles. The loading type governing the design depends on the structure configuration. For example, truck loading governs for maximum moment in simple spans shorter than 145 feet and lane loading controls for longer spans. In continuous spans, lane loading governs for maximum negative moment, except for spans shorter than 45 feet, in which truck loading will govern. The maximum positive moment in continuous spans is usually produced by using lane loading, for span lengths of over about 110 feet. Alternative loading governs in certain short span situations. Figures 4.3.2-2 and 4.3.2-3 illustrate application of loads to produce maximum stresses in various span arrangements. Appendix 4.3-B1 illustrates calculation of reactions and maximum moments in a simple span. Impact is figured using the following formula: I=
50 L + 125
Where L is the loaded portions of the spans.
Alternative (Military) Loading Figure 4.3.2-1
August 1998
4.3-1
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Application of Loads
Application of Loads Figure 4.3.2-2
4.3-2
August 1998
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Application of Loads
Application of Loading Figure 4.3.2-3
August 1998
4.3-3
BRIDGE DESIGN MANUAL Criteria Loads and Loading 4.3.3
Application of Loads
Wind Loads Wind loads acting on the superstructure are based on the profile presented to the wind, the height of which usually consists of the girder depth and traffic barrier height.
4.3.4
Earthquake Loads Bibiography 1 through 4 contain several examples of applying earthquake loads to bridges. This section serves to amplify some analysis concepts. Load factors applied in the Group VII combination are based on two concepts: 1.
Full utilization of the elastic capacity of a particular element or member.
2.
Taking advantage of the ductility or redundancy of the structure to absorb the energy released in an earthquake and keep the structure intact. Two typical AASHTO load case equations are: MEQ MEQ
= or =
1.0
ML
+
0.3
MT
1.0
ML
+
1.0
MT
Where the moments are: MEQ ML MT
= = =
Earthquake Longitudinal Transverse
These equations are intended to satisfy concept 1. The SEISAB computer program prints out solutions to the two equations as load cases 3 and 4. Concept 2 is handled through use of the “R” factor. It appears in the factored loading equation: Mu
=
1.0 (MDL + MEQ/R)
The Guide Specification lists values for “R” for various structural components and types of supports. Some common examples are: • Single column bents, considered ductile but nonredundant, R = 3 for both directions. • Multi-column bents, considered ductile and redundant, R = 5 both ways. • Wall-type piers, less ductile than single column bents, often having R = 2 for transverse behavior and R = 3 longitudinally. • Footings, R = 1 for seismic performance Categories C and D and R = Rcol for SPC B. Higher values are used than for columns and crossbeams because below ground structural damage is difficult to spot and repair. Plastic hinging moments are often less than those produced using an R of 1, so that some economy may be realized. • Bearing type connections and stops, R = 0.8, due to lack of ductility and redundancy and because they serve to prevent large displacements. See Appendix 4.3-B2-1 and 2 for illustrations of common piers and appropriate factors to apply to the members.
4.3-4
August 1998
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Application of Loads
In order to design structures to survive the forces and strains resulting from earthquake motion, the following factors need to be considered: • The proximity of the site to known active faults and the historical record of activity. • The seismic response of the soil at the site. • The dynamic response characteristics of the total structure. See Appendix 4.3-B3-1 through 3 for a general discussion of a seismic analysis.
4-3:P:BDM4
August 1998
4.3-5
BRIDGE DESIGN MANUAL Criteria Loads and Loading 4.4
Foundation Modeling
Foundation Modeling Proper foundation modeling for earthquake loads is necessary because misinterpreted AASHTO Specifications can lead to a wide range of member sizes. Realistic models will likely produce savings in material, especially when determining loads to apply to a substructure. Analysis is an iterative process which converges to an acceptable design.
4.4.1
Procedure Summary Following is a workable procedure for analysis:
4.4.2
4.4.3
a.
Assume the foundation as fixed (unless you know otherwise). Use SEISAB or GTSTRUDL to perform a dynamic analysis to determine initial loading.
b.
If the support is not founded in rock, multiply the forces from the fully fixed model by 0.85 for the initial trial design. Otherwise, use the fully fixed forces for the trial.
c.
Determine a preliminary footing size, pile size, and arrangement, as applicable to the type of support.
d.
Determine foundation springs as outlined in this section and Section 4.4.2. If pile support is being used, see Section 4.4.3.E.
e.
Rerun the dynamic model with springs included.
f.
Compare loads and deflections using the same range used to determine the springs.
g.
Redesign the footing, piles, adjust the springs, etc., until tolerable convergence is attained.
Spread Footings a.
You may apply load factor column moments from groups other than Group VII and column plastic hinging moments for a first trial footing configuration. Then determine soil spring constants using the footing plan area and depth of embedment. Assuming a shear wave velocity value, consult a Foundation or Geotechnical Engineer for an appropriate value.
b.
Appendix 4.4-B1 through 4 illustrate a procedure to determine soil spring constants for spread footings.
Pile Foundations A. Lateral Spring Input from P-Y Curves Spring constants that represent pile supports may be obtained using a procedure which begins by applying moments (as described in Section 4.4.1A) to an assumed footing and pile configuration. P-Y curves from the foundation report may be input to the LPILE1 computer program to derive the initial spring constants. The spacing between pile centers is often about 4 times the pile diameter (D), which means that each pile in the group may deflect more than if it were acting alone. Apply efficiency factors, if provided on the soils report, to quantify that difference. If information is not available, use the following table to estimate values.
August 1998
4.4-1
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Foundation Modeling
Efficiency Factor Table 4.4.3-1 For driven piles, the following factors apply: Contact the Olympia Service Center Materials Lab to verify any assumptions. The LPILE1 computer program will generate P-Y curves, or the user can input them. To obtain generated curves, input a modulus of subgrade reaction (K), and a soil shear strength (C) which are the values taken from the soils report multiplied by the efficiency factor. To figure P-Y curves for input, multiply the P-Y values from the soils report by the efficiency factor. For a typical soil, the relationship between its normalized resistance value and friction angle is defined by the curve in Figure 4.4.3-1. The friction angle could be adjusted for efficiency and input to LPILE1 by following these steps:
4.4-2
1.
Begin at the coordinate of the natural friction angle (36°).
2.
Read across to the normalized resistance (61).
3.
Multiply the resistance by the efficiency reduction factor, i.e., 61 (0.5) = 31.
4.
Read across from the reduced value to obtain the adjusted friction angle (31°).
5.
Input the φ value to LPILE1.
August 1998
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Foundation Modeling
Friction Angle (φ) PS = Ka (tan8B-1) + Ko tan φ tan 4B bγx
PS
=
Soil Resistance on Pile Element
b
=
Pile Width
g
=
Soil Unit Weight
X
=
Depth to Pile Element
N
=
Step in Example
B
=
45° + φ/2
Ka
=
tan2(45° – φ/2)
Ko
=
1 – Sin φ Figure 4.4.3-1
August 1998
4.4-3
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Foundation Modeling
B. Lateral Spring Input to Dynamic Analysis Lateral spring constants can be generated for input to SEISAB (or GTSTRUDL) by using LPILE1 and two types of loading. Case 1 — Applied Lateral Load — See Figure 4.4.3-2(A). Apply a lateral load (F) to the model of a pile, and restrain its top against rotation. The load produces a deflected shape with the top deflection being ∆. A moment (M) is also induced. F and M may be plotted against ∆ to produce two curves. The spring constants are defined as slopes of the curves, and their calculation and SEISAB nomenclature are given by the equations in Figure 4.4.3-2(A). Make enough LPILE1 runs to define a linear range along the lateral force versus a deflection curve. Vary axial loads, to bracket the values expected from the dynamic analysis (i.e., SEISAB results). Include negative axial loads to represent anticipated tension due to uplift effects. Case 2 — Applied Moment — See Figure 4.4.3-2(B). Apply a moment (M) to the pile model, restraining the pile top against translation. Calculate the pile top rotation (φ) from the LPILE1 output by dividing the deflection at the bottom of the top increment (∆1) by the increment length (H1). The spring constants are defined as slopes of the curves, and they are calculated using the equations in Figure 4.4.3-2(B). A rapid way to approximate the slope of any curve is to select a point at half of the ultimate lateral force or moment capacity of the pile. Note that the off-diagonal terms must be equal and opposite in sign. Figure 4.4.3-3 contains examples of spring calculation from LPILE1 output.
4.4-4
August 1998
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Foundation Modeling
Figure 4.4.3-2A
Figure 4.4.3-2B
August 1998
4.4-5
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Foundation Modeling
Loading Number 1 Boundary condition code Lateral load at the pile head Slope at the pile head Axial load at the pile head
= = = =
2 0.250D+05 lbs = 25 K applied 0.000D+00 in/in 0.758D+05 lbs
X
Deflection
Moment
Shear
In
In
Lbs-In
Lbs
*****
**********
********** ********** **********
********** **********
0.00
0.267D+01
-0.383D+07
0.270D+05
0.250D+05
0.000D+00
Total Stress Lbs/In**2
Flexural Rigidity Lbs-In**2
0.392D+11
=25K
=2.67″ KF1F1 = KF3F3 =
Soil Reaction Lbs/In
K 25K = 112 (2.67in / 12 in / ft ) ft
(A) Loading Number 1 Boundary condition code Deflection at the pile head Moment at the pile head Axial load at the pile head
= = = =
4 0.000D+00 in 0.391D+07 in-lbs = 391 K-in applied 0.103D+06 lbs
X
Deflection
Moment
Shear
In
In
Lbs-In
Lbs
*****
**********
********** ********** **********
********** **********
0.00 28.04
0.000D+00 -0.237D+00
0.391D+07 0.340D+07
0.281D+05 0.247D+05
0.189D+05 -0.186D+05
Soil Reaction Lbs/In
0.000D+00 0.208D+02
Total Stress Lbs/In**2
Flexural Rigidity Lbs-In**2
0.392D+11 0.392D+11
0.237″ = ∆1 28.04″ = H ∆1
f = Tan–1 H = Tan–1 1
0.237 = 0.48426° 28.04
or = 0.00845 rad (B) Sample LPILE1 Output Figure 4.4.3-3
4.4-6
August 1998
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Foundation Modeling
C. Vertical Springs Vertical spring constants, Kv (or KF2F2) can be calculated from the following equations: Point bearing pile: Kv =
AE L
where, A E L
= = =
Cross sectional area Young’s modulus Length
Pile having constant skin friction: Kv =
2AE L
Pile linearly varying skin friction: Kv =
3AE L
Pile partially embedded in the soil:
August 1998
1.
AE Kv = 1 − F L 2
2.
AE Kv = 1 − 2 F L 3
4.4-7
BRIDGE DESIGN MANUAL Criteria Loads and Loading
Foundation Modeling
Torsional (M/φ) spring constants for individual piles are based on the strength of the pile only. The torsional resistance is given by the following equation: M/φ
=
T/φ
=
JG/L
where, G J L
= = =
0.4 E Torsional Moment of Inertia length of pile
D. Stiffness Matrix Eight individual pile stiffness terms should be put into Seisab, which forms a {6 × 6} matrix as shown below:
F1 F2 F3 M1 M2 M3
F1
F2
F3
M1
M2
M3
KF1F1
0 KF2F2
0 0 KF3F3
0 0 -KF3M1 KM1M1
0 0 0 0 KM2M2
KF1M3 0 0 0 0 KM3M3
"Symmetrical"
KF1M3 is cross-coupling term P/φ. -KF3M1 is cross-coupling term M/d. Note that the two have opposite signs. E. GPILE Computer Program If a large number of piles is required per footing, to reduce Seisab input/output, individual springs can be used in the GPILE computer program. The output will contain a {6 × 6} stiffness matrix for the pile group which can be used to model the foundation in SEISAB. GPILE input includes pile configuration and spring constants. The program also computes individual pile loads and deflections from a set of input loads. GPILE can be used in conjunction with the plastic hinging moments, transmitted from the column, to converge on an acceptable pile configuration.
4-4:P:BDM4
4.4-8
August 1998
BRIDGE DESIGN MANUAL Criteria Loads and Loading 4.99
Bibliography
Bibliography 1.
AASHTO, Standard Specifications for Design of Highway Bridges, 1996, Division 1-A Seismic Design.
2.
Imbsen, R. A., Seismic Design of Highway Bridges, FHWA Workshop Manual, January 1981, DOT-FH-11-9426.
3.
FHWA/RD-83/007 Seismic Retrofitting Guidelines for Highway Bridges, December 1983.
4.
FHWA-IP-87-6, Seismic Design and Retrofit Manual for Highway Bridges, May 1987.
5.
California Department of Transportation, Bridge Design Practice, 1983.
6.
Chen, R. L., Pile Foundation Modeling for Bridge Dynamic Response Analysis, unpublished paper available in WSDOT Bridge and Structures Design, April 1987.
7.
Engineering Computer Corporation, SEISAB-I, Workshop Manual, October 1984 and August 1985.
8.
Reese, Lymon C., Documentation of Computer Program LPILE1, report for Ensoft, Inc., The University of Texas at Austin, 1985.
9.
AASHTO, Standard Specifications for Highway Bridges, 1996.
10. Washington State Department of Transportation, Bridge Computer Programs Manual, GPILE and DISTBM. 11. Washington State Department of Transportation, 1996, USGS National Seismic Hazards, Mapping Project. 12. Hart Crowser, Subsurface Explorations and Design Phase Geotechnical Engineering Study, SR 90, Seattle Access, Volume 111, September 1986, J-712-50. 13. Federal Highway Administration, Manual on Design and Construction of Driven Pile Foundations, FHWA-DD-66-1, Revision 1. 14. Imbsen & Associates, FHWA, Seismic Design of Highway Bridges Training Course Participant Workbook, February 1989. 15. FHWA-86/103, Seismic Design of Highway Bridges, Vol. II: Example problems and Sensitivity Studies, June 1986.
4-99:P:BDM4
August 1998
4.99-1
BRIDGE DESIGN MANUAL Appendix A Loads and Loading
August 1998
Foundation Design Seismic Flow Chart
4.4-A1-1
BRIDGE DESIGN MANUAL Appendix A Loads and Loading
4.4-A1-2
Foundation Design Seismic Flow Chart
August 1998
BRIDGE DESIGN MANUAL Appendix A Loads and Loading
August 1998
Foundation Design Seismic Flow Chart
4.4-A1-3
BRIDGE DESIGN MANUAL Appendix A Loads and Loading
4.4-A1-4
Foundation Design Seismic Flow Chart
August 1998
BRIDGE DESIGN MANUAL Appendix A Loads and Loading
August 1998
Foundation Design Seismic Flow Chart
4.4-A1-5
BRIDGE DESIGN MANUAL Appendix A Loads and Loading
4.4-A1-6
Foundation Design Seismic Flow Chart
August 1998
BRIDGE DESIGN MANUAL Appendix A Loads and Loading
August 1998
Foundation Design Seismic Flow Chart
4.4-A1-7
BRIDGE DESIGN MANUAL Appendix A Loads and Loading
4.4-A1-8
Foundation Design Seismic Flow Chart
August 1998
BRIDGE DESIGN MANUAL Appendix A Loads and Loading
August 1998
Foundation Design Seismic Flow Chart
4.4-A1-9
BRIDGE DESIGN MANUAL Appendix A Loads and Loading
4.4-A1-10
Foundation Design Seismic Flow Chart
August 1998
BRIDGE DESIGN MANUAL Appendix A Loads and Loading
August 1998
Peak Ground Acceleration Map
4.4-A2
BRIDGE DESIGN MANUAL Appendix B Loads and Loading
Basic Truck Loading
Basic Truck Loading HS25
August 1998
4.3-B1
BRIDGE DESIGN MANUAL Appendix B Loads and Loading
August 1998
Common Response Modification Factors
4.3-B2-1
BRIDGE DESIGN MANUAL Appendix B Loads and Loading
4.3-B2-2
Common Response Modification Factors
August 1998
BRIDGE DESIGN MANUAL Appendix B Loads and Loading
Seismic Analysis Example
A recent analysis of a bridge on I-90 in the Mercer Slough area near Bellevue provides the following example: The deep soft soil at the site is classified as “Type III” from the AASHTO Specifications. An acceleration coefficient of 0.25, see Figure 4.1.5-1, was selected as appropriate. The acceleration spectrum shown in Appendix 4.3-B3-2 was used to load the bridge. The results which SEISAB calculated for the first 6 modes of oscillation appear in Appendix 4.3-B3-3. The CS values in the table relate directly to the response periods of the various modes as solutions to the equation: CS = 1.22AS /3 T
where: A
=
The acceleration coefficient
S
=
The soil profile coefficient (1.5 in this case)
T
=
The period of vibration of the bridge, the time it takes for one cycle of oscillation
In an undamped, single degree of freedom system, the natural period is defined as: T= π
M K
where: M
=
The mass involved
K
=
The spring constant
See Bibliography 1 and 7 for further comments and procedures. CS, the elastic seismic response coefficient, is the percentage of a gravity force which is applied to the bridge for a particular mode. The participation factors indicate that modes 1 and 3 contribute most heavily to the design forces. In this case, the ground sends 0.25 g and the bridge receives about 0.50 g. The 0.50 g applied, divided by R = 5, translates to 0.1 g when figuring design moments for a multiple column bent. Design shears would be the lesser of the values produced by 0.50 g and the shears associated with plastic hinging moments. Since the column reinforcement may yield when the 0.1 g level is reached, the energy remaining will be redistributed to the remainder of the bridge. The main column reinforcement must be adequately confined by ties or spirals to allow redistribution to occur while maintaining structural integrity.
P:DP/BDM4
August 1998
4.3-B3-1
BRIDGE DESIGN MANUAL Appendix B Loads and Loading
Seismic Analysis Example
Example Seismic Analysis
4.3-B3-2
August 1998
BRIDGE DESIGN MANUAL Appendix B Loads and Loading
Seismic Analysis Example
Example Seismic Analysis (Continued)
August 1998
4.3-B3-3
BRIDGE DESIGN MANUAL Appendix B Loads and Loading
Spring Constants Evaluation Example
Given Data • Cohesionless soil – Poisson’s ratio = 0.33 = µ • Soil density – 120 pcf = σ • VS = shear wave velocity = 1,500 ft/sec Solution: Shear Modulus 120 lb/ft 3 (1, 500 ft/sec)
2
G= °Vs2 = 32.2 ft/sec 2 1000 Lb/ K ( ) Vertical Stiffness L/W; ßZ ;
1.0 2.12
L/W =
KZ =
1.5 2.14
18 = 1.20 15
2.0 2.18
3.0 2.26
5.0 2.44
10.0 2.82
ßZ = 2.13
β Z G LW K 2.13 × 8385 18 × 15 = = 438,000 1− µ ft 1 − 0.33
Embedment Factor ro =
KW =- 9.27′ π
H 6 ro = 9.27 = 0.65
August 1998
4.4-B1-1
BRIDGE DESIGN MANUAL Appendix B Loads and Loading
Spring Constants Evaluation Example
Vertical Stiffness — Modified KZH = 1.36 KZ = 1.36 × 438,000 = 596,000 kips/ft = KFY Horizontal Stiffness L = 1.20 < 5 W
ßx = 2.0
KX = ßX (1 – µ)
G LW
= 2.0 (1 – 0.33)
8385
(See page 6-37 of Bilbliography 2 for explanation.)
18 × 15 = 185,000 K/ft
Assuming that the horizontal embedment effect is the same as the vertical. Horizontal Stiffness — Modified KXH = 1.85 × 105 1.36 = 2.5 × 105 K/ft = KFX = KFZ
4.4-B1-2
August 1998
BRIDGE DESIGN MANUAL Appendix B Loads and Loading
Spring Constants Evaluation Example
Rocking Stiffness Long Direction R=
d = 1.20 c
R; ßψ;
c = 7.5′
d = 9′
ßψ = 0.52
0.2 0.4
0.5 0.45
1.0 0.5
2.0 0.6
4.0 0.8
6.0 0.95
8.0 1.1
(8G cd ) 2
Kψ = ßψ
=
1− µ
K − ft 0.52 × 8 × 8385 × 7.5 × 9 2 = 3.2 × 107 rad 1 − 0.33
KH = 1.36 (3.2 × 107) = 4.3 × 107
K − ft = KMZ rad
Short Direction R=
c = 0.83 d
Kψ = ßψ
=
ßψ = 0.48
(8G)dc 2 1− µ
= 2.4 × 107
K − ft rad
0.48 × 8 × 8385 × 9 × 7.52 1 − 0.33
Kψ H = 1.36 (2.4 × 107) = 3.3 × 107
K − ft rad
Torsional Stiffness rc = Kθ =
4
16cd(c 2 + d 2 ) 6π
=4
16 × 7.5 × 9(7.52 + 9 2 ) 6π
16 16 K − ft Gre3 = × 8385 × 9.423 = 3.7 × 107 3 3 rad
Kθ H = 1.36 (3.7 × 107) = 5.0 × 107
K − ft = KMY rad
Appendix 4.4-B1-4 depicts the footing from the example in spring matrix form. The nomenclature is general, and is used for GTSTRUDL input (GTSTRUDL 4.2.2d contains a similar matrix using SEISAB nomenclature).
August 1998
4.4-B1-3
BRIDGE DESIGN MANUAL Appendix B Loads and Loading
Spring Constants Evaluation Example
Spring Matrix
4.4-B1-4
August 1998
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Contents Page
5.0 5.1 5.1.1
5.1.2
5.2 5.2.1
5.2.2 5.3 5.3.1
5.3.2
5.3.3
5.3.4
5.3.5
Reinforced Concrete Superstructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete and Grout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Classes of Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Strength of Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Grout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Grades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Sizes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Splices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Bends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Fabrication Lengths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Percentage Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strength Design Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Design Philosophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Flexure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Shear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Strut-and-Tie Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Shear and Torsion, ACI Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Shear and Torsion, Strut-and-Tie Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Serviceability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Working Stress Design Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reinforced Concrete Box Girder Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Girder Spacing and Basic Geometries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Girder Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Basic Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Construction Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Load Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Top Slab Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Bottom Slab Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Web Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Intermediate Diaphragm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Crossbeam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Basic Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Reinforcing Steel Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . End Diaphragm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Basic Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Reinforcing Steel Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dead Load Deflection and Camber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
July 2000
5.1-1 1 1 1 1 2 3 3 3 4 4 9 9 10 10 5.2-1 1 1 1 2 2 7 7 7 7 8 5.3-1 1 1 1 3 3 4 4 7 7 11 13 13 13 14 14 16 16
5.0-i
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Contents Page
5.3.6
5.3.7 5.3.8
5.4
5.5 5.5.1
5.5.2
5.5.3 5.5.4
5.5.5 5.5.6 5.5.7 5.5.8 5.99
5.0-ii
Thermal Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Effective Bridge Temperature and Movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Differential Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hinges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Utility Openings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Confined Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Drain Holes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Access Hole and Air Vent Holes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hinges and Inverted T-Beam Pier Caps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Local Failure Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Shear Friction Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Flexural Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Hanger Tension Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Punching Shear Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Bearing Strength Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Widenings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Review of Existing Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Original Contract Plans and Special Provisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Original Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Final Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Analysis and Design Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Seismic Design Criteria for Bridge Widenings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Substructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Superstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Stability of Widening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Removing Portions of the Existing Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Attachment of Widening to Existing Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Connection Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Expansion Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Possible Future Widening for Current Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bridge Widening Falsework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Existing Bridge Widenings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17 17 17 19 19 19 19 19 5.4-1 1 4 5 6 7 8 5.5-1 1 1 1 1 2 2 2 4 5 6 7 7 7 7 11 19 20 20 21 5.99-1
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Contents
Appendix A Design Aids 5.1-A1 Reinforcing Bar Properties 5.1-A2 Bar Area vs. Bar Spacing 5.1-A3 Bar Area vs. Number of Bars 5.1-A4 Tension Development Length of Straight Deformed Bars 5.1-A5 Tension Development Length of Standard 90° and 180° Hooks 5.1-A6 Tension Lap Splice Lengths of Grade 60 Uncoated Bars 5.1-A7 Minimum Development Length and Minimum Lap Splices of Deformed Bars in Compression 5.2-A1 ρ Values for Singly Reinforced Beams fc′ = 3,000 psi fy = 60,000 psi 5.2-A2 ρ Values for Singly Reinforced Beams fc′ = 4,000 psi fy = 60,000 psi 5.2-A3 ρ Values for Singly Reinforced Beams fc′ = 5,000 psi fy = 60,000 psi 5.3-A1 Positive Moment Reinforcement 5.3-A2 Negative Moment Reinforcement 5.3-A3 Adjusted Negative Moment Case I (Design for M @ Face of Effective Support) 5.3-A4 Adjusted Negative Moment Case II (Design for M @ 1/4 Point) 5.3-A5 Load Factor Slab Design fc′ = 4,000 psi 5.3-A6 Load Factor Slab Design fc′ = 5,000 psi 5.3-A7 Slab Design — Traffic Barrier Load Appendix B Design Examples 5.2-B1 Slab Design 5.2-B2 Slab Design for Prestressed Girders 5.2-B3 Strut-and-Tie Design 5.2-B4 Working Stress Design
P65:DP/BDM5
July 2000
5.0-iii
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 5.0
Reinforced Concrete Superstructures
5.1
General
General
Prior to precast pretensioned and post-tensioned concrete members introduced in the early 1960s, all short and medium span bridges were built as cast-in-place (CIP) reinforced concrete superstructures. Examples of reinforced concrete superstructures are: flat slabs, slab and T-beams, arches, slabs for all types of steel bridges, and box girders. Many of the bridges built before 1960 are functional, durable, and structurally sound. The service life of some of these early bridges can be extended by widening their decks to accommodate increased traffic demand or to improve safety. This chapter addresses special requirements for widenings. The design aids in this chapter can also be utilized in the design of nonprestressed reinforcement in prestressed structural elements and reinforced concrete substructures.
5.1.1
Concrete and Grout A. Classes of Concrete 1.
CLASS 3000 Used in large sections with light to nominal reinforcement, mass pours, sidewalks, curbs, gutters, and nonstructural concrete guardrail anchors, luminaire bases.
2.
CLASS 4000 Used in traffic and pedestrian barriers, approach slabs, footings, box culverts, wing walls, curtain walls, retaining walls, columns, and crossbeams.
3.
CLASS 4000D Used in bridge concrete decks. Standard specifications require two coats of curing compound and a continuous wet cure for 14 days.
4.
CLASS 4000P Used for cast-in-place pile and shaft.
5.
CLASS 4000W Used underwater in seals.
6.
CLASS 5000 or Higher Used in CIP post-tensioned concrete box girder construction or in other special structural applications situations. Use of CLASS 5000 or higher requires approval of the Bridge Design Engineer, the Olympia Service Center, and Materials Lab. Place documentation in job file.
B. Strength of Concrete 1.
July 2000
The 28-day compressive design strengths (fc′) in pounds per square inch (psi) are:
5.1-1
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
General f c′
Class COMMERCIAL 3000 4000, 4000D 4000W 5000 6000 4000P
2300 3000 4000 2400* 5000** 6000 3400***
*40 percent reduction from CLASS 4000. **Concrete Class 5000 is available within a 30-mile radius of Seattle, Spokane, and Vancouver. Outside this 30-mile radius, concrete suppliers do not have the quality control rocedures and expertise to Supply Control Class 5000. ***15 percent reduction from CLASS 4000 for all drilled shafts. 2.
Relative Compressive Concrete Strength a.
During design or construction of a bridge, it is necessary to determine the strength of concrete at various stages of construction. For instance, Section 6-02.3(17)J of the Standard Specifications discusses the time at which falsework and forms can be removed to various percentages of the concrete design strength. Occasionally, construction problems will arise which require a knowledge of the relative strengths of concrete at various ages. Table 5.1-1 is intended to supply this information.
b.
Curing conditions of the concrete (especially in the first 24 hours) have a very important influence on the strength development of concrete at all ages. Temperature affects the rate at which the chemical reaction between cement and water takes place. Loss of moisture can seriously impair the concrete strength.
c.
Table 5.1-1 shows the approximate values of the minimum compressive strengths of different classes of concrete at various ages. If the concrete has been cured under continuous moist curing at an average temperature, it can be assumed that these values have been developed.
d.
If test strength is above or below that shown in Table 5.1-1, the age at which the design strength will be reached can be determined by direct proportion. For example, if the relative strength at 10 days is 64 percent instead of the minimum 70 percent shown in Table 5.1-1, the time it takes to reach the design strength can be determined as follows: Let x =
relative strength to determine the age at which the concrete will reach the design strength
x 100 = Therefore, x = 110 70 64 From Table 5.1-1, the design strength should be reached in 40 days. C. Grout Grout is usually a prepackaged cement based grout or nonshrink grout that is mixed, placed, and cured as recommended by the manufacturer. It is used under steel base plates for both bridge bearings and luminaire or sign bridge bases. Nonshrink grout is used in keyways between precast prestressed deck slabs, tri-beams, and bulb-tees. For design purposes, the strength of the grout, if properly cured, can be assumed to be equal to or greater than that of the adjacent concrete. Should the grout pad thickness exceed 4 inches, steel reinforcement shall be used.
5.1-2
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
General
The following chart shows approximate relative strength of concrete and compressive strength of different classes of concrete at various ages based on continuous moist curing at an average temperature. Relative and Compressive Strength of Concrete Table 5.1.1-1 Relative Age Strength (Days) (%) 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
5.1.2
35 43 50 55 59 63 67 70 73 75 77 79 81 83 85 87 89
Class 5000 (psi)
Class 4000 (psi)
Class 3000 (psi)
1750 2150 2500 2750 2950 3150 3350 3500 3650 3750 3850 3950 4050 4150 4250 4350 4450
1400 1720 2000 2200 2360 2520 2680 2800 2920 3000 3080 3160 3240 3320 3400 3480 3560
1050 1290 1500 1650 1770 1890 2010 2100 2190 2250 2310 2370 2430 2490 2550 2610 2670
Relative Age Strength (Days) (%) 20 21 22 23 24 25 26 27 28 30 40 50 60 70 80 90
91 93 94 95 96 97 98 99 100 102 110 115 120 125 129 131
Class 5000 (psi)
Class 4000 (psi)
Class 3000 (psi)
4550 4650 4700 4750 4800 4850 4900 4950 5000 5100 5500 5750 6000 6250 6450 6550
3640 3720 3760 3800 3840 3880 3920 3960 4000 4080 4400 4600 4800 5000 5160 5240
2730 2790 2820 2850 2880 2910 2940 2970 3000 3060 3300 3450 3600 3750 3870 3930
Reinforcement A. Grades Steel reinforcing bars are manufactured as plain or deformed bars (which have ribbed projections that grip the concrete in order to provide better bond between steel and concrete). In Washington State, main bars are always deformed. Plain bars are used for spirals and ties. Reinforcing bars conform to either the requirements of AASHTO M31, Grade 60 (ASTM A-615 Grade 60) with a 60,000 psi yield strength or in the case of bars in portions of concrete members where plastic hanging can occur during an earthquake or which are to be spliced by welding, ASTM A 706 Specifications for Low-Alloy Steel deformed Bars for Concrete Reinforcement. B. Sizes Reinforcing bars are referred to in the contract plans and specifications by number and vary in size from #3 to #18. For bars up to and including #8, the number of the bar coincides with the bar diameter in eighths of an inch. The #9, #10, and #11 bars have diameters that provide areas equal to 1″ x 1″ square bars, 11/8″ x 11/8″ square bars and 11/4″ x 11/4″ square bars respectively. Similarly, the #14 and #18 bars correspond to 11/2″ x 11/2″ and 2″ x 2″ square bars, respectively. Tables 5.1-A1 through 5.1-A3 in Appendix A, show the sizes, number, and various properties of the types of bars used in Washington State.
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5.1-3
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
General
C. Development 1.
Development Length, ld, in Tension Development length or anchorage of reinforcement is required on both sides of a point of maximum stress at any section of a reinforced concrete member. Development of bars in tension involves calculating the basic development length, ldb, which is modified by factors to reflect bar spacing, cover, enclosing transverse reinforcement, top bar effect, type of aggregate, epoxy coating, and ratio of required area to provided area of reinforcement to be developed. The development length, ld (including all applicable modification factors) must not be less than 12 inches. Tables 5.1-A4 and 5.1-A5 in Appendix A, show the tension development length for both uncoated and epoxy coated Grade 60 bars for normal weight concrete with specified strengths of 3,000 to 6,000 psi.
2.
Development Length, ld, in Compression The basic development lengths for deformed bars in compression are shown in Table 5.1-A7, Appendix A. These values may be modified for ratio of required area vs. provided area of reinforcement, or for bars enclosed in a 1/4 inch diameter spiral at 4 inch maximum pitch. However, the minimum development length is 1 foot 0 inches (office practice).
3.
Standard End Hook Development Length, ldh, in Tension Standard end hooks, utilizing 90 and 180 degree end hooks, are used to develop bars in tension where space limitations restrict the use of straight bars. End hooks on compression bars are not effective for development length purposes. Figures 5.1.2-1 and 5.1.2-2 and Table 5.1.2-1 show the minimum embedment lengths necessary to provide 2 inches of cover on the tails of 90 and 180 degree end hooks. Epoxy coating does not affect the tension development lengths, ldh, of standard 90 and 180 degree end hooks. The values shown in Table 5.1-1A5, Appendix A, show the tension development lengths for normal weight concrete with specified strengths of 3,000 to 6,000 psi.
D. Splices Three methods are used to splice reinforcing bars; lap splices, mechanical splices, and welded splices. Lap splicing of reinforcing bars is the most common method. The Contract Plans should clearly show the locations and lengths of lap splice. Lap splices are not permitted for bars larger than #11. No lap splices, for either tension or compression bars, shall be less than 2 feet 0 inches (office practice). See Section 8.32 of the Standard Specifications for Highway Bridges and Section 6-02.3(24)D Standard Specifications for additional splice requirements. 1.
Lap Splices — Tension Many of the same factors which affect development length affect splices. Consequently, tension lap splices are a function of the bar’s development length, ld. There are three classes of tension lap splices: Class A, B, and C. Designers are encouraged to splice bars at points of minimum stress and to stagger lap splices along the length of the bars.
5.1-4
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
General
Minimum Embedment Lengths to Provide 2-inch Cover to Tail of Standard 180° End Hooks Table 5.1.2-1 #3
#4
#5
#6
#7
#8
#9
#10
#11
#14
#18
6″
7″
9″
10″
1′-0″
1′-2″
1′-3″
1′-5″
1′-7″
2′-10″
3′-7″
Standard 180° and 90° End Hooks Figure 5.1.2-1
Special Confinement for 180° and 90° End Hooks Figure 5.1.2-2
July 2000
5.1-5
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
General Recommended End Hooks Table 5.1.2-2
5.1-6
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
General
Figure 5.1.2-3
July 2000
5.1-7
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
General
(a)
(b)
(c)
Figure 5.1.2-4
5.1-8
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
General
Table 5.1A6 in Appendix A, shows tension lap splices for both uncoated and epoxy coated Grade 60 bars for normal weight concrete with specified strengths of 3,000 to 6,000 psi. For additional requirements, see Section 8.32.3 of the AASHTO Standard Specifications for Highway Bridges. For Seismic Performance Categories C and D, Section 8.4.1(F) of the AASHTO Standard Specifications for Seismic Design of Highway Bridges, the lap splices for longitudinal column bars are permitted only within the center half of the column height and shall not be less than the lap splices given in Table 5.1-A6 in Appendix A, or 60 bar diameters whichever is greater. Note that the maximum spacing of the transverse reinforcement (i.e., column ties) over the length of the splice shall not exceed the smaller of 4 inches or 1/4 of the minimum column plan dimension. 2.
Lap Splices — Compression The compression lap splices shown in Table 5.1-A7 (right-hand column) in Appendix A, are for concrete strengths greater than 3,000 psi. If the concrete strength is less than 3,000 psi, the compression lap splices should be increased by one third. Note that when two bars of different diameters are lap spliced, the length of the lap splice shall be the larger of the lap splice for the smaller bar or the development length of the larger bar.
3.
Mechanical Splices A second method of splicing is by mechanical splices, which are proprietary splicing mechanisms. The requirements for mechanical splices are found in Section 6-02.3(24)F of the Standard Specifications, Sections 8.32.2 and 8.32.3 of the AASHTO Standard Specifications for Highway Bridges, and Section 8.4.1(F) of the Standard Specifications for Seismic Design of Highway Bridges.
4.
Welded Splices Welding of reinforcing bars is the third acceptable method of splicing reinforcing bars. Section 6-02.3(24)E of the Standard Specifications describes the requirements for welding reinforcing steel. On modifications to existing structures, welding of reinforcing bars may not be possible because of the non-weldability of some steels. See Sections 8.32.2 and 8.32.3 of the AASHTO Standard Specifications for Highway Bridges and Section 8.4.1(F) of the Standard Specifications for Seismic Design of Highway Bridges for additional welded splice requirements.
E. Bends For standard hooks and bend radii, see Table 5.1-15. Note that the tail lengths are greater for the 135° seismic tie hook than for the regular or nonseismic 135° tie hook. For field bending requirements, see Section 6-02.3(24)A of the Standard Specifications. F. Fabrication Lengths Reinforcing bars are normally stocked in lengths of 60 feet. They can also be fabricated in longer lengths.
July 2000
5.1-9
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
General
The maximum overall bar lengths to be specified on the plans are: Bar Size #3 #4, #5 #6, #7 #8, #9, #10 #11, #14, #18
Maximum Length 30′-0″ 40′-0″ 60′-0″ 60′-0″ 60′-0″
Where possible, specify lengths 60 feet and less for bar sizes #8 through #18. Because of placement considerations, the overall lengths of bar size #3 has been limited to 30 feet and bar sizes #4 and #5 to 40 feet. To use longer lengths, the designer should make sure that the bars can be placed and transported by truck. See Table 5.1-A1 in Appendix A. G. Placement Placement of reinforcing bars can be a problem during construction. Reinforcing bars are more than just lines on the drawing, they have size, weight, and volume. In confined areas, the designer should ensure that reinforcing bars can be placed. Sometimes it may be necessary to make a large scale drawing of reinforcement to look for interference and placement problems. If interference is expected, additional details may be required in the contract plans showing how to handle the interference and placement problems. H. Percentage Requirements There are several AASHTO requirements to ensure that minimum reinforcement is provided in reinforced concrete members. 1.
Flexure The reinforcement provided at any section should be adequate to develop a moment at least 1.2 times the cracking moment calculated on the basis of the modulus of rupture for normal weight concrete. The modulus of rupture for normal weight concrete is 7.5 √fc′ . This requirement may be waived if the area of reinforcement provided is at least one-third greater than that required by analysis. For additional minimum reinforcement required, see Section 8.17, AASHTO Standard Specifications for Highway Bridges.
2.
Compression For columns, the area of longitudinal reinforcement shall not exceed 0.08 nor be less than 0.01 of the gross area, Ag, of the section. Preferably, the ratio of longitudinal reinforcement should not exceed 0.04 of the gross area, Ag, to ensure constructibility and placement of concrete. If a ratio greater than 0.04 is used, the designer should verify that concrete can be placed. If for architectural purposes the cross section is larger than that required by the loading, a reduced effective area may be used. The reduced effective area shall not be less than that which would require 1percent of the longitudinal area to carry the loading. Additional lateral reinforcement requirements are given in Section 8.18, AASHTO Standard Specifications for Highway Bridges, and for plastic hinge zones, see Section 8.4.1(D), AASHTO Standard Specifications for the Seismic Design of Highway Bridges. For column reinforcing, ASTM A 706 reinforcing should be pecified to improve durability.
3.
Other Minimum Reinforcement Requirements For minimum shear reinforcement requirements, see Section 8.19 and for minimum temperature and shrinkage reinforcement, see Section 8.20, AASHTO Standard Specifications for Highway Bridges.
5.1-10
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 5.2
Design Methods
5.2.1
Strength Design Method
Design Methods
A. Design Philosophy In the strength design method or ultimate strength method, the service loads are increased by load factors to obtain the ultimate design load. The structural members are then proportioned to provide the design ultimate strength. Several textbooks listed in the bibliography, which are excellent sources [1,2,3]. B. Flexure The basic strength design requirement can be expressed as follows: Design Strength ≥ Required Strength or φ Mn ≥ Mu
(1)
For design purposes, the area of reinforcement for a singly reinforced beam or slab can be determined by letting: Mu = φ Mn = φ [As (fy) (d – a/2)]
(2)
However, if a As(fy)/(0.85)(fc′)(b) and ρ = As/(b)(d)
(3)
Equation (2) can be expressed as: Mu/φ (b) (d)2 = ρ (fy) [1 – 0.59 (ρ) fy/fc′]
(4)
Tables 5.2-1 through 5.2-3 in Appendix 5.2-A1, -A2, and -A3, were prepared based on Eq (4) to quickly determine the amount of reinforcing steel required, As required, when Mu, fc′, fy, b, and d are known. An alternate approach is to solve directly for As required from: As required =
0.85 fc′ (b) fy
( √ d –
d2 –
31.3725 Mu fc′ (b)
)
where
Mu = kips – in fc′ = ksi
(5)
Similarly, substituting 1.2Mcr for Mu, As min can be found from: As min =
0.85 fc′ (b) fy
( √ d –
d2 –
0.124 h2 √ f c′
)
where
h = slab thickness
(6)
From AASHTO 8.16.3.1.1 and 8.16.3.2.2, As max can be found from: As max = 0.6375 β1 (b) (d) where
fc ′ fy
(
87 87 + fy
)
(7)
β1 = 0.85 if fc′ ≤ 4 ksi and β1 = 0.85 – 0.05 (fc′ – 4) if fc′ > 4 ksi, but not less than 0.65
Tension reinforcement should be designed in the following order:
July 2000
1.
From Eq (5) or Tables 5.2-A1 through 5.2-A3 in Appendix A, determine As required.
2.
From Eq (6) determine As min.
3.
From Eq (7) or Tables 5.2-A1 through 5.2-A3 in Appendix A, determine As max.
5.2-1
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 4.
Design Methods
If As required > As max, increase the member’s dimensions. If As max > As required > As min, use As ≥ As required. If As required < As min < 1.33 As required, use As ≥ As min. If 1.33 As required < As min, use As ≥ 1.33 As required. Always use As ≤ As max.
See Appendix 5.2-B1 and 5.2-B2 for design examples. C. Shear The AASHTO Standard Specifications for Highway Bridges addresses shear design of members in Section 8.16.6. Shear friction provisions (Section 8.16.6.4) are applied to transfer shear across a plane, such as: an existing or potential crack, an interface between dissimilar materials, or at a construction joint between two sections of concrete placed at different times. The shear design for deep beams is not addressed in the AASHTO Standard Specifications, but is discussed in Section 11.8, ACI 318-89 Building Code Requirements for Reinforced Concrete and Commentary, and ACI-ASCE Committee 343 Analysis and Design of Reinforced Concrete Bridge Structures [4,5,6]. D. Strut-and-Tie Model 1.
General Strut-and-tie models may be used to determine internal force effects near supports and the points of application of concentrated loads [16]. The strut-and-tie model should be considered for the design of deep footings and pile caps or other situations in which the distance between the centers of applied load and supporting reaction is less than twice the member thickness.
2.
Structural Modeling The structure and a component or region, thereof, may be modeled as an assembly of steel tension ties and concrete compressive struts interconnected at nodes to form a truss capable of carrying all the applied loads to the supports as shown in Figure 5.2.1-1 for a deep beam. The required widths of compression struts and tension ties shall be considered in determining the geometry of the truss. The truss model does not necessarily need to conform to structural stability as a real truss would. The factored resistance, Pn,of struts and ties shall be taken as that of axially loaded components. Pu′ = ϕ Pn where: Pn = nominal resistance of strut or tie (KIP) ϕ = 0.7 Compression ϕ = 0.9 Tension
5.2-2
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 3.
Design Methods
Proportioning of Compressive Struts a.
Strength of Unreinforced Strut The nominal resistance of an unreinforced compressive strut shall be taken as: Pn = fcuAcs where: Pn = nominal resistance of a compressive strut (kips) fcu = limiting compressive stress (ksi) Acs = effective cross-sectional area of strut (in2)
b.
Effective Cross-Sectional Area of Strut The value of Acs shall be determined by considering both the available concrete area and the anchorage conditions at the ends of the strut, as shown in Figure 5.2.1-2. When a strut is anchored by reinforcement, the effective concrete area may be considered to extend a distance of up to six bar diameters from the anchored bar, as shown in Figures 5.2.1-2(a), 5.2.1-2(b), and 5.2.1-2(c).
c.
Limiting Compressive Stress in Strut The limiting compressive stress, fcu, shall be taken as: fcu =
fc ′ 0.8 + 170ε1
≤ 0.8 fc′
for which: ε1 = εs + (εs + 0.002) cot2 αs where: as
= the smallest angle between the compressive strut and adjoining tension ties (DEG) εs = the tensile strain in the concrete in the direction of the tension tie (in/in) fc′ = specified compressive strength (ksi) d.
Reinforced Strut If the compressive strut contains reinforcement that is parallel to the strut and detailed to develop its yield stress in compression as shown in Figure 5.2.1-2(d), the nominal resistance of the strut shall be taken as: Pn = fcu Acs + fy Ass where: Ass = area of reinforcement in the strut (in2)
July 2000
5.2-3
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Design Methods
Strut-and-Tie Model for Deep Beam Figure 5.2.1-1
5.2-4
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Design Methods
Influence of Anchorage Conditions on Effective Cross-Sectional Area of Strut Figure 5.2.1-2
July 2000
5.2-5
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 4.
Design Methods
Proportioning of Tension Ties a.
Strength of Tie Tension tie reinforcement shall be anchored to the nodal zones by specified embedment lengths, hooks, or mechanical anchorages. The tension force shall be developed at the inner face of the nodal zone. The nominal resistance of a tension tie in KIP shall be taken as: Pn = fy Ast + Aps [fpe + fy] where: Ast Aps fy fpe
b.
= = = =
total area of longitudinal mild steel reinforcement in the tie (IN2) area of prestressing steel (IN2) yield strength of mild steel longitudinal reinforcement (KSI) stress in prestressing steel due to prestress after losses (KSI)
Anchorage of Tie The tension tie reinforcement shall be anchored to transfer the tension force therein to the node regions of the truss in accordance with the requirements for development of reinforcement as specified in Article 5.1.2C.
5.
Proportioning of Node Regions Unless confining reinforcement is provided and its effect is supported by analysis or experimentation, the concrete compressive stress in the node regions of the strut shall not exceed: • For node regions bounded by compressive struts and bearing areas: 0.85 ϕ fc′ • For node regions anchoring a one-direction tension tie: 0.75 ϕ fc′ • For node regions anchoring tension ties in more than one direction: 0.65 ϕ fc′ where: ϕ = 0.7 resistance factor for bearing on concrete The tension tie reinforcement shall be uniformly distributed over an effective area of concrete at least equal to the tension tie force divided by the stress limits specified herein. In addition to satisfying strength criteria for compression struts and tension ties, the node regions shall be designed to comply with the stress and anchorage limits.
6.
Crack Control Reinforcement Structures and components or regions thereof, except for slabs and footings, which have been designed in accordance with the provisions strut-and-tie model, shall contain an orthogonal grid of reinforcing bars near each face. The spacing of the bars in these grids shall not exceed 12.0 inches. The ratio of reinforcement area to gross concrete area shall not be less than 0.003 in each direction. Crack control reinforcement, located within the tension tie, may be considered as part of the tension tie reinforcement.
5.2-6
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Design Methods
E. Shear and Torsion, ACI Method The AASHTO Standard Specifications for Highway Bridges does not address the design of reinforced concrete members for torsion. The design for shear and torsion is based on ACI 318-95 Building Code Requirements for Structural Concrete and Commentary (318F-95) and is satisfactory for bridge members with dimensions similar to those normally used in buildings. The AASHTO LRFD Specifications Article 5.8.3.6 may also be used for design of sections subjected to shear and torsion. F. Shear and Torsion, Strut-and-Tie Method According to Hsu [7], utilizing ACI 318-89 for members is awkward and overly conservative when applied to large-size hollow members. Collins and Mitchell [8] propose a rational design method for shear and torsion based on the compression field theory or strut and tie method for both prestressed and non-prestressed concrete beams. These methods assume that diagonal compressive stresses can be transmitted through cracked concrete. In addition to transmitting these diagonal compressive stresses, shear stresses are transmitted from one face of the crack to the other by a combination of aggregate interlock and dowel action of the stirrups. For recommendations and design examples for beams in shear and torsion, the designer can refer to the paper by M.P. Collins and D. Mitchell, Shear and Torsion Design of Prestressed and Non-Prestressed Concrete Beams, PCI Journal, September-October 1980, pp. 32-100 [8]. See Appendix 5.2-B3 for a strut and tie design example for a pier cap. G. Deflection Flexural members are designed to have adequate stiffness to limit deflections or any deformations which may adversely affect the strength or serviceability of the structure at service load plus impact. The minimum superstructure depths are specified in AASHTO Table 8.9.2 and deflections shall be computed in accordance with Section 8.13, AASHTO Standard Specifications for Highway Bridges. H. Seviceability In addition to the deflection control requirements described above, service load stresses shall be limited to satisfy fatigue (Section 8.16.8.3) and for distribution of tension reinforcement when fy for tension reinforcement exceeds 40,000 psi (Section 8.16.8.4 AASHTO Specifications). To control cracking of the concrete, tension reinforcement at maximum positive and negative moment sections shall be chosen so that the calculated service load stress, fs in ksi, shall be less than the value computed by: z 1/ fs = 3 ≤ 0.6 fy (dc x A) The requirements for control of cracking apply to superstructure elements only The calculated service load stress is calculated utilizing Working Stress Design (WSD) principles described below. The values of dc and A are defined in Section 8.16.8.4 of the AASHTO Standard Specifications for Highway Bridges. The value z shall be 130 kips per inch for girder and crossbeam reinforcing bars in negative moment regions, and all deck reinforcing bars. A value of 170 kips per inch shall be used for all other positive moment regions. Note that this check is for distribution of flexural reinforcement to control cracking. See Appendix 5.2-B2 which shows the flexural reinforcement at a pier location placed equally in top and bottom layers. When this is done, the total slab thickness can be used in computing A.
July 2000
5.2-7
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 5.2.2
Design Methods
Working Stress Design Method Prior to the strength design method, introduced in the 1973, AASHTO Standard Specifications for Highway Bridges, the working stress design (WSD) method was used to design bridges. Many design aids were produced as a result. The ACI Publication SP-3, Reinforced Concrete Design Handbook Working Stress Method [9], is a publication that was widely used by designers and several textbooks have sections devoted to WSD [1,2]. Working Stress Design principles are used to compute the tensile stress, fs, and Mcr, which are used to check crack control and minimum flexural reinforcement respectively. Design aid for working stress design method for Class 3000 and 4000 concrete is provided in Appendix B4.
P65:DP/BDM5
5.2-8
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 5.3
Reinforced Concrete Box Girder Bridges
Reinforced Concrete Box Girder Bridges A typical box girder bridge is comprised of top and bottom concrete slabs connected by a series of vertical girder stems. This section is a guide for designing: Top slab Bottom slab Girder stem (web) For design criteria not covered, see Section 2.4.1.C.
5.3.1
Girder Spacing and Basic Geometries A. Girder Spacing The most economical web spacing for ordinary box girder bridges varies from about 8 to 12 feet. Greater girder spacing requires some increase in both top and bottom slab thickness, but the cost of the additional concrete can be offset by decreasing the total number of girder stems. Fewer girder stems reduces the amount of form work required and a lower cost. The number of girder stems can be reduced by cantilevering the top slab beyond the exterior girders. A deck overhang of approximately one-half the girder spacing generally gives satisfactory results. This procedure usually results in a more aesthetic as well as a more economical bridge. For girder stem spacing in excess of 12 feet or cantilever overhang in excess of 6 feet, transverse post-tensioning shall be used. B. Basic Dimensions (Figure 5.3.1-1) 1.
Top Slab Thickness, T1 (includes 1/2″ wearing surface) T1 = 12 x (S+10)/30 but not less than 7″ with overlay or 7.5″ without overlay.
2.
Bottom Slab Thickness, T2 a.
Near Center Span T2 = 12 x (Sclr)/16 but not less than 5.5″ (normally 6.0″ is used).
b.
Near Intermediate Piers Thickening of the bottom slab is often used in negative moment regions to control compressive stresses that are significant. Transition slope = 24:1 (see T2′ in Figure 5.3.2-8).
3.
Girder Stem (Web) Thickness, T3 a.
Near Center Span Minimum T3 = 9.0″ — vertical Minimum T3 = 10.0″ — if sloped
b.
Near Supports Thickening of girder stems is used in areas adjacent to supports to control shear requirements.
July 2000
5.3-1
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
Changes in girder web thickness shall be tapered for a minimum distance of 12 times the difference in web thickness. Maximum T3 = T3+4.0″ maximum Transition length = 12 x (T3) in inches
Basic Dimensions Figure 5.3.1-1
5.3-2
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 4.
Reinforced Concrete Box Girder Bridges
Intermediate Diaphragm Thickness, T4 and Diaphragm Spacing a.
For tangent and curved bridge with R > 800 feet T4 = 0″ (Diaphragms are not required.)
b.
For curved bridge with R < 800 feet T4 = 8.0″ Diaphragm spacing shall be as follows: For 600′ < R < 800′at 1/2 pt. of span. For 400′ < R < 600′ at 1/3 pt. of span. For R < 400′ at 1/4 pt. of span.
C. Construction Considerations Review the following construction considerations to ensure that: 1.
Construction joints at slab/stem interface or fillet/stem interface at top slab are appropriate.
2.
All construction joints to have roughened surfaces.
3.
Bottom slab is parallel to top slab (constant depth).
4.
Girder stems are vertical.
5.
Dead load deflection and camber to nearest 1/8″.
6.
Skew and curvature effects have been considered.
7.
Thermal effects have been considered.
8.
The potential for falsework settlement is acceptable. This always requires added stirrup reinforcement in sloped outer webs.
D. Load Distribution 1.
Unit Design According to the AASHTO specifications, the entire slab width shall be assumed effective for compression. It is both economical and desirable to design the entire superstructure as a unit rather than as individual girders. When a reinforced box girder bridge is designed as an individual girder with a deck overhang, the positive reinforcement is congested in the exterior cells. The unit design method permits distributing all girder reinforcement uniformly throughout the width of the structure.
2.
July 2000
Dead Loads a.
Box dead loads.
b.
D.L. of top deck forms — 5 lbs. per sq. ft. of the area. — 10 lbs. per sq. ft. if web spacing > 10′−0″.
c.
Traffic barrier.
d.
Overlay, intermediate diaphragm, and utility weight if applicable.
5.3-3
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 3.
Reinforced Concrete Box Girder Bridges
Live Load a.
Superstructure No. of lanes = slab width (curb to curb) / 14 Fractional lane width will be used For example, 58 roadway / 14 = 4.14, then no. of lanes = 4.14
b.
Substructure No. of lanes = slab width (curb to curb) / 12 Fractional lane width will be ignored For example, 58 roadway / 12 = 4.83, then no. of lanes = 4.0
c.
5.3.2
Overload if applicable.
Reinforcement This section discusses moment reinforcement for top slab, bottom slab, and intermediate diaphragms in box girders. A. Top Slab Reinforcement 1.
Near Center of Span Figure 5.3.2-1 shows the reinforcement required near the center of the span and Figure 5.3.2-2 shows the overhang reinforcement.
2.
a.
Transverse reinforcing in the top and bottom layers to transfer the load to the main girder stems shall be equal in size and spacing.
b.
Bottom longitudinal “distribution reinforcement” in the middle half of the deck span (Seff) to aid in distributing the wheel loads.
c.
Top longitudinal “temperature and shrinkage reinforcement.”
Near Intermediate Piers Figure 5.3.2-3 illustrates the reinforcement requirement near intermediate piers. See Appendix 5.2-B2 for design of longitudinal deck reinforcement. a.
Transverse reinforcing same as center of span.
b.
Longitudinal reinforcement to resist negative moment (see Figure 5.3.2-3).
c.
“Distribution of flexure reinforcement” to limit cracking (see Figure 5.3.2-3). Allowable fs = z/(dc x A)
3.
1/ 3
≤ 0.6fy, where z = 130 kips per inch.
Bar Patterns a.
Transverse Reinforcement It is preferable to place the transverse reinforcement parallel to the X-Beam and end diaphragm on skews up to 25 degrees or less. Where skew angles exceed 25 degrees, the transverse bars are normal to bridge center line and the areas near the expansion joint and bridge ends are reinforcement by partial length bars. The bottom transverse slab reinforcement is discontinued at the X-Beam (see Figure 5.3.2-4).
5.3-4
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures b.
Reinforced Concrete Box Girder Bridges
Longitudinal Reinforcement For longitudinal reinforcing bar patterns, see Chapter 6.
Partial Section Near Center of Span Figure 5.3.2-1
Overhang Detail Figure 5.3.2-2
July 2000
5.3-5
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
Top Slab Flexural Reinforcing Near Intermediate Pier Figure 5.3.2-3
Partial Plans at Abutments Figure 5.3.2-4
5.3-6
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
B. Bottom Slab Reinforcement 1.
Near Center of Span Figure 5.3.2-5 shows the reinforcement required near the center of the span. a.
Minimum transverse “distributed reinforcement.” As=0.005 x flange area with 1/2 As distributed equally to each surface.
b.
Longitudinal “main reinforcement” to resist positive moment.
c.
Check “distribution of flexure reinforcement” to limit cracking (see Figure 5.3.2-5). Allowable fs = z/(dc x A)
d. 2.
1/ 3
≤ 0.6fy, where z = 170 kips per inch.
Add steel for construction load (sloped outer webs).
Near Intermediate Piers Figure 5.3.2-6 shows the reinforcement required near intermediate piers. a.
Minimum transverse reinforcement same as center of span.
b.
Minimum longitudinal “temperature and shrinkage reinforcement.” As=0.004 x flange area with 1/2 As distributed equally to each face.
c. 3.
Add steel for construction load (sloped outer webs).
Bar Patterns a.
Transverse Reinforcement See top slab bar patterns, Figures 5.3.2-1, 5.3.2-2, and 5.3.2-3. All bottom slab transverse bars shall be bent at the outside face of the exterior web. For vertical web, the tail will be 1′-0″ and for sloping exterior web 2′-0″ minimum splice with the outside web stirrups. See Figure 5.3.2-7.
b.
Longitudinal Reinforcement For longitudinal reinforcing bar patterns, see Chapter 6.
C. Web Reinforcement 1.
Vertical Stirrups (see Figure 5.3.2-8) The web reinforcement should be designed for the following requirements: Vertical shear requirements. Out of plane bending on outside web due to live load on cantilever overhang. Horizontal shear requirements for composite flexural members. A b Minimum v = 50 w (#5 bars @ 1′-6″), where bw = no. of girder stems (T3). s fy
July 2000
5.3-7
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 2.
Reinforced Concrete Box Girder Bridges
Web Longitudinal Reinforcement (see Figure 5.3.2-8) If the depth of the side face of a member exceeds 3 feet, longitudinal skin reinforcement shall be uniformly distributed along both side faces of the member for a distance d/2 nearest the flexural tension reinforcement. The area of skin reinforcement Ask per foot of height on each side face shall be ≥ 0.012 (d – 30). The maximum spacing of skin reinforcement shall not exceed the lesser of d/6 and 12 inches. Such freinforcement may be included in strength computations if a strain compatibility analysis is made to determine stresses in the individual bars or wires. The total area of longitudinal skin reinforcement in both faces need not exceed one half of the flexural tensile reinforcement. Where As = Total required area of longitudinal reinforcing steel. Reinforcing steel spacing < Web Thickness (T3) or 12″. For cast-in-place sloped outer webs, increase inside stirrup reinforcement and bottom slab top transverse reinforcement as required for the web moment locked-in during construction of the top slab. This moment about the bottom corner of the web is due to tributary load from the top slab concrete placement plus 10 psf form dead load. See Figure 5.3.2-10 for typical top slab forming.
Bottom Slab Reinforcement Near Center of Span Figure 5.3.2-5
Bottom Slab Reinforcement Near Intermediate Pier Figure 5.3.2-6
5.3-8
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
Figure 5.3.2-7
July 2000
5.3-9
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
Figure 5.3.2-8
5.3-10
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
D. Intermediate Diaphragm (see Figure 5.3.2-9)
Figure 5.3.2-9 Intermediate diaphragms are not required for bridges on tangent alignment or curved bridges with an inside radius of 800 feet or greater. Notes: 1.
If the bar is not spliced, the horizontal dimension should be 4″ shorter than the slab width.
2.
Stirrup hanger must be placed above longitudinal steel when diaphragm is skewed and slab reinforcement is placed normal to center of roadway. (Caution: Watch for the clearance with longitudinal steel).
3.
The reinforcement should have at least one splice to facilitate proper bar placement.
Notes:
July 2000
5.3-11
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
1.
The diagonal brace supports web forms during web pour. After cure, the web is stiffer than the brace, and the web attracts load from subsequent concrete placements.
2.
The tributary load includes half the overhang because the outer web form remains tied to and transfers load to the web which is considerably stiffer than the formwork. Increase Web Reinf. for Locked-In Construction Load
Due to Typical Top Slab Forming for Sloped Web Box Girder Figure 5.3.2-10
5.3-12
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 5.3.3
Reinforced Concrete Box Girder Bridges
Crossbeam A. Basic Geometry For aesthetic purposes, it is preferable to keep the crossbeam within the superstructure so that the bottom slab of the entire bridge is a continuous plane surface interrupted only by the columns. Although the depth of the crossbeam may be limited, the width can be made as wide as necessary to satisfy design requirements. Normally, it varies from 3 feet to the depth of box but is not less than column sizes to utilize the column reinforcement (see Figure 5.3.3-1 and 5.3.3-2). Crossbeams on box girder type of construction shall be designed as a T beam utilizing the flange in compression, assuming the deck slab acts as a flange for positive moment and bottom slab a flange for negative moment. The effective overhang of the flange on a cantilever beam shall be limited to six times the flange thickness. The bottom slab thickness is frequently increased near the crossbeam in order to keep the main box girder compressive stresses to a desirable level for negative girder moments (see Figure 5.3.2-8). This bottom slab flare also helps resist negative crossbeam moments. Consideration should be given to flaring the bottom slab at the crossbeam for designing the cap even if it is not required for resisting main girder moments. B. Reinforcing Steel Details Special attention should be given to the details to ensure that the column and crossbeam reinforcement will not interfere with each other. This can be a problem especially when round columns with a great number of vertical bars must be meshed with a considerable amount of positive crossbeam reinforcement passing over the columns. 1.
Top Reinforcement Provide negative moment reinforcement at the 1/4 point of the square or equivalent square columns (see Appendix 5.3-A1 and 5.3-A4). a.
When Skew Angle < 10 Degrees If the bridge is tangent or slightly skewed and the deck reinforcement is parallel to the cross beam, the negative cap reinforcement can be placed either in contact with top deck negative reinforcement or directly under the main deck reinforcement (see Figure 5.3.3-1). Reinforcement must be epoxy coated if the location of reinforcement is less than 4″ below top of deck.
b.
When Skewed Angle > 10 Degrees When the structure is on a greater skew and the deck steel is normal or radial to the longitudinal centerline of the bridge, the negative cap reinforcement should be lowered to below the main deck reinforcement (see Figure 5.3.3-2).
c.
To avoid cracking of concrete, interim reinforcements are required below the construction joint in diaphgragms and crossbeams. The interim reinforcements shall develop a moment capacity of 1.2 Mcr where Mcr may be given as:
July 2000
5.3-13
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures Mcr =
Reinforced Concrete Box Girder Bridges
fr Ig yt
fr = 7.5 √ fc′ Mcr = 1.25 bh2
√ f c′
Mn = 1.2Mcr = 1.5 bh2 √ fc′ As =
5.3.4
0.85 fc′ b fy
( √ d –
d2 –
31.3725M fc ′
)
End Diaphragm A. Basic Geometry Bearings at the end diaphragms are usually located under the girder stems and transfer loads directly to the pier (see Figure 5.3.3-3). In this case, the diaphragm width should be equal to or greater than bearing sole plate grout pads (see Figure 5.3.3-4). Designer should provide access space for maintenance and inspection of bearings. Allowance should be provided to remove and replace the bearings. Lift point locations, jack capacity, number of jacks, and maximum permitted lift should be shown in the plan details.
Skew Angle ≤ 10° Crossbeam Top Reinforcement Figure 5.3.3-1
5.3-14
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
Skew Angle > 10° Crossbeam Top Reinforcement Figure 5.3.3-2
Bearing Locations, Lift Points, Jack Capacity, and Maximum Lift Permitted at End Diaphragm Figure 5.3.3-3
July 2000
5.3-15
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
“L” Abutment End Diaphragm Figure 5.3.4-1 The end diaphragms should be wide enough to provide adequate reinforcing embedment length. When the structure is on a skew greater than 10 degrees and the deck steel is normal or radial to the center of the bridge, the width should be enough to accommodate the embedment length of the reinforcement. The most commonly used type of end diaphragm is shown in Figure 5.3.3-5. The dimensions shown here are used as a guideline and should be modified if necessary. This end diaphragm is used with a stub abutment and overhangs the stub abutment. It is used on bridges with an overall or out-to-out length less than 400 feet. If the overall length exceeds 400 feet, an “L” abutment should be used. B. Reinforcing Steel Details Typical reinforcement details for an end diaphragm are shown in Figure 5.3.3-6.
5.3.5
Dead Load Deflection and Camber Camber is the adjustment made to the vertical alignment to compensate for the anticipated dead load deflection and the long-term deflection caused by shrinkage and creep. The multipliers for estimating long-term deflection and camber for reinforced concrete flexural members may be taken as shown in Table 1.
5.3-16
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
Multipliers for Estimating Long-term Deflection and Camber of Concrete Members Table 5.3.5-1 Multiplier Coefficient Girder Adjacent to Existing/Stage Construction Deflection (downward) — apply to the elastic deflection due to the weight of member
1.90
Deflection (downward) — apply to the elastic deflection due to superimposed dead load only
2.20
Girder Away From Existing/Stage Construction Deflection (downward) — apply to the elastic deflection due to the weight of member
2.70
Deflection (downward) — apply to the elastic deflection due to superimposed dead load only
3.00
In addition to dead load deflection, forms and falsework tend to settle and compress under the weight of freshly placed concrete. The amount of this takeup is dependent upon the type and design of the falsework, workmanship, type and quality of materials and support conditions. The camber should be modified to account for anticipated takeup in the falsework.
5.3.6
Thermal Effects Concrete box girder bridges are subjected to stresses and/or movements resulting from temperature variation. Temperature effects result from time-dependent variations in the effective bridge temperature and from temperature differentials within the bridge superstructure. A. Effective Bridge Temperature and Movement Fluctuation in effective bridge temperature causes expansion and contraction of the structure. Proper temperature expansion provisions are essential in order to ensure that the structure will not be damaged by thermal movements. These movements, in turn, induce stresses in supporting elements such as columns or piers, and result in horizontal movement of the expansion joints and bearings. For more details, see Chapter 8. B. Differential Temperature Although time-dependent variations in the effective temperature have caused problems in both reinforced and prestressed concrete bridges, detrimental effects caused by temperature differential within the superstructure have occurred only in prestressed bridges. Therefore, computation of stresses and movements resulting from the vertical temperature gradients is not included in this chapter. For more details, see AASHTO Guide Specifications, Thermal Effects on Concrete Bridge Superstructures (1989).
July 2000
5.3-17
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
End Diaphragm With Stub Abutment Figure 5.3.4-2
Typical End Diaphragm Reinforcement Figure 5.3.4-3
5.3-18
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 5.3.7
Reinforced Concrete Box Girder Bridges
Hinges Hinges are one of the weakest links of box girder bridges subject to earthquake forces and it is desirable to eliminate hinges or reduce the number of hinges. For more details on the design of hinges, see Section 5.4. Designer should provide access space or pockets for maintenance and inspection of bearings. Allowance should be provided to remove and replace the bearings. Lift point locations, maximum lift permitted, jack capacity, and number of jacks should be shown in the hinge plan details.
5.3.8
Utility Openings A. Confined Spaces A confined space is any place having a limited means of exit which is subject to the accumulation of toxic or flammable contaminants or an oxygen deficient environment. Confined spaces include but are not limited to pontoons, box girder bridges, storage tanks, ventilation or exhaust ducts, utility vaults, tunnels, pipelines, and open-topped spaces more than 4 feet in depth such as pits, tubes, vaults, and vessels. The designer should provide for the following: • A sign with “Confined Space Authorized Personnel Only.” • In the “Special Provisions Check List,” alert and/or indicate that a special provision might be needed to cover confined spaces. B. Drain Holes Drain holes should be placed in the bottom slab at the low point of each cell to drain curing water during construction and any rain water that leaks through the deck slab. Additional drains shall be provided as a safeguard against water accumulation in the cell (especially when waterlines are carried by the bridge). In some instances, drainage through the bottom slab is difficult and other means shall be provided (i.e., cells over large piers and where a sloping exterior web intersects a vertical web). In this case, a horizontal drain should be provided through the vertical web. Figure 5.3.8-1 shows drainage details for the bottom slab of concrete box girder bridges. C. Access Hole and Air Vent Holes Access holes with doors should be placed in the bottom slab if necessary to inspect utilities inside cells (i.e., waterline, conduits, E.Q. restrainers, etc.). Figure 5.3.8-2 and 5.3.8-3 shows access hole and air vent hole details. Air vents are required when access holes are used.
July 2000
5.3-19
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
Figure 5.3.8-1
P65:DP/BDM5
5.3-20
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
Figure 5.3.8-2
July 2000
5.3-21
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Reinforced Concrete Box Girder Bridges
Figure 5.3.8-3
5.3-22
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures 5.4
Hinges and Inverted T-Beam Pier Caps
Hinges and Inverted T-Beam Pier Caps Hinges and inverted T-beam pier caps require special design and detailing considerations. Continuous hinge shelves (both top and bottom projecting shelves) and continuous ledges of inverted T-beam pier caps, which support girders, are shown in Figures 5.4-1 and 5.4-2 respectively. In each case, vertical tensile forces (hanger tension) act at the intersection of the web and the horizontal hinge shelf or ledge. In the ledges of inverted T-beam pier caps, passage of live loads may also cause reversing torsional stresses which together with conventional longitudinal shear and bending produce complex stress distributions in the ledges [10,11]. Provide minimum shelf or ledge support lengths (N, N1, and N2) and provide positive longitudinal linkage (e.g., earthquake restrainers) [12] in accordance with the current AASHTO seismic design requirements. A. Local Failure Modes In addition to conventional longitudinal bending and shearing forces, there are several local modes of failure which should be addressed in the design [10,11]. These are: shear friction failure, flexural failure, hanger tension failure, punching shear failure of the horizontal hinge shelf or ledge, and spalling under the bearing. Figure 5.4-3 shows these local failure modes and potential cracks. For all conditions, except for the bearing strength check, use φ=0.85. For the bearing strength check, use φ=0.7 [13].
Continuous Hinge Figure 5.4-1
July 2000
5.4-1
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Hinges and Inverted T-Beam Pier Caps
Inverted T-Beam Pier Cap Figure 5.4-2
5.4-2
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Hinges and Inverted T-Beam Pier Caps
The forces acting on the hinge shown in Figure 5.4-3 are: shear, Vu; horizontal tensile force, Nuc; and moment, Mu. Vu
= Factored Shear (Dead Load + Live Load + Impact)
(1)
Nuc
≥ 0.2Vu, but less than 1.0Vu
(2)
Mu
= Vu(af) + Nuc(h-d)
(3)
where: af
= Flexural moment arm is the distance from the reaction to the centerline of the hanger reinforcement, and shall include the thermal movement of the reaction, Vu.
h-d
= Moment arm for the horizontal load, Nuc.
The horizontal tensile load, Nuc, is due to indeterminate causes such as restrained shrinkage or temperature stresses and is considered a live load [13]. In addition, service load conditions should also be checked for deflections and crack control.
Crack 1
could lead to a flexural or shear friction failure mode.
Crack 2
necessitates hanger reinforcement.
Crack 3
could lead to a punching shear failure.
Crack 4
can be avoided by reducing the bearing stress or allowing more edge distance. Failure Modes and Potential Cracks Figure 5.4-3
July 2000
5.4-3
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Hinges and Inverted T-Beam Pier Caps
B. Shear Friction Design 1.
Interior Bearing Figure 5.4-4 shows the effective shelf width used to compute the allowable shear strength. The ratio av/d shall satisfy equation (4) and the factored shear force (including shelf dead load) shall satisfy both equations (5) and (6) [13]: av/d ≤ 1.0
(4)
Vu ≤ φ (0.2fc′)(W+4av)(d)
(5)
Vu ≤ φµ (Avf)(fy)
(6)
where:
av d φ 0.2fc′ W+4av µ Avf
= = = ≤ = =
Distance from the reaction to the vertical face Depth from compression face to tensile reinforcement 0.85 800 psi Effective shelf width 1.4 for cast-in-place concrete (e.g., monolithic construction, no construction joint) = Shear friction reinforcement
When W+4av > S, check: Vu ≤ φ (0.2fc′)(S)(d) 2.
(7)
Bearing at End of Hinge or Ledge When S > 2c < (W+4av), check: Vu ≤ φ (0.2fc′)(2c)(d)
(8)
When S > (W+4av) < 2c, check: Vu ≤ φ (0.2fc′)(W+4av)(d)
(9)
When (W+4av) > S > 2c, check: Vu ≤ φ (0.2fc′)(S)(d)
(10)
In addition, equation (6) shall be satisfied. Avf is distributed over 2c, W+4av, or S, whichever is less. where
c = Distance from the end of the hinge or ledge to the center of the exterior bearing. S = Center-to-center of girders or hinge seat bearings.
5.4-4
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Hinges and Inverted T-Beam Pier Caps
Shear Friction Design Figure 5.4-4 C. Flexural Design (Figure 5.4-5) The primary reinforcement, As, for the shelf or ledge shall be determined from equations (11), (12), and (13), whichever is greater [13]: As ≥ Af + An
(11)
As ≥ 2(Avf)/3 + An
(12)
As ≥ ρmin (W+5af)(d)
(13)
where: ρmin = 0.04(fc′/fy) Af = Flexural reinforcement required for Mu Avf = Shear friction reinforcement An = Tensile reinforcement = Nuc/φ(fy) In addition, closed stirrups or ties parallel to As with a total area Ah of not less than 0.5(As-An) shall be uniformly distributed within two thirds of the effective depth adjacent to As [13]. If the effective width W+5af≥S place the reinforcement over distance S. At the ends of the hinge or ledge, distribute the reinforcement over distance 2c, S, or W+5af, whichever is less.
July 2000
5.4-5
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Hinges and Inverted T-Beam Pier Caps
Flexural Design Figure 5.4-5 D. Hanger Tension Design (Figure 5.4-6) The hanger tension reinforcement, Ahr, shall satisfy both of the following strength and serviceability equations: Vu ≤ φAhr/s)(fy)(S) V ≤ (Ahr/s)(0.5fy)(W+3av)
Strength Serviceability
(14) (15)
where: Ahr = Hanger reinforcement in square inches s = Spacing of the hanger reinforcement V = Service load reaction W+3av = Effective width for hanger reinforcement-Serviceability
Hinge Hanger Reinforcement Figure 5.4-6
5.4-6
July 2000
BRIDGE DESIGN MANUAL Criteria Reinforced Concrete Superstructures
Hinges and Inverted T-Beam Pier Caps
In addition to equations (14) and (15), the following equation shall also be satisfied for inverted T-beam pier caps (see Figure 5.4-7): 2Vu ≤ 2[2φ √ fc′ bfdf] + φ(ahr/s)(fy)(W+2df) where
(16)
bf = Width of bottom flange of inverted T-beam df = Distance from top of ledge to center of longitudinal cap reinforcement near the bottom flange of the inverted T-beam W+2df = Effective width for hanger reinforcement for inverted T-beam.
If S>(W+2df), it is not necessary to add the stirrup reinforcement for conventional shear and torsion to the hanger reinforcement. Ensure that the stirrup reinforcement satisfies either the conventional longitudinal shear and torsion reinforcement requirements or the hanger reinforcement requirement, whichever is greater. If S #9, area and weight are based on the decimal diameter. Table 5.1-A1
July 2000
5.1-A1
BRIDGE DESIGN MANUAL Appendix A Reinforced Concrete Superstructures
Bar Area vs. Bar Spacing
(Reinforcing Bars
AASHTO M31)
Bar Size
#3
#4
#5
#6
#7
Spacing 3″
0.44
0.80
3 1 /4
0.41
0.74
1.14
3 1 /2
0.38
0.69
3 3 /4
0.35
4
#8
#9
#10
#11
1.06
1.51
2.06
0.64
0.99
1.41
1.92
2.53
3.20
0.33
0.60
0.93
1.32
1.80
2.37
4 1 /4
0.31
0.56
0.88
1.24
1.69
4 1 /2
0.29
0.53
0.83
1.17
4 3 /4
0.28
0.51
0.78
5
0.26
0.48
5 1 /4
0.25
5 1 /2
#14
#18
3.00
3.81
4.68
2.23
2.82
3.59
4.40
1.60
2.11
2.67
3.39
4.16
6.00
1.11
1.52
2.00
2.53
3.21
3.94
5.68
0.74
1.06
1.44
1.90
2.40
3.05
3.74
5.40
0.46
0.71
1.01
1.37
1.81
2.29
2.90
3.57
5.14
0.24
0.44
0.68
0.96
1.31
1.72
2.18
2.77
3.40
4.91
5 3 /4
0.23
0.42
0.65
0.92
1.25
1.65
2.09
2.65
3.26
4.70
8.35
6
0.22
0.40
0.62
0.88
1.20
1.58
2.00
2.54
3.12
4.50
8.00
6 1 /2
0.20
0.37
0.57
0.81
1.11
1.46
1.85
2.35
2.88
4.15
7.38
7
0.19
0.34
0.53
0.75
1.03
1.35
1.71
2.18
2.67
3.86
6.86
7 1 /2
0.18
0.32
0.50
0.70
0.96
1.26
1.60
2.03
2.50
3.60
6.40
8
0.17
0.30
0.47
0.66
0.90
1.19
1.50
1.91
2.34
3.38
6.00
8 1 /2
0.16
0.28
0.44
0.62
0.85
1.12
1.41
1.79
2.20
3.18
5.65
9
0.15
0.27
0.41
0.59
0.80
1.05
1.33
1.69
2.08
3.00
5.33
9 1 /2
0.14
0.25
0.39
0.56
0.76
1.00
1.26
1.60
1.97
2.84
5.05
10
0.13
0.24
0.37
0.53
0.72
0.95
1.20
1.52
1.87
2.70
4.80
101/2
0.13
0.23
0.35
0.50
0.69
0.90
1.14
1.45
1.78
2.57
4.57
11
0.12
0.22
0.34
0.48
0.65
0.86
1.09
1.39
1.70
2.45
4.36
111/2
0.11
0.21
0.32
0.46
0.63
0.82
1.04
1.33
1.63
2.35
4.17
As Per Foot of Bar Table 5.1-A2
5.1-A2
July 2000
BRIDGE DESIGN MANUAL Appendix A Reinforced Concrete Superstructures
Bar Area vs. Number of Bars
Size No.
#3
#4
#5
#6
#7
#8
#9
1
0.11
0.20
0.31
0.44
0.60
0.79
1.00
2
0.22
0.40
0.62
0.88
1.20
1.58
3
0.33
0.60
0.93
1.32
1.80
4
0.44
0.80
1.24
1.76
5
0.55
1.00
1.55
6
0.66
1.20
7
0.77
8
#10
#11
#14
#18
1.27
1.56
2.25
4.00
2.00
2.54
3.12
4.50
8.00
2.37
3.00
3.81
4.68
6.75
12.00
2.40
3.16
4.00
5.08
6.24
9.00
16.00
2.20
3.00
3.95
5.00
6.35
7.80
11.25
20.00
1.86
2.64
3.60
4.74
6.00
7.62
9.36
13.50
24.00
1.40
2.17
3.08
4.20
5.53
7.00
8.89
10.92
15.75
28.00
0.88
1.60
2.48
3.52
4.80
6.32
8.00
10.16
12.48
18.00
32.00
9
0.99
1.80
2.79
3.96
5.40
7.11
9.00
11.43
14.04
20.25
36.00
10
1.10
2.00
3.10
4.40
6.00
7.90
10.00
12.70
15.60
22.50
40.00
11
1.21
2.20
3.41
4.84
6.60
8.69
11.00
13.97
17.16
24.75
44.00
12
1.32
2.40
3.72
5.28
7.20
9.48
12.00
15.24
18.72
27.00
48.00
13
1.43
2.60
4.03
5.72
7.80
10.27
13.00
16.51
20.28
29.25
52.00
14
1.54
2.80
4.34
6.16
8.40
11.06
14.00
17.78
21.84
31.50
56.00
15
1.65
3.00
4.65
6.60
9.00
11.85
15.00
19.05
23.40
33.75
60.00
16
1.76
3.20
4.96
7.04
9.60
12.64
16.00
20.32
24.96
36.00
64.00
17
1.87
3.40
5.27
7.48
10.20
13.43
17.00
21.59
26.52
38.25
68.00
18
1.98
3.60
5.58
7.92
10.80
14.22
18.00
22.86
28.08
40.50
72.00
19
2.09
3.80
5.89
8.36
11.40
15.01
19.00
24.13
29.64
42.75
76.00
20
2.20
4.00
6.20
8.80
12.00
15.80
20.00
25.40
31.20
45.00
80.00
21
2.31
4.20
6.51
9.24
12.60
16.59
21.00
26.67
32.76
47.25
84.00
22
2.42
4.40
6.82
9.68
13.20
17.38
22.00
27.94
34.32
49.50
88.00
23
2.53
4.60
7.13
10.12
13.80
18.17
23.00
29.21
35.88
51.75
92.00
24
2.64
4.80
7.44
10.56
14.40
18.96
24.00
30.48
37.44
54.00
96.00
25
2.75
5.00
7.75
11.00
15.00
19.75
25.00
31.75
39.00
56.25
100.00
26
2.86
5.20
8.06
11.44
15.60
20.54
26.00
33.02
40.56
58.50
104.00
27
2.97
5.40
8.37
11.88
16.20
21.33
27.00
34.29
42.12
60.75
108.00
28
3.08
5.60
8.68
12.32
16.80
22.12
28.00
35.56
43.68
63.00
112.00
29
3.19
5.80
8.99
12.76
17.40
22.91
29.00
36.83
45.24
65.25
116.00
30
3.30
6.00
9.30
13.20
18.00
23.70
30.00
38.10
46.80
67.50
120.00
Areas for Various Bar Sizes and Number of Bars Table 5.1-A3
July 2000
5.1-A3
BRIDGE DESIGN MANUAL Appendix A Reinforced Concrete Superstructures Tension Development Length of Uncoated Deformed Bars fc′ = 3,000 psi
fc′ = 4,000 psi
fc′ = 5,000 psi
fc′ = 6,000 psi
Bar Size
Top Bars ft-in
Others ft-in
Top Bars ft-in
Others ft-in
Top Bars ft-in
Others ft-in
Top Bars ft-in
Others ft-in
3 4 5 6 7 8 9 10 11 14 18
1′-5″ 1′-5″ 1′-9″ 2′-3″ 3′-1″ 4′-1″ 5′-2″ 6′-6″ 8′-0″ 10′-11″ 14′-1″
1′-0″ 1′-0″ 1′-3″ 1′-8″ 2′-3″ 2′-11″ 3′-8″ 4′-8″ 5′-9″ 7′-10″ 10′-1″
1′-5″ 1′-5″ 1′-9″ 2′-2″ 2′-8″ 3′-6″ 4′-6″ 5′-8″ 6′-11″ 9′-5″ 12′-3″
1′-0″ 1′-0″ 1′-3″ 1′-6″ 1′-11″ 2′-6″ 3′-2″ 4′-1″ 5′-0″ 9′-9″ 8′-9″
1′-5″ 1′-5″ 1′-9″ 2′-2″ 2′-6″ 3′-2″ 4′-0″ 5′-1″ 6′-3″ 8′-5″ 10′-11″
1′-0″ 1′-0″ 1′-3″ 1′-6″ 1′-9″ 2′-3″ 2′-10″ 3′-8″ 4′-5″ 6′-1″ 7′-10″
1′-5″ 1′-5″ 1′-9″ 2′-2″ 2′-6″ 2′-11″ 3′-8″ 4′-8″ 5′-8″ 7′-9″ 10′-0″
1′-0″ 1′-0″ 1′-3″ 1′-6″ 1′-9″ 2′-1″ 2′-7″ 3′-4″ 4′-1″ 5′-6″ 7′-2″
Tension Development Length of Epoxy Coated Deformed Bars fc′ = 3,000 psi
fc′ = 4,000 psi
fc′ = 5,000 psi
fc′ = 6,000 psi
Bar Size
Top Bars ft-in
Others ft-in
Top Bars ft-in
Others ft-in
Top Bars ft-in
Others ft-in
Top Bars ft-in
Others ft-in
3 4 5 6 7 8 9 10 11 14 18
1′-9″ 1′-9″ 2′-2″ 2′-9″ 3′-9″ 4′-11″ 6′-3″ 7′-11″ 9′-9″ 13′-3″ 17′-1″
1′-6″ 1′-6″ 1′-11″ 2′-5″ 3′-4″ 4′-4″ 5′-6″ 7′-0″ 8′-7″ 11′-8″ 15′-1″
1′-9″ 1′-9″ 2′-2″ 2′-7″ 3′-3″ 4′-3″ 5′-5″ 6′-10″ 8′-5″ 11′-6″ 14′-10″
1′-6″ 1′-6″ 1′-11″ 2′-3″ 2′-11″ 3′-9″ 4′-9″ 6′-1″ 7′-5″ 10′-1″ 13′-1″
1′-9″ 1′-9″ 2′-2″ 2′-7″ 3′-0″ 3′-10″ 4′-10″ 6′-2″ 7′-6″ 10′-3″ 13′-3″
1′-6″ 1′-6″ 1′-11″ 2′-3″ 2′-8″ 3′-5″ 4′-3″ 5′-5″ 6′-8″ 9′-1″ 11′-8″
1′-9″ 1′-9″ 2′-2″ 2′-7″ 3′-0″ 3′-6″ 4′-5″ 5′-7″ 6′-11″ 9′-4″ 12′-1″
1′-6″ 1′-6″ 1′-11″ 2′-3″ 2′-8″ 3′-1″ 3′-11″ 4′-11″ 6′-1″ 8′-3″ 10′-8″
Top Bars are so placed that more than 12″ of concrete is cast below the reinforcement. Modification Factor for Spacing >=6″ and side cover >=3″ = 0.8. Minimum Development Length = 12″. Modification Factor for Reinforcement Enclosed in Spiral = 0.75
Table 5.1-A4
Tension Development Length of Standard 90° and 180° Hooks fc′ = 3,000 psi
Bar Size
3 4 5 6 7 8 9 10 11 14 18
Side Cover Side Cover < 21/2″ Cover >= 21/2″ Cover on Tail < 2″ on Tail >= 2″
0′-9″ 0′-11″ 1′-2″ 1′-5″ 1′-8″ 1′-10″ 2′-1″ 2′-4″ 2′-7″ 3′-1″ 4′-2″
0′-6″ 0′-8″ 0′-10″ 1′-0″ 1′-2″ 1′-4″ 1′-6″ 1′-8″ 1′-10″ 3′-1″ 4′-2″
fc′ = 4,000 psi
fc′ = 5,000 psi
Side Cover Side Cover Side Cover Side Cover < 21/2″ Cover >= 21/2″ Cover < 21/2″ Cover >= 21/2″ Cover on Tail < 2″ on Tail >= 2″ on Tail < 2″ on Tail >= 2″
0′-8″ 0′-10″ 1′-0″ 1′-3″ 1′-5″ 1′-7″ 1′-10″ 2′-1″ 2′-3″ 2′-9″ 3′-7″
0′-6″ 0′-7″ 0′-9″ 0′-10″ 1′-0″ 1′-2″ 1′-3″ 1′-5″ 1′-7″ 2′-9″ 3′-7″
0′-7″ 0′-9″ 0′-11″ 1′-1″ 1′-3″ 1′-5″ 1′-8″ 1′-10″ 2′-0″ 2′-5″ 3′-3″
0′-6″ 0′-7″ 0′-8″ 0′-9″ 0′-11″ 1′-0″ 1′-2″ 1′-3″ 1′-5″ 2′-5″ 3′-3″
fc′ = 6,000 psi
Side Cover Side Cover < 21/2″ Cover >= 21/2″ Cover on Tail < 2″ on Tail >= 2″
0′-6″ 0′-8″ 0′-10″ 1′-0″ 1′-2″ 1′-4″ 1′-6″ 1′-8″ 1′-10″ 2′-3″ 2′-11″
0′-6″ 0′-7″ 0′-7″ 0′-8″ 0′-10″ 0′-11″ 1′-1″ 1′-2″ 1′-4″ 2′-3″ 2′-11″
Table 5.1-A5
5.1-A4
July 2000
BRIDGE DESIGN MANUAL Appendix A Reinforced Concrete Superstructures Tension Lap Splice Lengths of Grade 60 Uncoated Bars – Class B fc′ = 3,000 psi Bar Size
3 4 5 6 7 8 9 10 11 14 18
Top Bars ft-in
Others ft-in
2′-0″ 2′-0″ 2′-0″ 2′-0″ 2′-4″ 2′-0″ 2′-11″ 2′-1″ 4′-0″ 2′-11″ 5′-3″ 3′-9″ 6′-8″ 4′-9″ 8′-6″ 6′-1″ 10′-5″ 7′-5″ Lap Splices Not Allowed
fc′ = 4,000 psi Top Bars ft-in
Others ft-in
2′-0″ 2′-0″ 2′-0″ 2′-0″ 2′-4″ 2′-0″ 2′-9″ 2′-0″ 3′-6″ 2′-6″ 4′-7″ 3′-3″ 5′-9″ 4′-2″ 7′-4″ 5′-3″ 9′-0″ 6′-5″ Lap Splices Not Allowed
fc′ = 5,000 psi Top Bars ft-in
Others ft-in
2′-0″ 2′-0″ 2′-0″ 2′-0″ 2′-4″ 2′-0″ 2′-9″ 2′-0″ 3′-3″ 2′-4″ 4′-11″ 2′-11″ 5′-2″ 3′-9″ 6′-7″ 4′-8″ 8′-1″ 5′-9″ Lap Splices Not Allowed
fc′ = 6,000 psi Top Bars ft-in
Others ft-in
2′-0″ 2′-0″ 2′-0″ 2′-0″ 2′-4″ 2′-0″ 2′-9″ 2′-0″ 3′-3″ 2′-4″ 3′-9″ 2′-8″ 4′-9″ 3′-5″ 6′-0″ 4′-4″ 7′-4″ 5′-3″ Lap Splices Not Allowed
Tension Lap Splice Lengths of Grade 60 Epoxy Coated Bars – Class B fc′ = 3,000 psi Bar Size
3 4 5 6 7 8 9 10 11 14 18
Top Bars ft-in
Others ft-in
2′-3″ 2′-0″ 2′-3″ 2′-0″ 2′-10″ 2′-6″ 3′-7″ 3′-2″ 4′-11″ 4′-4″ 6′-5″ 5′-8″ 8′-1″ 7′-2″ 10′-3″ 9′-1″ 12′-8″ 11′-2″ Lap Splices Not Allowed
fc′ = 4,000 psi Top Bars ft-in
Others ft-in
2′-3″ 2′-0″ 2′-3″ 2′-0″ 2′-10″ 2′-6″ 3′-4″ 3′-0″ 4′-3″ 3′-9″ 5′-7″ 4′-11″ 7′-0″ 6′-2″ 8′-11″ 7′-10″ 10′-11″ 9′-8″ Lap Splices Not Allowed
fc′ = 5,000 psi Top Bars ft-in
Others ft-in
2′-3″ 2′-0″ 2′-3″ 2′-0″ 2′-10″ 2′-6″ 3′-4″ 3′-0″ 3′-11″ 3′-5″ 5′-0″ 4′-5″ 6′-3″ 5′-7″ 8′-0″ 7′-0″ 9′-9″ 8′-0″ Lap Splices Not Allowed
fc′ = 6,000 psi Top Bars ft-in
Others ft-in
2′-3″ 2′-0″ 2′-3″ 2′-0″ 2′-10″ 2′-6″ 3′-4″ 3′-0″ 3′-11″ 3′-5″ 4′-6″ 4′-0″ 5′-9″ 5′-1″ 7′-3″ 6′-5″ 8′-11″ 7′-11″ Lap Splices Not Allowed
Top Bars are so placed that more than 12″ of concrete is cast below the reinforcement. Definition of Splice Classes:
Class A: Class B: Class C:
Low stressed bars – 75% or less are spliced Low stressed bars – more than 75% are spliced High stressed bars – 1/2 or less are spliced High stressed bars – more than 50% are spliced
Class B Lap splice is the preferred and most commonly used by bridge office. Modification Factor for Class A: 0.77 Modification Factor for Class C: 1.31 Modification Factor for 3-bar Bundle = 1.2
Table 5.1-A6
July 2000
5.1-A5
BRIDGE DESIGN MANUAL Appendix A Minimum Development Length and Minimum Lap Splices of Deformed Bars in Compression
Reinforced Concrete Superstructures
Development Length of Deformed Bars in Compression and Minimum Compression Lap Splice Per AASHTO Standard Specifications, 1991, 16th Edition Articles 8.26, 8.32.4 Concrete Reinf.
fc′ = 3,000 psi fc′ = 4,000 psi fc′ = 5,000 psi fc′ = 6,000 psi fc′ > 3,000 psi Grade 60
Bar Size
Grade 60
Grade 60
Grade 60
Grade 60 Minimum Lap Splice
Development Length, ld
3&4
1′-0″*
1′-0″*
1′-0″*
1′-0″*
2′-0″4
5
1′-2″
1′-0″
1′-0″*
1′-0″*
2′-0″4
6
1′-5″
1′-3″
1′-2″
1′-2″
2′-0″4
7
1′-8″
1′-5″
1′-4″
1′-4″
2′-3″
8
1′-10″
1′-7″
1′-6″
1′-6″
2′-6″
9
2′-1″
1′-10″
1′-9″
1′-9″
2′-10″
10
2′-4″
2′-1″
1′-11″
1′-11″
3′-3″
11
2′-7″
2′-3″
2′-2″
2′-2″
3′-7″
14
3′-1″
2′-9″
2′-7″
2′-7″
4′-3″
18
4′-2″
3′-7″
3′-5″
3′-5″
5′-8″
Note: 1. Where excess bar area is provided, ld may be reduced by the ratio of required area to area provided. 2. *1′-0″ minimum (office practice). 3. ld (compression) must be developed with straight bar extension. Reduced length noted in (1) shall also be straight bar extension. 4. 2′-0″ minimum (office practice). 5. When splicing smaller bars to larger bars, the lap splice shall be the larger of the minimum compression lap splice or the development length of the larger bar in compression, AASHTO Art. 8.32.4.1. Table 5.1-A7
5.1-A6
July 2000
BRIDGE DESIGN MANUAL Appendix A Reinforced Concrete Superstructures
ρ
Mu φbd2
0.0010 0.0011 0.0012 0.0013 0.0014 0.0015 0.0016 0.0017 0.0018 0.0019 0.0020 0.0021 0.0022 0.0023 0.0024 0.0025 0.0026 0.0027 0.0028 0.0029 0.0030 0.0031 0.0032 0.0033 0.0034 0.0035 0.0036 0.0037 0.0038 0.0039 0.0040 0.0041 0.0042 0.0043 0.0044 0.0045 0.0046 0.0047 0.0048 0.0049 0.0050 0.0051 0.0052
59.3 65.1 71.0 76.8 82.6 88.4 94.2 100.0 105.7 111.4 117.2 122.9 128.6 134.3 139.9 145.6 151.2 156.8 162.4 168.0 173.6 179.2 184.8 190.3 195.8 201.3 206.8 212.3 217.8 223.2 228.7 234.1 239.5 244.9 250.3 255.7 261.0 266.4 271.7 277.0 282.3 287.6 292.9
ρ
Mu φbd2
ρ
0.0053 0.0054 0.0055 0.0056 0.0057 0.0058 0.0059 0.0060 0.0061 0.0062 0.0063 0.0064 0.0065 0.0066 0.0067 0.0068 0.0069 0.0070 0.0071 0.0072 0.0073 0.0074 0.0075 0.0076 0.0077 0.0078 0.0079 0.0080 0.0081 0.0082 0.0083 0.0084 0.0085 0.0086 0.0087 0.0088 0.0089 0.0090 0.0091 0.0092 0.0093 0.0094 0.0095 0.0096
298.1 303.4 308.6 313.8 319.0 324.2 329.4 334.5 339.7 344.8 349.9 355.0 360.1 365.2 370.2 375.3 380.3 385.3 390.3 395.0 400.3 405.2 410.2 415.1 420.0 424.9 429.8 434.7 439.5 444.4 449.2 454.0 458.8 463.6 468.4 473.2 477.9 482.6 487.4 492.1 496.8 501.4 506.1 510.7
0.0097 0.0098 0.0099 0.0100 0.0101 0.0102 0.0103 0.0104 0.0105 0.0106 0.0107 0.0108 0.0109 0.0110 0.0111 0.0112 0.0113 0.0114 0.0115 0.0116 0.0117 0.0118 0.0119 0.0120 0.0121 0.0122 0.0123 0.0124 0.0125 0.0126 0.0127 0.0128 0.0129 0.0130 0.0131 0.0132 0.0133 0.0134 0.0135 0.0136 0.0137 0.0138 0.0139 0.0140
ρ Values for Singly Reinforced Beams fc′ = 3,000 psi fy = 60,000 psi Mu φbd2
ρ
515.4 0.0141 520.0 0.0142 524.6 0.0143 529.2 0.0144 533.8 0.0145 538.3 0.0146 542.9 0.0147 547.4 0.0148 551.9 0.0149 556.4 0.0150 560.9 0.0151 565.4 0.0152 569.9 0.0153 574.3 0.0154 578.8 0.0155 583.2 0.0156 587.6 0.0157 592.0 0.0158 596.4 0.0159 600.7 0.0160 605.1 ρmax 0.0161 609.4 613.7 618.0 622.3 626.6 630.9 635.1 639.4 643.6 647.8 652.0 656.2 660.3 664.5 668.6 672.8 676.9 681.0 685.0 689.1 693.2 697.2 701.2
Mu φbd2 705.2 709.2 713.2 717.2 721.1 725.1 729.0 732.9 736.8 740.7 744.6 748.4 752.3 756.1 759.9 763.7 767.5 771.2 775.0 778.7 782.5
Notes: Mu 1. Units of ρbd2 are in psi. 2. ρmin should be based on 1.2 Mcr or 1.33 ρ analysis, whichever is smaller. 3. ρmax = 0.75ρb = 0.0161 based on β1 = 0.85.
Table 5.2-A1
July 2000
5.2-A1
BRIDGE DESIGN MANUAL Appendix A Reinforced Concrete Superstructures ρ 0.0010 0.0011 0.0012 0.0013 0.0014 0.0015 0.0016 0.0017 0.0018 0.0019 0.0020 0.0021 0.0022 0.0023 0.0024 0.0025 0.0026 0.0027 0.0028 0.0029 0.0030 0.0031 0.0032 0.0033 0.0034 0.0035 0.0036 0.0037 0.0038 0.0039 0.0040 0.0041 0.0042 0.0043 0.0044 0.0045 0.0046 0.0047 0.0048 0.0049 0.0050 0.0051 0.0052 0.0053 0.0054 0.0055
Mu φbd2 59.5 65.4 71.2 77.1 83.0 88.8 94.6 100.5 106.3 112.1 117.9 123.7 129.4 135.2 140.9 146.7 152.4 158.1 163.8 169.5 175.2 180.9 186.6 192.2 197.9 203.5 209.1 214.7 220.3 225.9 231.5 237.1 242.6 248.2 253.7 259.2 264.8 270.3 275.8 281.2 286.7 292.2 297.6 303.1 308.5 313.9
ρ 0.0056 0.0057 0.0058 0.0059 0.0060 0.0061 0.0062 0.0063 0.0064 0.0065 0.0066 0.0067 0.0068 0.0069 0.0070 0.0071 0.0072 0.0073 0.0074 0.0075 0.0076 0.0077 0.0078 0.0079 0.0080 0.0081 0.0082 0.0083 0.0084 0.0085 0.0086 0.0087 0.0088 0.0089 0.0090 0.0091 0.0092 0.0093 0.0094 0.0095 0.0096 0.0097 0.0098 0.0099 0.0100 0.0101
Mu φbd2 319.3 324.7 330.1 335.5 340.9 346.2 351.6 356.9 362.2 367.6 372.9 378.2 383.4 388.7 394.0 399.2 404.5 409.7 414.9 420.1 425.3 430.5 435.7 440.9 446.0 451.2 456.3 461.4 466.5 471.6 476.7 481.8 486.9 491.9 497.0 502.0 507.1 512.1 517.1 522.1 527.1 532.0 537.0 542.0 546.9 551.8
ρ 0.0102 0.0103 0.0104 0.0105 0.0106 0.0107 0.0108 0.0109 0.0110 0.0111 0.0112 0.0113 0.0114 0.0115 0.0116 0.0117 0.0118 0.0119 0.0120 0.0121 0.0122 0.0123 0.0124 0.0125 0.0126 0.0127 0.0128 0.0129 0.0130 0.0131 0.0132 0.0133 0.0134 0.0135 0.0136 0.0137 0.0138 0.0139 0.0140 0.0141 0.0142 0.0143 0.0144 0.0145 0.0146 0.0147
Mu φbd2 556.7 561.7 566.6 571.5 576.3 581.2 586.1 590.9 595.7 600.6 605.4 610.2 615.0 619.8 624.5 629.3 634.1 638.8 643.5 648.2 653.0 657.7 662.3 667.0 671.7 676.3 681.0 685.6 690.3 694.9 699.5 704.1 708.6 713.2 717.8 722.3 726.9 731.4 735.9 740.4 744.9 749.4 753.9 758.3 762.8 767.2
ρ Values for Singly Reinforced Beams fc′ = 4,000 psi fy = 60,000 psi
ρ 0.0148 0.0149 0.0150 0.0151 0.0152 0.0153 0.0154 0.0155 0.0156 0.0157 0.0158 0.0159 0.0160 0.0161 0.0162 0.0163 0.0164 0.0165 0.0166 0.0167 0.0168 0.0169 0.0170 0.0171 0.0172 0.0173 0.0174 0.0175 0.0176 0.0177 0.0178 0.0179 0.0180 0.0181 0.0182 0.0183 0.0184 0.0185 0.0186 0.0187 0.0188 0.0189 0.0190 0.0191 0.0192 0.0193
Mu φbd2 771.7 776.1 780.5 784.9 789.3 793.7 798.1 802.4 806.8 811.1 815.4 819.7 824.1 828.3 832.6 836.9 841.2 845.4 849.7 853.9 858.1 862.3 866.5 870.7 874.9 879.1 883.2 887.4 891.5 895.6 899.7 903.9 907.9 912.0 916.1 920.2 924.2 928.3 932.3 936.3 940.3 944.3 948.3 952.3 956.2 960.2
ρ 0.0194 0.0195 0.0196 0.0197 0.0198 0.0199 0.0200 0.0201 0.0202 0.0203 0.0204 0.0205 0.0206 0.0207 0.0208 0.0209 0.0210 0.0211 0.0212 0.0213 ρmax 0.0214
Mu φbd2 964.1 968.1 972.0 975.9 979.8 983.7 987.6 991.5 995.3 999.2 1003.0 1006.8 1010.7 1014.5 1018.3 1022.0 1025.8 1029.6 1033.3 1037.1 1040.8
Notes: Mu 1. Units of ρbd2 are in psi. 2. ρmin should be based on 1.2 Mcr or 1.33 ρ analysis, whichever is smaller. 3. ρmax = 0.75ρb = 0.0214 based on β1 = 0.85.
Table 5.2-A2
5.2-A2
July 2000
BRIDGE DESIGN MANUAL
ρ Values for Singly Reinforced Beams fc′ = 5,000 psi fy = 60,000 psi
Appendix A Reinforced Concrete Superstructures ρ 0.0010 0.0011 0.0012 0.0013 0.0014 0.0015 0.0016 0.0017 0.0018 0.0019 0.0020 0.0021 0.0022 0.0023 0.0024 0.0025 0.0026 0.0027 0.0028 0.0029 0.0030 0.0031 0.0032 0.0033 0.0034 0.0035 0.0036 0.0037 0.0038 0.0039 0.0040 0.0041 0.0042 0.0043 0.0044 0.0045 0.0046 0.0047 0.0048 0.0049 0.0050 0.0051 0.0052 0.0053 0.0054 0.0055 0.0056 0.0057 0.0058 0.0059 0.0060
Mu φbd2 59.6 65.5 71.4 77.3 83.2 89.0 94.9 100.8 106.6 112.5 118.3 124.1 129.9 135.8 141.6 147.3 153.1 158.9 164.7 170.4 176.2 181.9 187.7 193.4 199.1 204.8 210.5 216.2 221.9 227.5 233.2 238.9 244.5 250.1 255.8 261.4 267.0 272.6 278.2 283.8 289.4 295.0 300.5 306.1 311.6 317.1 322.7 328.2 333.7 339.2 344.7
ρ 0.0061 0.0062 0.0063 0.0064 0.0065 0.0066 0.0067 0.0068 0.0069 0.0070 0.0071 0.0072 0.0073 0.0074 0.0075 0.0076 0.0077 0.0078 0.0079 0.0080 0.0081 0.0082 0.0083 0.0084 0.0085 0.0086 0.0087 0.0088 0.0089 0.0090 0.0091 0.0092 0.0093 0.0094 0.0095 0.0096 0.0097 0.0098 0.0099 0.0100 0.0101 0.0102 0.0103 0.0104 0.0105 0.0106 0.0107 0.0108 0.0109 0.0110 0.0111 0.0112
Mu φbd2 350.2 355.7 361.1 366.6 372.1 377.5 382.9 388.4 393.8 399.2 404.6 410.0 415.4 420.7 426.1 431.5 436.8 442.2 447.5 452.8 458.1 463.4 468.7 474.0 479.3 484.6 489.8 495.1 500.4 505.6 510.8 516.0 521.3 526.5 531.7 536.9 542.0 547.2 552.4 557.5 562.7 567.8 572.9 578.1 583.2 588.3 593.4 598.5 603.5 608.6 613.7 618.7
ρ 0.0113 0.0114 0.0115 0.0116 0.0117 0.0118 0.0119 0.0120 0.0121 0.0122 0.0123 0.0124 0.0125 0.0126 0.0127 0.0128 0.0129 0.0130 0.0131 0.0132 0.0133 0.0134 0.0135 0.0136 0.0137 0.0138 0.0139 0.0140 0.0141 0.0142 0.0143 0.0144 0.0145 0.0146 0.0147 0.0148 0.0149 0.0150 0.0151 0.0152 0.0153 0.0154 0.0155 0.0156 0.0157 0.0158 0.0159 0.0160 0.0161 0.0162 0.0163 0.0164
Mu φbd2
ρ
623.8 628.8 633.8 638.8 643.8 648.9 653.8 658.8 663.8 668.8 673.7 678.7 683.6 688.6 693.5 698.4 703.3 708.2 713.1 718.0 722.9 727.7 732.6 737.4 742.3 747.1 751.9 756.7 761.5 766.3 771.1 775.9 780.7 785.4 790.2 795.0 799.7 804.4 809.1 813.9 818.6 823.3 827.9 832.6 837.3 842.0 846.6 851.3 855.9 860.5 865.1 869.7
0.0165 0.0166 0.0167 0.0168 0.0169 0.0170 0.0171 0.0172 0.0173 0.0174 0.0175 0.0176 0.0177 0.0178 0.0179 0.0180 0.0181 0.0182 0.0183 0.0184 0.0185 0.0186 0.0187 0.0188 0.0189 0.0190 0.0191 0.0192 0.0193 0.0194 0.0195 0.0196 0.0197 0.0198 0.0199 0.0200 0.0201 0.0202 0.0203 0.0204 0.0205 0.0206 0.0207 0.0208 0.0209 0.0210 0.0211 0.0212 0.0213 0.0214 0.0215 0.0216
Mu φbd2 874.3 878.9 883.5 888.1 892.7 897.2 901.8 906.3 910.9 915.4 919.9 924.4 928.9 933.4 937.9 942.4 946.8 951.3 955.7 960.2 964.6 969.0 973.5 977.9 982.3 986.6 991.0 995.4 999.8 1004.1 1008.5 1012.8 1017.1 1021.5 1025.8 1030.1 ρmax 1034.4 1038.7 1042.9 1047.2 1051.5 1055.7 1060.0 1064.2 1068.4 1072.7 1076.9 1081.1 1085.3 1089.5 1093.6 1097.8
ρ 0.0217 0.0218 0.0219 0.0220 0.0221 0.0222 0.0223 0.0224 0.0225 0.0226 0.0227 0.0228 0.0229 0.0230 0.0231 0.0232 0.0233 0.0234 0.0235 0.0236 0.0237 0.0238 0.0239 0.0240 0.0241 0.0242 0.0243 0.0244 0.0245 0.0246 0.0247 0.0248 0.0249 0.0250 0.0251 0.0252
Mu φbd2 1102.0 1106.1 1110.3 1114.4 1118.5 1122.6 1126.8 1130.9 1134.9 1139.0 1143.1 1147.2 1151.2 1155.3 1159.3 1163.4 1167.4 1171.4 1175.4 1179.4 1183.4 1187.4 1191.4 1195.3 1199.3 1203.2 1207.2 1211.1 1215.0 1218.9 1222.8 1226.7 1230.6 1234.5 1238.4 1242.2
Notes: Mu 1. Units of ρbd2 are in psi. 2. ρmin should be based on 1.2 Mcr or 1.33 ρ analysis, whichever is smaller. 3. ρmax = 0.75ρb = 0.0252 based on β1 = 0.80.
Table 5.2-A3
July 2000
5.2-A3
BRIDGE DESIGN MANUAL Appendix A Reinforced Concrete Superstructures
Positive Moment Reinforcement
Figure 5.3-A1
July 2000
5.3-A1
BRIDGE DESIGN MANUAL Appendix A Reinforced Concrete Superstructures
Negative Moment Reinforcement
Figure 5.3-A2
5.3-A2
July 2000
BRIDGE DESIGN MANUAL Appendix A
Adjusted Negative Moment Case I (Design for M @ Face of Effective Support)
Reinforced Concrete Superstructures
Figure 5.3-A3
July 2000
5.3-A3
BRIDGE DESIGN MANUAL Appendix A Adjusted Negative Moment Case II (Design for M @ 1/4 Point)
Reinforced Concrete Superstructures
Figure 5.3-A4
5.3-A4
July 2000
BRIDGE DESIGN MANUAL Appendix A Load Factor Slab Design fc′ = 4,000 psi
Reinforced Concrete Superstructures
Figure 5.3-A5
July 2000
5.3-A5
BRIDGE DESIGN MANUAL Appendix A Load Factor Slab Design fc′ = 5,000 psi
Reinforced Concrete Superstructures
Figure 5.3-A6
5.3-A6
July 2000
BRIDGE DESIGN MANUAL Appendix A Reinforced Concrete Superstructures
Slab Design — Traffic Barrier Load
Notes: 1.
Section “A-A” is taken to be the critical section. Other sections ordinarily do not need to be investigated.
2.
Provide enough extension to the left of “A-A” to develop the As required (usually will require hooking bars).
3.
Service Load fs = 20,000, Load Factor = (1.3D + 2.17L).
4.
For Load Factor design, check distribution of flexural reinforcement — AASHTO 8.16-8.4. If #5 or #6 bars are used to furnish the As from this chart, then this requirement will not have to be checked.
Figure 5.3-A7
July 2000
5.3-A7
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Slab Design
Example 5.2-B1 Given: Center-to-center spacing of girders = Width of top flange of steel girder = Deck concrete, Class 4000 fc′ = = Reinforcing steel, Grade 60 fy Cover to top bars = Cover to bottom bars = Analyze a 1 foot wide section of slab Find: 1.
12 feet 3 inches 18 inches wide 4,000 psi 60,000 psi 2.5 inches 1.0 inch
Deck thickness, deck reinforcement
Determine Deck Thickness Seff = 12.25′ – 2 (18″) / (4) (12) = 11.50′ Minimum thickness, tmin = (Seff + 10) (12) / 30 = (11.50 + 10) (12) / 30 = 8.60″ Use 83/4″ thick slab
2.
Determine Transverse Deck Reinforcement — Top Slab Reinforcement Dead Load Moment, MDL: MDL = (1/10) [ (8.75″ / 12) (0.160 kcf) ] (11.50)2 = 1.55 kip-ft/ft Live Load Moment + Impact, MLL+I: MLL+I =
(S + 2) (Pwheel) (0.8) (1.30) 32
AASHTO, 1989, Section 3.24.3.1
where: Pwheel = 1.25 (16 kips/wheel) = 20.0 kips/wheel (HS25 Truck) continuity factory = 0.8 impact factor = 1.30 (11.50 + 2) MLL+I = (20.0) (0.8) (1.30) = 8.78 kip-ft/ft 32
AASHTO, 1989, Section 3.24.3.1
Factored Design Moment, Mu: Mu = 1.3 [ 1.55 + (5/3) (8.78) ] = 21.04 kip-ft/ft Determine As req’d: dtop bars = 8.75 – 2.5 – (0.75) / 2 = 5.875″ Mu / (φ) (b) (d)2 = 21.04 (12,000) / (0.9) (12) (5.875)2 = 677.3 psi Interpolating from Table 5.2-A2, Appendix A: ρ = 0.01272 As req’d = ρ (b) (d) = 0.01272 (12) (5.875) = 0.90 in2/ft Use #6 bars at 5″ ctrs, As = 1.06 in2/ft > 0.90 in2/ft
ok
Use same bar size and spacing for bottom slab reinforcement. An alternate approach is to solve directly for As req’d from Eq (5), BDM Section 5.2.1B: As req’d = 0.85 (fc′ / fy) (b) [ d –
√d2 – (31.3725 Mu / fc′ b) ]
= [ 0.85 (4) (12) / 60 ] [ 5.875 – As req’d = 0.90 in2/ft
July 2000
(5)
√ (5.785)2 – 31.3725 (21.04) / (4) (12) ]
Agrees with value previously computed by tables.
5.2-B1-1
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Slab Design
Check As min using Table 5.2-A2, Appendix A: Mu = 1.2 Mcr = 1.2 fr S = (1.2) 7.5 √ fc′ (1/6) (b) (t)2 = (1.2) 7.5 √ 4,000 (1/6) (12) (8.75)2 87,160 in-lbs/ft Mu / φ bd2 = 87,160 / [ 0.9 (12) (5.875)2 ] = 233.8 psi From Table 5.2-A2, Appendix A, interpolate ρ = 0.00404 As min = ρ (b) (d) = 0.00404 (12) (5.875) = 0.28 in2/ft < 1.06 in2/ft Check As min using Eq (6): As min =
0.85 fc′ (b) fy
As min =
0.85 (4) (12) (60)
As min = 0.285 in2/ft Check As max:
( √ ( √ d –
d2 –
5.875 –
0.124 h2
√ f c′
(5.875)2 –
)
(6)
0.124 (8.75)2
√4
)
Agrees with value from tables.
From Table 5.2-A2, Appendix A, ρmax = 0.75 ρb = 0.0214
As max = 0.0214 (12) (5.875) = 1.51 in2/ft Check As max using Eq (7), BDM Section 5.2.1B:
As max 3.
fc′ fy
( 87 87+ f ) (4) 87 = 0.6375 (0.85) (12) (5.875) = (60) ( 87 + 60 )
As max = 0.6375 β1 (b) (d)
(7)
y
1.51 in2/ft
ok
Check Crack Control Requirements Calculate fs due to Service Load: M service load = 1.55 + 8.78 = 10.33 kip-ft/ft fs calc = M(12,000) / Asjd Where
j = l – k/3 = 0.884 Agrees with Table 1, page 81, ACI Publication SP-3 Reinforced Concrete Design Handbook Working Stress Design, 1965 k = 1 / 1 [ 1 + fs/nfc] = 1 / [ 1 + 24,000 / (8) (1,600) ] = 0.348 fs = 24,000 psi Grade 60 bars per AASHTO, Section 8.15.2.2 fc = 0.40 fc′ = 1,600 psi for Conc Cl 4000 n = Es / Ec = 29,000,000 / 3,620,000 = 8.0
fs calc = 10.33 (12,000) / (1.06) (0.884) (5.875) = 22,517 psi Using Eq (21), BDM Section 5.2.1G, Calculate allowable fs: fs allowable = z / [ (dc) (A) ]1/3 = 130 / [ (2.875) (5) (5.75) ]1/3 = 29.63 ksi > 22.52 ksi
5.2-B1-2
Eq (21) ok
July 2000
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Slab Design
Alternate Approach, Check zcalc < 130 kips/in using Eq (22): zcalc
= fs calc [ (dc) (A) ]1/3 < 130 kips/in = (22.52) [ (2.875) (5) (5.75) ]1/3 = 98.1 kips/in < 130 kips/in
Eq (22) ok
Use #6 bars at 5″ ctrs top and bottom transverse slab reinforcement.
Deck Reinforcement — Mid-Span Steel Plate Girder
July 2000
5.2-B1-3
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Slab Design for Prestressed Girders
Example 5.2-B2 Given: Center-to-center spacing of W58G girders Width of top flange Average flange thickness Girder concrete strength fc′ Deck concrete, Class 5000 fc′ Cover to top bars Cover to bottom bars Find: 1.
= = = = = = =
8 feet 0 inches 25 inches wide 6 inches 7,000 psi 5,000 psi 2.5 inches 1.0 inch
Deck thickness, deck reinforcement
Determine Deck Thickness Minimum slab thickness = 7.5″ no overlay, per BDM, Chapter 6. This thickness permits the use of #6 transverse and #5 longitudinal bars. Seff = clear span per AASHTO 3.24.1.2(a) Width of top flange/average flange thick = 4.16 Close enough to 4.0, use clear span for Seff Seff = Sg – W2 = 8.0′ – 2.083′ = 5.92′ Check Minimum Slab Thickness, tmin: tmin = (Seff + 10) (12) / 30 = (5.92′ + 10) (12) / 30 = 6.37″ < 7.5″
2.
ok
Determine Transverse Deck Reinforcement — Top Slab Reinforcement Dead Load Moment, MDL: MDL = (1/10) [ (7.5″ / 12) (0.160 kcf) ] (5.92)2 = 0.43 kip-ft/ft Live Load Moment + Impact, MLL+I: (S + 2) (6.54 + 2) (Pwheel) (0.8) (1.30) = (20.0) (0.8) (1.30) 32 32 = 5.15 kip-ft/ft
MLL+I = MLL+I
Factored Design Moment, Mu: Mu = 1.3 [ 0.35 + (5/3) (5.15) ] = 11.61 kip-ft/ft Determine As req’d: dtop bars = 7.5 – 2.5 – (0.75) / 2 = 4.625″ Mu / (φ) (b) (d)2 = 12.54 (12,000) / (0.9) (12) (4.625)2 = 651.4 psi Interpolating from Table 5.2-A3, Appendix A: ρ = 0.01089 As req’d = ρ (b) (d) = 0.01089 (12) (4.625) = 0.61 in2/ft Use #6 bars at 8″ ctrs, As = 0.66 in2/ft
ok
Use same bar size and spacing for bottom slab reinforcement.
July 2000
5.2-B2-1
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Slab Design for Prestressed Girders
3. Check Crack Control Requirements — Transverse Reinforcement Calculate fs due to Service Load: Mservice load = 0.35 + 5.15 = 5.50 kip-ft/ft fs calc = M (12,000) / Asjd where:
j = k = fc = Ec = fs = n =
l – k/3 = 1 – 0.375/3 = 0.875 1 / 1 [ 1 + fs/nfc ] = 1 / [ 1 + 24,000 / (7.2) (2,000) ] = 0.375 0.40 fc′ = (0.40) (5,000) = 2,000 psi for Concrete Class 5000 57,000 √ 5,000 = 4,030,500 psi 24,000 psi Grade 60 bars Es / Ec = 29,000,000 / 4,030,500 = 7.2
fs calc = 5.50 (12,000) / (0.66) (0.875) (4.625) = 24,710 psi top bar Calculate fs allowable = z / (Adc)1/3: A = (7.5″) (2.875″) (2) / 1 bar = 43.125
dc = 2.5 + 0.75 / 2 = 2.875″
fs allow = 130 / [ (43.125) (2.875) ]1/3 = 26.07 ksi > 24.71 ksi 4.
ok
Determine Longitudinal Deck Reinforcement Moments at Pier, Negative Reinforcement: MDL = 187.6 kip-ft/girder
MLL+I = 780.0 kip-ft/girder
Service Load Moments
Mu = 1.3 [ 187.6 + (5/3) (780.0) ] = 1,933.8 kip-ft/girder Determine As req’d assume two layers of #5 with davg = 64.0″: Mu / (φ) (b) (d)2 = 1,933.8 (12,000) / (0.9) (25) (64)2 = 251.8 psi Interpolating from Table 5.2-A3, Appendix A: ρ = 0.00433 As req’d = 0.00433 (25) (64.0) = 6.93 in2 Use 24-#5 (12-#5 in each layer) As = 7.44 in2 > 6.93 in2
ok
Spacing is approximately 8.0″, As/ft = 0.47 in2/ft Check longitudinal distribution reinforcement so that spacing can be coordinated with the reinforcement required for negative pier girder moment: P = 220 / √ S = 220 / √ 6.54 = 86.0 percent but not to exceed 67 percent Distribution Reinforcement = 0.67 (As actual) = 0.67 (0.70) = 0.47 in2/ft As provided = 0.47 in2/ft
5.2-B2-2
ok
July 2000
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Slab Design for Prestressed Girders
5. Check Crack Control Requirement — Longitudinal Reinforcement 24-#5
As = 7.44 in2
n = Es/Ec = 29,000,000 / 4,769,000 = 6.0
k =
√ 2 ρ n + (ρ n)2 – ρ n
k =
√ 2 (0.0047) (6.0) + [ (0.0047) (6.0) ]2 – (0.0047) (6.0) = 0.210
j = l – k/3 = 0.93 fs calc = M (12,000) / Asjd = 967.6 (12,000) / (7.44) (0.93) (64.0) = 26,220 psi fs allowable = z / [ (dc) (A) ]1/3 Use actual girder spacing = (8.0′) (12) = 96.0″ to compute A A = (96) (7.5) / 24 bars = 30.0 in2/bar fs allowable = 130 / [ 30.0 (3.56)
]1/3
dc = 2.5 + 0.75 + 0.625/2 = 3.56″
= 27.40 psi > 26.22 psi
ok
Deck Reinforcement at Intermediate Pier — Prestressed Girder Bridge Longitutdinal Deck Reinforcement is designed for the negative moment at an intermediate pier. Otherwise, the longitudinal deck reinforcement will be similar to that shown in Example 5.2-B1-1.
July 2000
5.2-B2-3
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Strut-and-Tie Design
Example 5.2-B3
Design Loads Group I: Pu = 1600k H=0 k Group VII: Pu = 1500 H = 400k Assume crossbeam dead load is included with bearing loads. Use Section 12.4 of AASHTO’s Guide Specifications for Design and Construction of Segmental Concrete Bridges, 1989.
July 2000
5.2-B3-1
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Strut-and-Tie Design
Develop a Preliminary Strut-and-Tie Model:
Estimate node size at top of column: φb (fcn Acn) ≥ Su Assuming spiral reinforcement provides confinement, use φb = 0.75 and fcn = 0.85 fc′: 0.75 (0.85 × 5) Acn ≥ 2,400 Acn ≥ 753 in2 Use the following node size at the top of column:
5.2-B3-2
July 2000
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Strut-and-Tie Design
Determine Truss Element Forces:
Group I Strut Loads
Group VII Strut Loads
Determine Minimum Size of Node Regions: φb (fcn Acn) ≥ Su
where: φb = 0.70 for bearing
fcn = 0.85 fc′ in regions with compression only fcn = 0.70 fc′ in regions with one tension tie At base of inclined strut, 0.75 (0.85 × 5) Acn ≥ 2,596 Acn ≥ 873 in2 depth of node =
873 = 12.1″ 72″
(72″ × 12.1″)
where width of crossbeam = 72″ 2,596 At top of inclined strut, Acn ≥ = 1,060 in2 0.70 (0.70 × 5) 1,060 depth of node = = 14.7″ (72″ × 14.7″) 72″ For 1,600k chord:
Acn ≥
1,600 = 538 in2 0.70 (0.85 × 5)
538 = 7.5″ 72″ 915 For 915k chord: Acn ≥ (538) = 308 in2 1,600 308 depth of node = = 4.3″ 72″ depth of node =
July 2000
5.2-B3-3
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Strut-and-Tie Design
Determine Minimum Sizes of Compression Members: φv (fcu Acs) ≥ Su
(inclined compressive struts)
φf (0.85 fc′ Acc + As′ fs′) ≥ Su
(compression chords)
For 2,596k inclined compressive strut: 0.85 (0.45 × 5) Acs ≥ 2,596k
(fcu = 0.45 fc′)
2,596 = 1,357 in2 0.85 (0.45) (5) 1,357 and depth of strut = = 18.9 in 72 Acs ≥
For 915k inclined compressive strut: 915 Acs ≥ (1,357) = 478 in2 2,596 478 and depth of strut = = 6.6 in 72 For 1,600k compression chord: Acs ≥
1,600 0.9 (0.85) (5)
and depth of chord =
= 418 in2 418 = 5.8 in 72
Incorporate Node and Member Sizes Into Model:
5.2-B3-4
July 2000
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Strut-and-Tie Design
Recalculate Truss Member Forces:
Group I Strut Loads
Group VII Strut Loads
Design Tie Member: φf (As fsy + A*s f*su) ≥ Su without prestress:
0.90 (As) (60) ≥ 2,240
As ≥ 41.5 in2 Try using 12 bundles of #14 top and #11 bot (As = 45.7 in2) Check development length of tie bars: For #14 bars with fc′ = 5,000 psi, ldh = 2′ – 5″ Development length available = 2′ – 4″ < 2′ – 5″ For #11 bars, ldh = 1′ – 5″
ok
Therefore, total developed steel As = 12 (1.56) + 12 (2.25) As = 44.8 in2 > 41.5 in2
( 2829 )
ok
Partial Elevation-Tension Tie at Top of Pier Cap 12 (2.25) (3.26) + 12 (1.56) (5.97) = 4.37″ = 4″ estimate x = ok 45.7
July 2000
5.2-B3-5
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Strut-and-Tie Design
Determine Minimum Vertical and Horizontal Steel Using Sections 12.5.3.2 and 12.5.3.3: For vertical reinforcing: As fy ≥ 120 bw s d where s < or 12″ 4 120 bw s Therefore, As ≥ = 0.002 bw s 60,000 Assume 4 legs of #6 stirrups: As = 1.76 in2 s ≤
1.76 As = 0.002 (72) 0.002 bw
s ≤ 12.2 in Check:
d 72 – 4.37 = = 16.9″ 4 4
Therefore, use 4 #6 legs at 12″ maximum spacing. For horizontal reinforcing: where s < d or 12″ 3
As fy ≥ 120 bw s
For s = 12″, As ≥ 0.002 (72) (12) = 1.73 in2 Try 2 #8 bars: s ≤
(2 – #9 bars)
As = 1.58 in2
1.58 = 11.0″ 0.002 (72)
Use #8 bars at 11″ maximum spacing on side faces. For bottom bars, use #6 at approximately 12″ (7 – #6 bars)
5.2-B3-6
July 2000
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
Working Stress Design
Example 5.2-B4 Service Load — Concrete Stresses and Constants
July 2000
5.2-B4-1
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
5.2-B4-2
Working Stress Design
July 2000
BRIDGE DESIGN MANUAL Appendix B Reinforced Concrete Superstructures
July 2000
Working Stress Design
5.2-B4-3
BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures
Contents Page
6.0 6.1 6.1.1
6.1.2
6.1.3
6.1.4
6.1.5
6.1.6
6.1.7 6.1.8 6.2 6.2.1 6.2.2 6.2.3
6.2.4
6.2.5 6.3 6.3.1
Prestressed Concrete Superstructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Allowable Stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Strength of Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Modulus of Elasticity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Creep Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Shrinkage Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prestressing Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Allowable Stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prestressing Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Anchorages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Instantaneous Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Time-dependent Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Contract Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Shop Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Connections (Joints) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deflection and Camber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Precast Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pre-Tensioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Post-Tensioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Washington Standard Prestressed Girder Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Section Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Basic Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Design Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Prestressing Strands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Development of Prestressing Strand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Fabrication and Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Precast Prestressed (Short Span Bridges) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Precast Prestressed Slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Precast Prestressed Tri-Beam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Precast Prestressed Deck Bulb-Tee Girders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Precast Box Girders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Precast Girder Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Criteria for Girder Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Support Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Composite Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Prestressed Girder Camber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
July 2000
6.1-1 1 1 1 1 1 1 2 2 3 3 3 3 3 3 3 3 4 4 5 5 5 5 5 6 6.2-1 1 1 1 1 1 3 4 7 8 10 14 14 14 15 15 6.3-1 1 1 1 7
6.0-i
BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures
Contents Page
6.3.2
6.3.3
6.3.4
6.3.5
6.3.6
6.4 6.4.1
6.4.2
6.4.3 6.99
6.0-ii
Framing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Girder Selection and Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Slab Cantilevers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Diaphragm Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Skew Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Grade and Cross Slope Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Curve Effect and Flare Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Simple Spans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Continuous Spans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Roadway Slab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Slab Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Transverse Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Crossbeam Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Geometry and Construction Requirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Skin Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Repair of Damaged Bridge Girders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Repair Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Miscellaneous References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cast-in-Place Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Bridge Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Section Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Strand and Tendon Arrangements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Layout of Anchorages and End Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Superstructure Shortening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Section Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Preliminary Stress Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Tendon Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Prestress Losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Steel Stress Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Prestress Moment Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Flexural Stress in Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Temperature Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. Shear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. End Block Stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . K. Anchorage Stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L. Camber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. Expansion Bearing Offsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. Post-Tensioning Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Review of Shop Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10 10 11 12 13 13 13 13 13 14 18 18 20 21 21 21 21 22 22 22 22 24 6.4-1 1 1 1 2 3 3 10 10 11 11 12 13 13 15 16 17 18 19 20 20 20 20 21 6.99-1
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BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures
Contents
Appendix A — Design Aids 6.1-A1 “A” Dimension for P.S. Concrete Bridges 6.2-A1 W95G and W83G 6.3-A1 Prestressed Girder Intermediate Hinge Diaphragm 6.4-A1-1 WSDOT Standard Girder — Composite Sections 6.4-A1-2 WSDOT Standard Girder — Non-Composite Sections 6.4-A2 WSDOT Standard Girders Section Properties — Composite Sections 6.4-A3-1 WSDOT Standard Girders Section Properties — Non-Composite Sections 1 of 2 6.4-A3-2 WSDOT Standard Girders Section Properties — Non-Composite Sections 2 of 2 6.4-A4 WSDOT Standard Girders Span Range Capacity 6.5-A1-1 W42G Girder Details 1 of 2 6.5-A1-2 W42G Girder Details 2 of 2 6.5-A2-1 W50G Girder Details 1 of 2 6.5-A2-2 W50G Girder Details 2 of 2 6.5-A3-1 W58G Girder Details 1 of 2 6.5-A3-2 W58G Girder Details 2 of 2 6.5-A4-1 W74G Girder Details 1 of 2 6.5-A4-2 W74G Girder Details 2 of 2 6.5-A5-1 WF74G Girder Details 1 of 3 6.5-A5-2 WF74G Girder Details 2 of 3 6.5-A5-3 WF74G Girder Details 3 of 3 6.5-A6-1 W83G Girder Details 1 of 3 6.5-A6-2 W83G Girder Details 2 of 3 6.5-A6-3 W83G Girder Details 3 of 3 6.5-A7-1 W95G Girder Details 1 of 3 6.5-A7-2 W95G Girder Details 2 of 3 6.5-A7-3 W95G Girder Details 3 of 3 6.5-A8 End Wall on P.S. Concrete Girder — Diaphragm Details 6.5-A9 Abutment Type Pier — Diaphragm Details 6.5-A10-1 Intermediate Pier — Fixed Recessed-Face Diaphragm Details 6.5-A10-2 Intermediate Pier — Fixed Flush-Face Diaphragm Details 6.5-A10-3 Intermediate Pier — Hinge Diaphragm Details 6.5-A10-4 Intermediate Pier — End Wall on Girder Details 6.5-A11 Intermediate Diaphragm Details 6.5-A12 Miscellaneous Diaphragm Details 6.5-A13 Single Span Prestressed Girder Construction Sequence 6.5-A14 Multiple Span Prestressed Girder Construction Sequence 6.6-A1-1 Precast Prestressed 1′-0″ Solid Slab Details 1 of 2 6.6-A1-2 Precast Prestressed 1′-0″ Solid Slab Details 2 of 2 6.6-A2-1 Precast Prestressed 1′-6″ Voided Slab Details 1 of 2 6.6-A2-2 Precast Prestressed 1′-6″ Voided Slab Details 2 of 2 6.6-A3-1 Precast Prestressed 2′-2″ Voided Slab Details 1 of 2 6.6-A3-2 Precast Prestressed 2′-2″ Voided Slab Details 2 of 2
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BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures 6.6-A4 6.6-A5 6.6-A6 6.7-A1-1 6.7-A1-2 6.7-A3 6.8-A1-1 6.8-A1-2 6.8-A1-3 6.8-A1-4 6.8-A2-1 6.8-A2-2 6.8-A2-3 6.8-A2-4 6.8-A3-1 6.8-A3-2 6.8-A3-3 6.8-A3-4 6.8-A4-1 6.8-A4-2 6.8-A4-3 6.8-A4-4 6.8-A5
Contents
Precast Prestressed Slab End Pier Details Precast Prestressed Slab Intermediate Pier Details Precast Prestressed Slab Layout Precast Prestressed Ribbed Tri-Beam Girder Details 1 of 2 Precast Prestressed Ribbed Tri-Beam Girder Details 2 of 2 Precast Prestressed Ribbed Tri-Beam Girder Pier Details W35DG Deck Bulb Tee Girder Details 1 of 2 W35DG Deck Bulb Tee Girder Details 2 of 2 W35DG Deck Bulb Tee Girder Design Tables W35DG Deck Bulb Tee Diaphragm Details W41DG Deck Bulb Tee Girder Details 1 of 2 W41DG Deck Bulb Tee Girder Details 2 of 2 W41DG Deck Bulb Tee Girder Design Tables W41DG Deck Bulb Tee Diaphragm Details W53DG Deck Bulb Tee Girder Details 1 of 2 W53DG Deck Bulb Tee Girder Details 2 of 2 W53DG Deck Bulb Tee Girder Design Tables W53DG Deck Bulb Tee Diaphragm Details W65DG Deck Bulb Tee Girder Details 1 of 2 W65DG Deck Bulb Tee Girder Details 2 of 2 W65DG Deck Bulb Tee Girder Design Tables W65DG Deck Bulb Tee Diaphragm Details Deck Bulb Tee Diaphragm Details
Appendix B — Design Examples 6.1-B1 Post-Tensioning Anchorages 6.2-B1 Notes to Designers Post-Tensioning 6.3-B1 P.T. Box Girder Bridges Single Span 6.3-B2 P.T. Box Girder Bridges Two Span 6.3-B3 P.T. Box Girder Bridges Multiple Span
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BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures 6.0
Prestressed Concrete Superstructures
6.1
General
General
WSDOT uses three types of prestressed concrete bridges. They are (1) prestressed precast concrete girder or slab bridges, (2) cast-in-place post-tensioned bridges, and (3) combination prestressed/post-tensioned bridges. WSDOT utilizes prestressed concrete in special structures such as segmental cast-in-place or precast construction. This section provides criteria for these structure types and provides general guidance for other designs using prestressed concrete.
6.1.1
Criteria A. General AASHTO specifications shall be used to design prestressed concrete bridges, except as modified in this section. Prestressed concrete bridges shall be designed using working stress design and checked for ultimate load capacity. Refer to portions of Chapter 5 for information relating to concrete reinforcement and design methods used for prestressed structures. B. Allowable Stresses AASHTO standard specifications list the allowable stresses to be used in design except as noted below. 1.
Concrete Stresses at Service Load Under working stress conditions, tensile stresses in the precompressed tensile zone shall be limited to zero. This prevents cracking of the concrete during service life of the structure and provides more allowance for overloads during the life of the bridge.
2.
Shear Capacity Shear in webs of prestressed bridges shall be in accordance with AASHTO specifications. Where additional guidance is needed, the latest ACI Code should be consulted. For special considerations used for design of Washington State standard prestressed girders, see Subsection 6.3.
6.1.2
Concrete Properties A. Strength of Concrete Pacific NW aggregates have consistently resulted in excellent concrete strengths, to as much as 10,000 psi in 28 days. The following strengths are normally used for design. 1.
Precast Girders Nominal 28-day concrete strength (fc′) for precast girders with a cast-in-place deck is 7,000 psi. Where higher strengths would eliminate a line of girders, this strength can be specified, preferably at 8,500 psi, to a maximum of 10,000 psi. The final strength of concrete shall be specified as required by design and shall be shown on the plans. The minimum concrete compressive strength at release (fci′) for each prestressed girder in a bridge is to be calculated and shown in the plans. For a 28-day concrete compressive strength of 7,000 psi, a concrete compressive strength (at release) of between 3,500 and 6,000 psi shall be specified. For high strength concrete, the compressive strength at release shall be limited to
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BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures
General
7,500 psi. Release strengths of up to 8,500 psi can be achieved with extended curing for special circumstances. The specified concrete strength at release should be rounded to the next highest 100 psi. 2.
Cast-in-Place Post-tensioned Bridges Since conditions for placing and curing concrete on cast-in-place bridges are not controlled, as they are for precast bridge sections, a lower figure is used for concrete strength. Normally, use class 4000 concrete for post-tensioned cast-in-place bridges. Where significant economy can be gained and structural requirements dictate, the structure could be designed for class 5000 concrete.
3.
Cast-in-Place Slabs Concrete class 4000D shall be used for all cast-in-place bridge decks unless otherwise approved by the Bridge Design Engineer.
B. Modulus of Elasticity The modulus of elasticity for concrete strength up to 10 ksi is normally 33w3/2 √ fc′, where w is the weight of concrete in lbs/ft3. Normal weight concretes used in Washington generally have weights close to 160 lbs/ft3. With this value, the modules of elasticity equation simplifies to E = 66,800 √fc′. C. Creep Rate The creep coefficient for standard conditions may be taken as follows: Standard conditions are relative humidity ≤40 percent and average thickness of section 6 inches. 1.
Cast-in-Place Girders For most designs, the creep coefficient for loading at 7 days for moist-cured concrete and 1-3 days for steam-cured concrete is: 22 . t0.60.6 Ct = 6 + fc ′ 10 + t The final deflection is a combination of the elastic deflection and the creep effect associated with given loads shown by the equation below. ∆ total = ∆ elastic (1+ Ct) For other factors affecting this equation, see Reference 6.99.2 and 6.99.4. Reference to 6.99.4 discusses methods for calculating creep effects.
2.
Standard Prestressed Girders The creep coefficient for standard prestressed girders may be taken as: 3.95 . Ct = Ln (t + 1) 6 + f c′ Ct = creep coefficient t = time in days fc′ = ultimate strength of concrete in ksi
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BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures
General
D. Shrinkage Rate To compute the variation of shrinkage with time, use the following equations: t (∑SH)t = x 0.51 x 10-3 For moist cured concrete after 7 days: 35 + t t (∑SH)t = x 0.56 x 10-3 For steam cured concrete after 1 to 3 days: 55 + t Where (∑SH)t is the shrinkage strain at any point in time. For corrections to the shrinkage rate values including correction for initial shrinkage, see Reference 6.99.4.
6.1.3
Prestressing Steel A. General Three types of high-tensile steel are used for producing prestress. They are: 1.
Strands: ASTM A 416 Grade 270, low relaxation or stress relieved.
2.
Bars: ASTM A 722 Grade 150, Type 2.
3.
Parallel wires: ASTM A 421 Grade 240.
All WSDOT designs are based on low relaxation strands using either 1/2″ or 0.6″ diameter strands. B. Allowable Stresses Allowable stresses for design are as listed in AASHTO specifications.
6.1.4
Prestressing Systems A. General There are numerous prestressing systems. Most systems combine a method of stressing the prestressing strands with a method of anchoring it to concrete. B. Anchorages WSDOT requires approval of all multi-strand and/or bar anchorages used in prestressed concrete bridges by testing or by a certified report, stating that the anchorage assembly will develop the yield strength of post-tensioning steel. Manufacturers whose anchorages have been approved are.
6.1.5
1.
V.S.L. Corporation
2.
Avar Construction System
3.
Dywidag Systems International
Losses AASHTO specifications outline the method of predicting prestress losses for usual prestressed concrete bridges which may be used in design except as noted below. The following sources of prestress loss can influence the effective stress in the strand.
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6.1-3
BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures
General
A. Instantaneous Losses 1.
Anchorage slippage. This slippage is assumed to be 1/4 inch for design purposes.
2.
Friction losses. These losses are due to intended cable curvature and unintended wobble coefficient. For strands against rigid galvanized metal duct these values are respectively µ = 0.20 and k = 0.0002. For strands against smooth polyethylene duct µ = 0.16 and k = 0.0002.
3.
Elastic shortening of concrete.
B. Time-dependent Losses 1.
Creep of concrete.
2.
Shrinkage of concrete.
3.
Steel relaxation.
For normal design in lieu of more accurate methods, time dependent losses may be taken as given in Table 6.1.5-1. Type of Section
Low-relaxation Strands
Bars
Rectangular Beam
33 ksi
25 ksi
Box Girder
21 ksi
15 ksi
I-Girder
33 [1- 0.15 (fc′ - 6) / 6 ]
19 ksi
Single/Double T, Hollow Core Voided Slab
37 [ 1- 0.15 (fc′ - 6) / 6 ]
29 [ 1- 0.15 (fc′ - 6) / 6 ]
Time Dependent Prestress Losses Table 6.1.5-1 Prestress losses due to instantaneous sources shall be added to the time dependent losses to determine the total losses. The loss due to elastic shortening in pretensioned members shall be taken as: PLES = (Ep / Eci ) fcgp The loss due to elastic shortening in post-tensioned members shall be taken as: PLES = [(N-1)/2N x Ep / Eci ] fcgp where: Ep = modulus of elasticity of prestressing steel, ksi Eci = modulus of elasticity of concrete at transfer, ksi N
= number of identical prestressing tendons
fcgp = sum of concrete stresses at the center of gravity of prestressing tendons due to the prestressing force at transfer (after jacking for posttensioned members) and the self-weight of the member at the section of maximum moment, ksi For pretensioned member and low-relaxation strands, fcgp may be calculated on the basis of 0.7fpu. For post-tensioned members with bonded tendons, fcgp may be calculated on the basis of prestressing force after jacking at the section of maximum moment. For preliminary design of pretensioned prestressed girders with normal strength concrete limited to 7,000 psi, the total prestress loss may be taken as 48 ksi.
6.1-4
July 2000
BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures 6.1.6
General
Construction A. General Construction plans for conventional post-tensioned box girder bridges include two different sets of drawings. The first set (contract) is prepared by the design engineer (WSDOT or contracting agency) and the second set (shop) is prepared by the post-tensioning materials supplier (contractor). B. Contract Plans The plans should be prepared to accommodate any post-tensioning system, so only prestressing forces and eccentricity should be detailed. The concrete sections should be detailed so that available systems can be installed. Design the thickness of webs and flanges to facilitate concrete placement. Generally, web thickness for post-tensioned bridges shall be at least 12 inches. C. Shop Plans The shop plans are used to detail, install, and stress the post-tensioning system selected by the Contractor. These plans must contain sufficient information to allow the engineer to check their compliance with the contract plans. These plans must also contain the location of anchorages, stressing data, and arrangement of tendons.
6.1.7
Connections (Joints) The connections or joints must divide the structure into a logical pattern of separate elements which also permit ease of manufacture and assembly. The connection or joint surfaces should be oriented perpendicular to the centroidal axis of the precast element. Types of Connections (Joints): Connections or joints are either wide or match cast. Depending on their width, they may be filled with cast-in-place concrete or grouted. Match cast joints are normally bonded with an epoxy bonding agent. Dry match cast joints are not recommended. Shear and Alignment Keys: In order to assist shear transmission in wide joints, use a suitable system of keys. The shape of the keys may be chosen to suit a particular application and they can be either single keys or multiple keys. Single keys are generally large and localized whereas multiple keys generally cover as much of the joint surface area as is practical.
Single Key
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Multiple Keys
6.1-5
BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures
General
Single keys provide an excellent guide for erection of elements. Single keys are preferred for all match cast joints. For all types of joints, the surfaces must be clean, free from grease and oil, etc. When using epoxy for bonding, the joints should be lightly sand-blasted to remove laitance. For cast-in-place or other types of wide joints, the adjacent concrete surfaces should be roughened and kept thoroughly wet, prior to construction of the joint. Cast-in-place joints are generally preferred.
6.1.8
Deflection and Camber Deflections of prestressed concrete beams can be predicted with greater accuracy than those for reinforced concrete beams. Since prestressed concrete is more or less homogeneous and obeys ordinary laws of flexure and shear, the deflection can be computed using elementary methods. However, accurate predictions of the deflections are difficult to determine, since modulus of elasticity of concrete, Ec, varies with stress and age of concrete. Also, the effects of creep on deflections are difficult to estimate. For practical purposes, an accuracy of 10 to 20 percent is often sufficient. Prestressing can be used advantageously to control deflections, however, there are cases where excessive camber due to prestress have caused problems. For normal design, in lieu of more accurate methods, the deflection and camber of prestressed members may be estimated by the multipliers as given in Table 6.1.8-1. Multipliers for Estimating Long-term Deflection of Prestressed Concrete Girders Table 6.1.8-1 Normal Strength Concrete fc′ 7.0 ksi
NonComposite
Composite
NonComposite
Composite
Apply to the elastic deflection due to the member weight at release of prestress
1.85
1.85
1.75
1.75
Apply to the elastic deflection due to prestressing at release of prestress
1.80
1.80
1.70
1.70
Apply to the elastic deflection due to the member weight at release of prestress
2.70
2.40
2.50
2.20
Apply to the elastic deflection due to prestressing at release of prestress
2.45
2.20
2.25
2.10
Apply to the elastic deflection due to the Super Imposed Dead Loads
3.00
3.00
2.75
2.75
----
2.30
----
2.15
Deflection at Erection
Deflection at Final
Apply to the elastic deflection due to weight of slab release of prestress
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BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures 6.2
Precast Sections
Precast Sections Precast sections are generally cast in a permanent plant or somewhere near the construction site and then erected. Precasting permits better material quality control and is often more economical than cast-in-place concrete. The precast ‘U’ sections are commonly called ‘bathtubs’ which can be joined together with “wet joint.”
6.2.1
Pre-Tensioning Pre-tensioning is accomplished by stressing high strength steel strands to a predetermined tension and then placing concrete around the strands, while the stress is maintained. After the concrete has hardened, the strands are released and the concrete, which has become bonded to the tendon, is prestressed as a result of the strands attempting to relax to their original length. The strand stress is maintained during placing and curing of the concrete by anchoring the ends of strands to abutments that may be as much as 500 feet apart. The abutments and appurtenances used in this procedure are referred to as pre-tensioning bed or bench.
6.2.2
Post-Tensioning Post-tensioning consists of installing steel tendons into a hollow metalic duct in a structure after the concrete sections are cast. These tendons are usually anchored at each end of the structure and stressed to a design strength using a hydraulic jacking system. Commonly the tendons are encased in a tight metal tube. This tube is referred to as a sheath or duct and remains in the structure. After the tendon has been stressed, the duct is filled with grout which bonds the tendon to the concrete section and prevents corrosion of the strand. Finally, closure pours are made at the anchor heads to provide corrosion protection.
6.2.3
Washington Standard Prestressed Girder Sections Washington State Standard girders were adopted in the mid-1950s. These girder shapes proved to be very efficient due to their thin webs and small flange fillets. These are still the most efficient shapes available and variations of these girders have been adopted by other states. The original series was graduated in 10-foot increments from 30 feet to 100 feet. In 1990, revisions were made to the prestressed concrete girder standards incorporating the results of the research done at Washington State University on girders without end blocks. The new standards incorporate three major changes. They have a thicker web, the end blocks are eliminated, and have increased distance between strands. The new standard designations are W74G, W58G, W50G, W42G, and deck bulb tee standards W53DG and W35DG. The numbers refer to the depth of the section. In 1999, deeper girders, commonly called “Supergirders” were added to the WSDOT prestressed concrete girder standards. These new supergirders may be pretensioned or post-tensioned. The pretensioned standards are designated as WF74G, W83G and W95G and the post-tensioned standards are designated as W83PTG and W95PTG. A. Properties The properties which are needed for design of standard girders are listed in Appendix 6.4-A3-1 and 2. B. Section Geometry Table 6.2.3-1 gives the dimensions of the Washington State Standard Girder Sections.
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6.2-1
BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures
Precast Sections
Dimensions of Standard Prestressed Girder Sections Table 6.2.3-1
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BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures
Precast Sections
C. Basic Assumptions The following basic assumptions are used in the design of these standard girders. Figure 6.2.3-1 illustrates some of the factors which are constant in the WSDOT Prestressed Girder Design computer program. Figure 6.2.3-2 show variations from those assumptions for a typical backwall design and a typical notched girder design.
Typical Prestressed Girder Span Figure 6.2.3-1
Typical Prestressed Girder Configuration Figure 6.2.3-2 Figure 6.2.3-3 and Appendix 6.5-A1 through A7 show the standard strand positions in these girders.
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6.2-3
BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures 1.
Precast Sections
Prestress For final conditions, the designer shall assume the prestress acting on the section to be NAs (.70 fs′-PL) for stress relieved strands and NAs (.75 fs′-PL) for low relaxation strands. Where: N
= number of stressed strands passing through the section
As = the area of one strand, in2 fs′ = the ultimate strength in ksi PL = indicates total prestress losses in ksi in pretensioned members. For checking of stresses during release, lifting, transportation, and erection of prestressed girders, the elastic and time dependent losses shall be as follows: Release — 1 day (lifting of girders from casting beds) 1 month — 4 months (transportation and erection of girders) After 4 months 2.
computed losses 35 ksi computed losses
Strand Patterns Standard strand patterns are shown in Appendix 6.5-A1 through A7.
D. Design Procedure 1.
General The WSDOT “Prestressed Girder Design” computer program uses a trial and error method to arrive at solution for stress requirement and is the preferred method for final design of length and spacing. Some publications suggest various direct means for determining stress and position, but the procedures are generally quite complex.
2.
Stress Conditions The stress limits as described in Table 6.2.3-2 must be met for the girder and its prestress. One or more of the conditions described below may govern design. Each condition is the result of the summation of stresses with each load acting on its appropriate section (such as girder only, composite section). Precast girders shall also be checked during lifting, transportation, and erection stages by the designer to assure that girder delivery is feasible. Impact during the lifting stage shall be 0 percent and during transportation shall be 20 percent of the dead load of the girder. Impact shall be applied either upward or downward to produce maximum stresses.
6.2-4
July 2000
BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures
Precast Sections
Prestressed Girder Strand Locations Figure 6.2.3-3 Note:
Fo may be increased in 1-inch increments to keep slope of harped strands below the slope limit. Fb may be increased in 1-inch increments in order to reduce tension at the top of the girder at harping point at time of strand release.
July 2000
6.2-5
BRIDGE DESIGN MANUAL Criteria Prestressed Concrete Superstructures
Precast Sections
Condition
Stress
Location
Temporary Stress at Transfer
Tensile
In areas other than Precompressed Tensile Zone
3 √fci′ Gmin = 7.50" ok Total Opening = 10.375 + (7.7)(1.15) = 19.23" < Gmax = 19.50" ok Check spacing between centerbeams at minimum temperature: G at 0°F = 10.375 + 7.7 = 18.075" < Gmax Maximum spacing = [18.075 - 3(2.5)]/4 seals = 2.643" < 31/2" ok b.
D. S. Brown Co.,Type D-321, MR =12" Gmin = 3(2.213) + 4(0.5) = 8.64" Gmax = 8.75 + 12 = 20.75"
Use 83/4" Use 203/4"
Construction Width at 64°F: G at 64°F = Gmin + Closing Movement Due to Temperature Rise = 8.75 + (2.40)(1.15) = 11.51"
Use 115/8"
By comparison to previous calculations for Watson Bowman ACME, the construction width calculations for the D. S. Brown Co.’s, Type D-321, will be 11/4" greater (11.625" = 10.375") than those computed for the Watson Bowman ACME, WABO D-1200. Construction Width at 40°F: G = 131/4" Construction Width at 80°F: G = 105/8" Check if G at 64°F is 115/8" (include 15 percent safety factor): Total Closing = 11.625 - (2.4)(1.15) = 8.86" > Gmin = 83/4" ok Total Opening = 11.625 + (7.7)(1.15) = 20.48" < Gmax = 203/4" ok Check spacing between centerbeams at minimum temperature: G at 0°F = 11.625 + 7.7 = 19.325" Max. spacing = [19.325 - 3(2.213)]/4 seals = 3.17" < 31/2" ok
8-4-B8:V:BDM8
8.4 - B8 - 2
September 1992
BRIDGE DESIGN MANUAL Appendix B Miscellaneous Design
Reinforced Elastomeric Bearing Pad Design Example for Prestressed Girder (AASHTO Design Method A)
Standard WSDOT W74G simple span prestressed concrete girder bridge. Span length is 130 feet. Bottom flange width of the girder is 25 inches. Use a temperature range of 0°F to 100°F for concrete bridges with a normal construction temperature of 64°F. Use AASHTO Standard Specifications Section 14.4.1 Design Method A. Bearings shall be installed so that they are horizontal (level) under dead load. Loading: Dead Load reaction per bearing: PDL, Girder = 108 kips PDL, Slab+Traffic Barrier = 112 kips Live Load reaction per bearing (excluding impact): PLL,HS25 = 60 kips Live Load rotation (calculated from analysis) θLL,x = Live load rotation (excluding impact) = 0.003 radians (from structural analysis) Constants: α = Coefficient of thermal expansion for concrete = 0.000006/°F β = Shrinkage coefficient for reinforced concrete = 0.0002 in/in µ = Shrinkage factor = 0.5 BDM Section 8.4.1A.1.b.(1) Elastomer Design Parameters: Durometer Hardness = 60 From AASHTO Table 14.3.1, for a 60 durometer hardness elastomer, the shear modulus varies between 0.130 ksi and 0.200 ksi. Use a value corresponding to the most conservative design. Internal Steel Reinforcement: 14 gauge plate (thickness = 0.075") Fy = 36 ksi Fsr = 20 ksi The bearing design shall conform to the following additional WSDOT standard requirements: (a) Design for a 60-durometer elastomer. (b) Unreinforced (plain) pads shall not be used. (c) Internal elastomer layers shall be 1/2 inches thick; external elastomer layers shall be 1/4 inches thick. (d) Minimum number of internal elastomer layers shall be two. (e) Maximum overall height of the bearing shall not exceed 5 inches. (f) Tapered elastomer layers shall not be used. (g) The shape factor of each layer of any reinforced bearing shall be equal to or greater than 5.0.
August 1998
8.4-B9-1
BRIDGE DESIGN MANUAL Appendix B Reinforced Elastomeric Bearing Pad Design Example for Prestressed Girder (AASHTO Design Method A)
Miscellaneous Design
(h) The average compressive stress from dead load and uplift, if any, shall not be less than 200 psi to avoid “walking” of the bearings. (i) Design loading shall take into account the effect of skew and curvature. (j) The bearing design movement shall be based upon 75 percent of the total calculated temperature rise and fall using an assumed normal temperature of 64°F plus any other anticipated movements or translations. (k) Girders are placed on the elastomeric bearing pads 30 days following casting. The remaining creep of the girders tributary to each bearing has been calculated to be 0.20". (l) The design details shall provide access for inspection, maintenance, and future replacement of each bearing. (m) For thick bearings, calculate the grout pad elevations using the compressed height of the bearing. 1.
Determine preliminary bearing size Temperature fall (64° → 0°F):
(0.000006)(64) (65)(12)
= 0.30″
Temperature rise (64° → 100°F):
(0.000006)(36)(65)(12)
= 0.17″
(0.5)(0.0002)(65)(12)
= 0.08″
Shrinkage: Creep (calculated from girder age of 30 days to infinity):
= 0.20″
∆s = 0.75 (Dfall + Drise)+ Dshrink +Dcreep = 0.75(0.30 + 0.17) + 0.08 + 0.20 = 0.63″ Determine bearing thickness: Minimum total elastomer thickness ≥ 2∆s hrt ≥ (2)(0.63″) = 1.26″
(AASHTO Section 14.4.1.3)
Minimum total elastomer thickness required
Use (2) - 1/2″ thick interior layers of elastomer and 1/4″ thick cover layers. 2 interior layers at 1/2″ 2 cover layers at 1/4″ Total elastomer thickness, hrt
= = =
1.0″ 0.5″ 1.5″ > 1.26″
ok
Use (3) - 14 gage steel shims. Sum of shim thicknesses = (3)(0.075″) = 0.225″ Total bearing thickness = T = 1.50″ + 0.225″ = 1.725″ < 5″ maximum
ok
Determine bearing width, W: Use a width equal to the width of the prestressed concrete girder bottom flange less two 1″ chamfers less an additional 1/2″ on each side. W = 25 in - 2(1″) - 2(0.5″) = 22″
Use W = 22″
Determine bearing length, L: σc,TL ≤ 1.000 ksi for steel reinforced bearings
(AASHTO 14.4.1.1)
(220 kips + 60 kips) ∏ [(L)(22)] £ 1.000 ksi L ≥ 12.73″
Use L = 13″
Preliminary bearing size: 13″ wide ξ 22″ long × 1.725″ thick
8.4-B9-2
August 1998
BRIDGE DESIGN MANUAL Appendix B Miscellaneous Design 2.
Reinforced Elastomeric Bearing Pad Design Example for Prestressed Girder (AASHTO Design Method A)
Check allowable compressive stress Determine the Shape Factor, S, of the 1/2″ thick interior layers: S = (L)(W) ∏ [2(hri)(L + W)]
(AASHTO 14.2)
= (13)(22) ∏ [(2)(0.50)(13 + 22)] = 8.17 > 5.0 minimum σc,TL,allowable= GS/b = (.130)(8.17)/1.0 = 1.062 ksi, but not greater than 1.000 ksi 14.4.1.1) σc,TL= 280 kips ÷ [(13)(22)] = 0.979 ksi £ 1.000 ksi
(AASHTO
ok
Check compressive stress under minimum load only. Keep σc,DL > 0.200 ksi to keep bearing from “walking” under minimum load. Assume minimum load occurs under dead load and uplift, if any. σc,DL= 220 kips ∏ [(13)(22)] = 0.769 ksi ≥ 0.200 ksi 3.
ok
Check bearing stability (AASHTO 14.4.1.5) To ensure stability, the total thickness of the bearing should not exceed the lesser of W/3 or L/3. W/3 = 22″/3 = 7.33″ > 1.725″ L/3 = 13″/3 = 4.33″ > 1.725″
4.
ok ok
Check steel reinforcement (AASHTO 14.4.1.6) Resistance of internal elastomer layer = 1,700hri = 1,700(0.5≤) = 850 lbs/inch Pallow = (Fsr)(hs) = (20000 psi)(0.075≤) = 1500 lbs/inch > 850 lbs/inch
5.
ok
Check if bearing needs to be secured against horizontal movement (AASHTO 14.5): Determine the design shear force on bearing, H: H = GA∆s /hrt = (0.200)(13)(22)(0.63) ÷ (1.5) = 24.0 kips PDL / 5 = 220 / 5 = 44.0 > 24.0 kips → Anchorage of the bearing is not required.
6.
Check rotation (AASHTO 14.4.1.4) Rotation perpendicular to the beam’s longitudinal axis: θTL,x ≤ 2∆c/ L Rotation parallel to the beam’s longitudinal axis:
θTL,z ≤ 2∆c/ W
Determine the compressive deflection, ∆c, using AASHTO Figure 14.4.1.2B: Compressive stress = 0.979 ksi and Shape factor = 8.17 → Compressive strain = 0.039 ∆c = (.039)[2(0.5″) + 2(0.25″)] = 0.058″ Assume girders are level after placement of slab and traffic barriers. Therefore, θTL,x = θLL,x = 0.003 radians and θTL,z= 0.000 radians. qTL,x, allowable = 2∆c / L qTL,x,allowable= 2(0.058)/13 = 0.0090 radians > 0.003 radians
August 1998
ok
8.4-B9-3
BRIDGE DESIGN MANUAL Appendix B Reinforced Elastomeric Bearing Pad Design Example for Prestressed Girder (AASHTO Design Method A)
Miscellaneous Design Summary: Size:
Length = 13″
Width = 22″
Overall total thickness = 1.725″
Elastomer layers:
2 interior layers at 1/2″ thick 2 cover layers at 1/4″ thick Total Thickness = 1.725"
Steel reinforcement:
3 steel shims, 14 gage (0.075 inch thickness) Provide 1/8″ minimum side clearance for the steel shims
P:DP/BDM8 9807-0802
8.4-B9-4
August 1998
BRIDGE DESIGN MANUAL Appendix B Miscellaneous Design
July 1996
Elastomeric Bearing Pad Example for Steel Girder
8.4 - B11
BRIDGE DESIGN MANUAL Appendix B Miscellaneous Design
Girder Stop Bearing Pads Example
Spacing Chart: Page 8.4-B14 Pad Thickness Chart: Page 8.4-B15 Known:
Skew = 33° Girder = Series 120 Spacing = 8′-0″ (Normal to Girder)
From Spacing Chart (F(Ep)T ≅ 7,500 Lbs. > 22,200 Lbs. ∴ Pad Required Known:
Bridge Length = 420″ (Bk-Bk. Pavement Seat)
From Pad Thickness Chart:
T = 2.32″ Use T = 21/2″ (1/2″ Laminates)
Girder Stop Bearing Pad Dimensions Thickness = 21/2″ Length = 3 × 2.5 = 71/2″ Width = 5″ (Flange Depth - Chamfer) (Number of Pads Required): Pad Thickness = 31/2″
Known:
F(Ep)T = 7,500 Lbs. (From Spacing Chart) Number of Girders = 6 From Pad Thickness Chart:
2.4 Pads Required
Use Girder Stop Bearing Pads on three (3) of the girders in each end span. Place pads on proper side of girder to oppose lateral component of force from earth pressure.
August 1998
8.4-B12-1
BRIDGE DESIGN MANUAL Appendix B Miscellaneous Design
8.4-B12-2
Girder Stop Bearing Pads Example
July 1996
BRIDGE DESIGN MANUAL Appendix B Miscellaneous Design
July 1996
Elastomeric Bearing Pad Design Chart
8.4 - B13
BRIDGE DESIGN MANUAL Appendix B Miscellaneous Design
July 1996
Girder Stop Bearing Pads Spacing Chart
8.4 - B14
BRIDGE DESIGN MANUAL Appendix B Miscellaneous Design
July 1996
Girder Stop Bearing Pads Pad Thickness Chart
8.4 - B15
BRIDGE DESIGN MANUAL Criteria Substructure Design
Contents Page
9. 9.1 9.1.1
9.1.2 9.1.3
9.2 9.2.1
9.2.2
9.3 9.3.1
9.3.2
Substructure Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Dead Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Wind Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Earthquake Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Prestressing Effects from Superstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Design for Substructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Application of Loads to Substructure Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Earthquake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Piers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Spacing of Piers and Columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Section Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Construction Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Column Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Column Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Column Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Slenderness Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. The Moment Magnification Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Second-Order Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Resisting Capacities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Service Load Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Seismic Design of Multicolumn Bents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Abutments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Size and Construction Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Representative Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Bearing Seats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Bearing Restraints and Girder Stops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Face Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Sizing Abutments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Class of Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Abutment and Retaining Wall Junctions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Construction Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. Drainage and Backfilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Embankment at Bridge Ends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Abutment Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Applicable Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Usual Governing Load Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Special Handling of Lateral Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Loads on Girder Stop Bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Loads on Girder Stops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
July 2000
9.1-1 1 1 1 1 1 3 3 3 4 4 4 4 9.2-1 1 1 1 1 2 4 11 11 11 15 17 20 21 21 9.3-1 1 1 1 1 1 1 1 4 4 4 6 12 12 16 16 19 19
9.0-i
BRIDGE DESIGN MANUAL Criteria Substructure Design
Contents Page
9.3.3
9.3.4
9.4 9.4.1 9.4.2
9.4.3
9.4.4
9.5 9.5.1
9.5.2
9.0-ii
General Design Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Design for Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Earth Pressure at Front Face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Design for Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Minimum Reinforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load and Reinforcement Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Requirements for Pile Cap Abutments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Requirements for Pile Stub Abutments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Requirements for Cantilever Abutments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Requirements for Spill-Through Abutments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Requirements for Rigid Frame Abutments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Retaining Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Common Types of Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Cantilevered Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Counterfort Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Gravity Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Cribbing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Cylinder Pile Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Tieback Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Proprietary Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Slurry Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. Rock Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Soil Nailing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . K. Wingwall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L. Noise Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Cantilever Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Diaphragm Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Tieback Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Miscellaneous Items . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Architectural Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Concrete Fill for Soldier Pile Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Detailing of Standard Reinforced Concrete Retaining Walls . . . . . . . . . . . . . . . . . . . . . . . . . . Footings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spread Footings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Load Distribution Under Footings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Pedestals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Footing Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pile Supported Footings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Pile Spacings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Horizontal Forces on Pile Groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Uplift Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3-19 19 19 19 19 20 20 20 23 23 23 9.4-1 1 1 1 1 1 1 2 2 2 4 4 4 4 4 4 4 9 10 14 29 29 29 29 30 30 9.5-1 1 1 5 5 6 9 9 9 10 10
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9.6 9.6.1
9.6.2
9.6.3
9.6.4 9.6.5 9.6.6 9.6.7 9.7 9.7.1 9.7.2
9.7.3
9.7.4 9.8 9.8.1
9.8.2
9.8.3
9.8.4
Piles and Piling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Selection of Pile Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Friction vs. Point Bearing Piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Pile Loads and Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Column Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Uplift Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Lateral Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Other Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Concrete Pile Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steel Piling (H Piles) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Timber Piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sheet Piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cylinder Piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Normal High Water Elevation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Seal Vent Elevation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Scour Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Recommended Foundation Elevation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spread Footings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Seal Positively Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Seal May Not Be Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pile Supported Footings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drilled Shafts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types of Drilled Shafts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Classification by Load Transfer to the Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Classification by Type of Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Advantages and Disadvantages of the Drilled Shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preliminary Soils Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Surface Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Subsurface Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Methods of Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Subsurface Conditions Affecting Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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9.6-1 1 1 1 1 2 2 3 4 4 6 6 6 7 7 7 7 9.7-1 1 1 1 2 2 2 2 2 3 3 9.8-1 1 1 1 1 1 1 1 2 2 2 3 3 3 3 3
9.0-iii
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9.8.5
9.8.6
9.8.7
9.9 9.9.1 9.9.2 9.9.3 9.9.4
9.9.5
9.9.6 9.9.7
9.9.8
9.99
9.0-iv
Design of Drilled Shafts for Axial Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Ultimate Failure vs. Excessive Settlement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Factor of Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Spacing, Depth, Diameter Reinforcing, and Concrete Strength of Drilled Shafts . . . . . . . . . . Design of Drilled Shafts Subject to Lateral Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General Modeling Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. P-Y Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Analysis by Computer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Shaft Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Construction Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Dry Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Casing Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Slurry Displacement Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Application of LRFD Code to WSDOT Foundation Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Overall Design Process, Roles, and Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Definitions and Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LRFD Load Combinations, Basic Equation, and Characteristic Soil/Rock Projects . . . . . . . . . . . . A. LRFD Basic Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Characteristic Soil/Rock Properties and Their Use in LRFD . . . . . . . . . . . . . . . . . . . . . . . . . . Spread Footing Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Loads and Load Factor Application to Spread Footings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Footing Bearing Stress and Capacity — Strength and Extreme Event Limit States . . . . . . . . . C. Sliding Stability for Footings — Strength and Extreme Event Limit States . . . . . . . . . . . . . . . D. Overturning Stability for Footings — Strength and Extreme Event Limit States . . . . . . . . . . . E. Overall Stability for Footings — Service and Extreme Event Limit States . . . . . . . . . . . . . . . F. Resistance Factors for Footing Design — Strength Limit State . . . . . . . . . . . . . . . . . . . . . . . . G. Design of Footings at the Service Limit State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. What the Geotechnical Branch Will Provide to the Bridge Office for LRFD Footing Design Loads and Load Factor Application to Deep Foundation Design . . . . . . . . . . . . . . . . . . . . . . . . . . . Drilled Shaft Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Drilled Shaft Capacity — Strength and Extreme Event Limit States . . . . . . . . . . . . . . . . . . . . B. Uplift for Drilled Shafts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Lateral Load Analysis for Drilled Shafts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Group Effects for Bearing Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Group Effects for Uplift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Group Effects for Lateral Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Service Limit State Design for Drilled Shafts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. What Geotechnical Branch Will Provide to Bridge Office for LRFD Shaft Design . . . . . . . . Pile Foundation Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Pile Type, Pile Size, Bearing Capacity, and Estimated Tip Elevation — Strength and Extreme Event Limit States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Determination of Minimum Pile Tip Elevations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Resistance Factors for Pile Foundation Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Determination of Pile Driveability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. What Geotechnical Branch Will Provide to Bridge Office for LRFD Pile Design . . . . . . . . . . Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 4 4 5 9.8-6 6 7 8 9 9 9 9 9 9.9-1 1 4 5 7 7 7 9 10 13 14 15 15 16 17 17 19 22 23 24 24 24 26 26 28 28 31 33 37 38 39 39 9.99-1
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Contents
Appendix A — Design Aids 9.2-A1 24-Inch Diameter Round Column Section Capacity Chart 9.2-A2 36-Inch Diameter Round Column Section Capacity Chart 9.2-A3 48-Inch Diameter Round Column Section Capacity Chart 9.2-A4 60-Inch Diameter Round Column Section Capacity Chart 9.2-A5 72-Inch Diameter Round Column Section Capacity Chart 9.2-A6 Column Design Flow Chart 9.2-A7 Column Design Effective Length Factors 9.2-A8 Buckling Load — Round Columns 9.2-A9 Factor Charts 9.2-A10 Moment Magnification Factor 9.2-A11 Column Design Example 9.3-A1 Wing Wall Notes to Designers 9.3-A2 General Wing Wall Details (applies to 9.3-A1, A-3, A-4, and A-5) 9.3-A3 20-Foot Wing Wall 2:1 Slope 9.3-A4 15-Foot Wing Wall 2:1 9.3-A5 15-Foot Wing Wall 1 3/4:1 Slope 9.4-A1 Earthquake Force — Retaining Wall 9.5-A1 Stress on a Rectangular Footing Normal Load Outside Kern 9.7-A1 Thickness of Foundation Seals 9.7-A2 Pile Extension Below Foundation Seals 9.9-A1-1 through 5 Simplified Example for Pile Foundation Design, Including Resistance Factor Calibration Appendix B — Design Examples 9.2-B1-1 through 4 Column Shear Example 9.3-B1-1 through 5 L-Abutment Design Example — Sheet 1 9.4-B1-1 through 8 Curtain Wall
P65:DP/BDM9
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BRIDGE DESIGN MANUAL Criteria Substructure Design 9.1
General Considerations
9.1.1
Loads
General Considerations
A. General 1.
Substructure elements shall be designed to carry all of the loads specified in AASHTO, the Guide Specifications for Seismic Design of Highway Bridges and Chapter 4 of this manual. Good judgment is needed to select those load conditions which govern in order to minimize calculation time. Computer programs such as GPLOAD, GROUPLDS, and YIELD tabulate the load combinations as described in Chapter 4 of this manual.
2.
Consideration shall be given during design to construction loads in order to ensure that stability and appropriate stresses can be handled during all construction conditions. For example, a single column pier could be overloaded by placing all of the precast girders on one side of the roadway before placing those on the other side. In some cases a sequence of construction is shown on the plans in order to avoid unacceptable loadings.
3.
On curved bridges, the substructure units shall be designed for the eccentricity resulting from the differences in girder lengths. Where curved girder theory has been used in design of the superstructure, the reactions from such analysis shall be used appropriately as loads to the substructure.
B. Dead Loads Substructures shall be designed for all anticipated dead load conditions. Sidesway effect shall be included where it tends to increase stresses. C. Live Loads Live load shall be distributed to the substructure by placing the appropriate live load wheel line reaction in the lane configuration giving maximum stresses in the substructure unit. Liveload impact is not included in some elements of the substructure. See AASHTO “Impact.” The loads are considered to act directly on the substructure without further distribution through the superstructure except as previously noted. No consideration is given to torsional or lateral distribution. (See Figure 9.1.1-1.) Normally, sidesway effect from live load need not be considered. The computer program GTSTRUDL will include this effect. For maximum cantilever moment on the substructure units, the outside vehicle wheel shall be placed 2 feet from the curb. For the design loads in the crossbeam members, the design lanes are to be loaded to obtain the maximum moment in the member, then loaded again to obtain the maximum shear in the member. For the design loads in columns, the design lanes are to be loaded to obtain the maximum transverse moment at the top of the column, then loaded again to obtain the maximum axial force on the column. In each case, the lane reduction factor as described in AASHTO Article “Reduction in Load Intensity” can be applied to the number of lanes actually loaded to obtain the design loads. The live load wheel line reaction can be obtained by the computer programs BDS or UCONBRG. The wheel line reaction will be 1/2 the results for one lane load from BDS or the results for one wheel load from UCONBRG. For simple span structures, Appendix A of AASHTO can be used. The values in Appendix A are for one lane. The wheel line reaction will be 1/2 of the values listed.
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BRIDGE DESIGN MANUAL Criteria Substructure Design
9.1 - 2
General Considerations
BRIDGE DESIGN MANUAL Criteria Substructure Design
General Considerations
D. Wind Loads Wind forces shall be applied to the substructure units in accordance with the loadings specified in AASHTO Article “Wind Loads.” Transverse stiffness of the superstructure may be considered, as necessary to properly distribute loads to the substructure, provided that the superstructure is capable of sustaining such loads. Uplift wind, per AASHTO Article “Overturning Forces,” shall be included in the design where appropriate, for example, on single column piers. Wind loads shall be applied through shear keys or other positive means from the superstructure to the substructure. Wind loads shall be distributed to the piers and abutments in accordance with the laws of statics. Transverse wind can be applied to the piers assuming the superstructure to act as a rigid beam. For large structures, a more appropriate result might be obtained by considering the superstructure to act as a flexible beam on elastic supports. E. Earthquake Loads Earthquake loads on elements of the substructure are describe in the Guide Specifications for Seismic Design of Highway Bridges. The resulting loads shall be taken in any horizontal direction to give maximum design load for the substructure element. Final design acceleration coefficient and site coefficient will be given in the Foundation Report. Earthquake uplift forces shall be designed per Guide Specifications “Hold-Down Devices.” As a minimum, earthquake forces shall be considered to cause a temporary uplift on the substructure equal to 10 percent of the dead load reaction of the superstructure. Where such forces can be developed, the crossbeam, column and footing shall be designed to carry these temporary loads. For concrete superstructures built integrally with the substructure, the substructure elements shall be designed to carry their dead load plus all the elements below them including soil overburden as though they were suspended from the superstructure. (Seal not included). For this condition, the ultimate downward force shall be 1.0 (EQ + Uplift). For structures carried on elastomeric pads or where there is no positive vertical connection, the uplift force from the superstructure shall be neglected. F. Prestressing Effects from Superstructure When cast-in-place, post-tensioned superstructures are constructed monolithic with the piers, the substructure design should take into account frame moments and shears caused by elastic shortening and creep of the superstructure upon application of the axial post-tensioning force at the bridge ends. Frame moments and shears thus obtained should be added algebraically to the values obtained from the primary and secondary Pe moment diagrams applied to the superstructure. If the equivalent uniform vertical load method presented in T. Y. Lin’s text, Reference 6.99-1, is coded into the computer program GTSTRUDL along with axial forces (and moments at bridge ends if they exist), then the output results will represent all of the above mentioned effects. When cast-in-place, post-tensioned superstructures are supported on sliding bearings at some of the piers, the design of those piers should include the longitudinal force from friction on the bearings generated as the superstructure shortens during jacking. When post-tensioning is complete, the full permanent reaction from this effect should be included in the governing AASHTO load combinations for the pier under design.
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BRIDGE DESIGN MANUAL Criteria Substructure Design 9.1.2
General Considerations
Concrete Design for Substructure The class of concrete for substructure units shall normally be as specified below: Seals Footings Pedestals Massive Piers Columns Std. Retaining Walls Wing Walls Crossbeams Retaining Walls Traffic Barriers
Class 4000W Class 4000 Class 4000 Class 4000 Class 4000 Class 3000 Class 4000 Class 4000 Class 4000 Class 4000
Where retaining walls are connected directly to the bridge superstructure and color matching is important, consideration could be given to using Class 4000 in the retaining wall or using pigmented sealer in order that the concrete color will not vary from adjacent portions of the structure.
9.1.3
Application of Loads to Substructure Units A. Live Load For application of live load, see Figure 9.1.1-1. B. Earthquake For earthquake loading, the intermediate pier(s) of each unit of a multispan continuous structure shall be designed to resist the entire longitudinal earthquake force for that unit (unless the end piers are an integral part of the superstructure). The calculated longitudinal movement shall be used to determine the shear force developed by the pads at the abutments. The Modulus of Elasticity of Neoprene at 70˚F (21˚C) shall be used for determine the shear force. However, the force transmitted through a bearing pad shall be limited to that which causes the pad to slip. For single-span structures supported on pads, see Guide Specifications “Design Requirements for Single Span Bridges.”
9-1:V:BDM9
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April 1991
BRIDGE DESIGN MANUAL Criteria Substructure Design 9.2
Piers
9.2.1
Columns
Piers
A. Spacing of Piers and Columns 1.
Pier Spacing Piers normally are spaced to meet the geometric and aesthetic requirements of the site and to give maximum economy for the total structure. Tall piers will generally justify greater spacing (longer spans) than short piers. Difficult and expensive foundation conditions will also justify long spans. Good judgment must be used in determining pier locations on each job.
2.
Multicolumn Spacing Columns shall be spaced to give maximum structural benefit except where aesthetic considerations dictate a modification. The spacing should be selected so that column moments are minimized for dead load. Multiple columns should be considered if earthquake loads control the column design.
3.
Changing Spacing Column and pier spacing is usually set at the preliminary plan stage based on preliminary analysis. The designer may, for structural reasons, after column spacing in a multicolumn pier or change from a single-column pier to a multicolumn pier. Multicolumn piers are generally better suited for handling lateral loads due to wind and/or earthquake. These changes must be reviewed by the supervisor, who will determine if the changes need to be reviewed by the Bridge Planning Engineer or the Bridge Architect. Pier spacing is usually not changed after the preliminary plan stage. However, if substantial structural improvement and/or cost savings can be realized, changes can still be made. The designer should discuss the possibilities of changing the pier spacing or skew with his/her supervisor at the earliest possible time. Changes in pier spacing could affect the Materials Lab’s soils investigation.
B. Section Shape Column section shape shall be selected for strength and aesthetics and shall give proper dimensions for long column action. Columns should be designed so that construction is as simple and repetitious as possible. The diameter of circular columns should be a multiple of one foot. Rectangular sections should have lengths and widths that are multiples of 3 inches. Long rectangular columns are often tapered to reduce the amount of column reinforcement required for strength. Tapers should be kept to one plane for ease of construction. The column shape is determined at the preliminary plan stage. Changes to column size and shape may be made by the designer. Any changes must be reviewed by the supervisor, who will determine if the change needs to be reviewed by the Bridge Planning Engineer or the Bridge Architect. C. Construction Joints Construction joints in columns are normally placed at the top of the footing or pedestal and the bottom of the crossbeam. Optional construction joints with roughened surfaces should be provided at approximately 30-foot vertical spacing.
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Piers
D. Column Reinforcement 1.
Longitudinal Reinforcement The maximum reinforcement ratio (ratio of the steel area to the gross area of the section - As/Ag) shall be 0.06. The minimum reinforcement ratio shall be 0.01. The reinforcement ratio may be reduced to 0.005 provided that all loads can be carried on a reduced section of similar shape such that the selected reinforcement ratio is equal to .01. All dimensions of the section shall be reduced by the same ratio to obtain the reduced section. The properties of the reduced section should not be used to compute K1/r ratios for long columns. Longitudinal reinforcement should extend into the footing and rest on the bottom mat of footing reinforcement with standard 90° hooks. Embedment must be at least 1.25 1dh (1dh is development length of a standard hook). Longitudinal reinforcement should extend into the crossbeam at least 1.25 1d. Hooks should be avoided in the crossbeam. If the crossbeam is not deep enough to develop the bars, 180° hooks generally provide less congestion. A detailed clearance check is essential at the column/crossbeam connection.
2.
Splicing of Longitudinal Reinforcement Column reinforcement shall not be spliced at points of maximum moment, plastic hinge locations, and in columns less than 30 feet long between the top of footing and the bottom of crossbeam. Splices of No. 11 and smaller bars shall be made by lapping the bars. When space is limited, No. 11 and smaller bars can be spliced by welds, an approved mechanical butt splice, or the top bar can be bent inward (deformed by double bending) to lie inside and parallel to the bars below. When the bar size exceeds No. 11, welded splices or an approved mechanical butt splice shall be used. The smaller of the bars being spliced determines the type of splice required. The appropriate weld details shall be shown on the plans and approved mechanical splices are covered in the Standard Specifications. All splices of No. 7 and larger bars shall be staggered. For usual practice in splicing, see Figure 9.2.1-1. Show splice locations on the plans. Where a column is to have an intermediate construction joint, the shortest bar shall project above the joint 60 bar diameters in the case of lap splicing, or 20 bar diameters in the case of welded splices. If the splice is indicated on the plans as “optional,” the method of payment for splice steel shall be defined in the Special Provisions. The Guide Specifications require that splices fall within the middle one-half of the column. For extremely tall columns (where a 60-foot bar length cannot reach the middle half), splices should not be closer than 30 feet from the columns ends.
3.
Ties and Spirals Ties or spirals are required in all columns to resist shear forces and to maintain the column’s structural integrity after catastrophic forces have severely cracked the outer shell. Two section views of transverse reinforcing differentiating the column ends and the typical middle sections should be shown. The column end section will only be used for the confinement zones, where it must both provide confinement and resist shear. Hoops and ties in the confinement zones are normally No. 6 bars. No. 7 bars can be used for hoops and ties, but the concrete cover (1 inch to the tie) must be maintained using the standard radius for a No. 7 bar. Hoops can be made up of several reinforcing elements with 135° hooks extending into the core a minimum of 10 diameters or 6 inches. Ties can have a 180° hook on one end and a 90° hook on the other end. The 180° hook is to be alternated both horizontally and vertically with the 90° hook. The tie is to engage the peripheral
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Piers
hoop and be tied to the longitudinal reinforcement. The designer should check that the 180° hook can fit between adjacent hoops and longitudinal bars. Where confinement is not required, the transverse reinforcing needs to resist the column shear. Crossties outside the confinement zones are usually No. 4 or No. 5 bars. Cross-ties should be spaced so as to leave horizontal openings of 18 inches to 21 inches to allow for placing and consolidating concrete. The area of the transverse reinforcement required to resist the column shear is defined in Article “Column Shear and Transverse Reinforcement” of the Guide Specifications and AASHTO Article “Shear.” The area of transverse reinforcement required for confinement is determined from Guide Specifications Article “Spacing of Transverse Reinforcement for Confinement” for spirals and ties. The area of transverse reinforcing in the confinement zones is the larger of the two requirements. Transverse reinforcement may be provided by spirals, hoops, or cross-ties. See Design Example 9.2B-1 through -5. The general arrangement for column spirals in circular columns is shown in Figures 9.2.1-1 and 2. Note that spirals are to be used for all circular columns including and less than 8 feet diameter. Standard sizes for column spiral use are No. 4 or No. 5 deformed bar, 1/2-inch diameter or 5 /8-inch diameter plain steel bar, or W20 or W31 cold drawn wire. Label these spirals with all three options (for example: No. 4, 1/2-inch diameter or W20 spiral). The pitch shall allow for 1 inch or 11/3 times the maximum coarse aggregate size clearance to allow aggregate to flow through. Anchor spirals at the top and the bottom with a hook that extends into the core a distance of 10 inches past the bend. Twelve feet zero inches is the maximum height normally fabricated. Show full height of the spiral in the bar list; the fabricator will provide required splices. For diameters larger than 8 feet 0 inches, hoops are to be used. Constant dimension rectangular columns shall be detailed as shown in Figure 9.2.1-4 with the use of spirals. The same provisions as a spirally-reinforced circular column apply. The general arrangement for ties in tapered rectangular columns is shown in Figures 9.2.1-5 through 5. The maximum vertical spacing for hoops and ties in the confinement zones and over the length of lap splices is 4 inches for Seismic Performance Categories C and D and 6 inches for Seismic Performance Categories A and B. The vertical opening between layers of confinement reinforcement should be at least 21/2 inches to allow aggregate to flow through. The spacing at lap splices should be shown on the splice detail and tied to the splice location. 4.
Location of Confinement Zones The typical locations of confinement zones for circular columns are shown in Figure 9.2.1-2 and for tapered rectangular columns in Figure 9.2.1-3. The locations of confinement zones are the same for columns of any shape. Column ends that are framed into footings, multicolumn crossbeams, or longitudinal frames must have confinement reinforcing over the maximum of: a.
The lesser of: (1) 1/6 the clear column height, or (2) The maximum column dimension. For wall type piers where plastic hinging occurs only along the weak axis, use the short dimension.
b.
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18 inches.
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Piers
Confinement reinforcing is required to extend into these framed footings, multicolumn crossbeams, etc., the larger of one-half the maximum column dimension and 15 inches, but not more than three-quarters the depth of the crossbeam or footing. Crossbeam and footing steel can be counted as confinement steel as long as it is fully developed at the extended planes of the side of the column. 5.
Column Hinges The area of the hinge bars in square inches is as follows: 1/ (Pu) Pu2 2 + + Vu2 2 4 As =
[
]
0.85 Fy Cos θ
Where: Pu is the factored axial load Vu is the factored shear load Fy is the reinforcing yield strength (60 ksi) θ is the angle of the hinge bar to the vertical The development length required for the hinge bars is 1.25 times that described in AASHTO Article “Development of Flexural Reinforcement.” Figure 9.2.1-6 shows some typical hinge details. Space the ties and spirals to satisfy Article “Spacing of Transverse Reinforcement for Confinement” of the Guide Specifications, AASHTO Article “Shear,” or a maximum of 12 inches (6 inches if longitudinal bars are bundled). Premolded joint filler should be used to assure the required rotational capacity. There should also be a shear key at the hinge bar location. When the hinge reinforcement is bent, additional confinement reinforcing may be necessary to take the horizontal component from the bent hinge bars. The maximum spacing of confinement reinforcing for the hinge is the smaller of that required above and the following: Av Fy Smax =
[
Pu Tan θ V + s 0.85 lh d
]
Where: Av, Vs, and d are as defined in AASHTO Article “Notations” and 1h is the distance from the hinge to where the bend begins. Continue this spacing one-quarter of the column width (in the plane perpendicular to the hinge) past the bend in the hinge bars. E. Column Loads Loads applied to the columns consist of reactions from loads applied to the superstructure and loads applied directly to the columns. The load combinations are described in AASHTO Article “Combination of Loads” and in Chapter 4 of this manual. The Earthquake Load Combination is described in the Guide Specifications, Article “Design Forces for Structural Members and Connections.” For long columns, it may be advantageous to reduce the amount of reinforcement as the applied loads decrease along the column. In these cases, load combinations need to be generated at the locations where the reinforcement is reduced. Computer programs such as YIELD, GROUPLDS, and GPLOAD can be used to combine the loads.
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Piers
9.2 - 5
BRIDGE DESIGN MANUAL Criteria Substructure Design
Piers
Spiral Details for Circular or Rectangular Columns Show splice details on the plans. Figure 9.2.1-2
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Piers
January 1991
9.2 - 7
BRIDGE DESIGN MANUAL Criteria Substructure Design
Piers
Constant Rectangular Column Section Figure 9.2.1-4
9.2 - 8
November 1993
BRIDGE DESIGN MANUAL Criteria Substructure Design
Piers
Tapered Rectangular Column Ties Figure 9.2.1-5
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BRIDGE DESIGN MANUAL Criteria Substructure Design
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Piers
BRIDGE DESIGN MANUAL Criteria Substructure Design 9.2.2
Piers
Column Design A. General Understanding the effects on long columns due to applied loads is fundamental in their design. The following is intended to give further guidance of long column design. 1.
Modes of Failure A column subject to axial load and moment can fail in several modes. A “short” column can fail due to crushing of the concrete or to failure of the tensile reinforcement. A “long” column can fail due to elastic buckling even though, in the initial stages, stresses are well within the normal allowable range. Failure of a long column is normally a combination of stability and strength failure which might occur in the following sequence:
2.
a.
Axial load is applied to the column.
b.
Bending moments are applied to the column, causing movement of the center line with respect to the line of action of the axial loads.
c.
Axial loads act eccentrically to the new column center line producing P-∆ moments which are additive to applied moments.
d.
The P-∆ moments increase the deflection of the column and lead to higher eccentricities and moments.
e.
At some curvature (bending strain), failure of the concrete or reinforcement results in sudden failure of the column.
Peculiarities of Bridge Columns Unlike building columns, bridge columns are required to resist lateral loads through bending and shear. As a result, these columns may be required to resist relatively large applied moments while carrying nominal axial loads. In addition, columns are often shaped to give good appearance. This results in complicating the analysis problem with non-prismatic sections.
B. Slenderness Effects The goal of a slenderness analysis is to estimate the additional bending moments in the columns and the foundations that are developed as a result of axial loads acting upon the deflected structure. The following is intended to supplement and clarify the provisions of the AASHTO Specifications. Valuable information is available in the Commentary on Building Code Requirements for Reinforced Concrete, ACI 318 R-83. Two primary analysis methods exist: Method 1:
The approximate moment magnifier method detailed in AASHTO Article “Approximate Evaluation of Slenderness Effects.”
Method 2:
A second-order structural analysis which accounts directly for the axial forces.
The decision as to which method to use is based upon a consideration of the slenderness ratio (kLu/r) of the column(s). Method 1 is allowable if kLu/r ≤ 100. Method 2 is recommended (by AASHTO) for all situations and is mandatory (Article “Slenderness Effects in Compression Members”) for kLu/r > 100.
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Piers
When compatible assumptions are made, Method 1 is generally more conservative and is easier to apply. For certain structures, however, use of Method 2 can lead to significant economy in the final structure. Determination of (kLu/r) requires an estimate of the value of the effective length factor, k. For unbraced columns, k ≥ 1.2; for braced columns, k ≤ 1.0. 1.
Braced or Unbraced Columns The AASHTO Specifications use the expression “compression members braced against sidesway” in order to establish an effective column length. In a braced member with loads applied at the joints, any tendency toward sidesway is resisted by other members. In building design, bracing is commonly provided by diagonal bracing, shear walls, or similar elements. Bracing for some columns is provided by other columns within a story. Design procedures developed for these situations are not readily adaptable to bridge design since typical bridge columns tend to be dominated by lateral loading while building columns are usually dominated by axial loading. In the transverse direction, sidesway, due to axial loads may be resisted by lateral flexure of the superstructure as a result of the connections at the end piers. The usual practice is to consider the piers as unbraced in the transverse direction. Normal bridge practices is to provide expansion bearings at the end piers. Thus, the columns must resist the longitudinal lateral loading and therefore are considered unbraced. The only time a column can be considered as braced in the longitudinal direction is when it is framed to a bracing member that does not let the column displace more than L/1500, where L is the total column length. In this case, the bracing member must be designed to take all of the horizontal forces.
2.
Effective Length Factor, k The computation of the effective length factor for columns can be readily accomplished by using the charts shown on Design Aid Sheet 9.2-A7. The effective length factor (k) should be computed for both axes of the column. These charts are appropriate only for prismatic members. For nonprismatic columns, k is not used in the column design, a second order analysis is more appropriate. G on these charts is the ratio of the sum of the flexural stiffnesses of the columns to the sum of the flexural stiffnesses of the restraining members. a.
Gtop (1) Transverse Direction When the connection between a single column pier and the superstructure is moment resisting, the torsional rigidity of the superstructure may be accounted for in the computation of the restraining stiffness. In this case, Gtop can be computed as follows:
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Piers Gtop =
4Ec(1.2Ic)/Lc 9.5EsRs/2(1+µs)Ls
where: Ec is the modulus of elasticity of the column Ic is the column moment of inertia computed for the gross section Lc is the column length Es is the modulus of elasticity of the superstructure Ls is the average length of the adjacent connecting spans Rs is the torsional rigidity of the superstructure (the I11 value computed for the computer program SEISAB) µs is Poisson’s ratio for the superstructure (2) Longitudinal Direction When the connection between the pier and the superstructure is moment resisting, Gtop can be computed as follows: Gtop =
4Ec(1.2Ic)/Lc ΣnEs(0.5Is)/Ls
where: Ec, Ic, and Lc are as defined above for the column Es and Ls are for the connecting spans n = 3 for an end span; n = 4 for an intermediate span with fixity at both ends Is can be taken as the I33 value computed for the computer program SEISAB AASHTO Article “Approximate Evaluation of Slenderness Effects” requires that the effect of cracking and reinforcement on the relative stiffnesses must be considered when determining k. The use of 1.2Ic for the column stiffness approximates the effect of the column reinforcement. The use of 0.5Is and 0.5Rs for the superstructure accounts for the effects of cracking. More rational approaches may be considered in some cases. b.
Gbot By definition, Gbot = Kcol/KR, where: Kcol = flexural stiffness of the column Kcol = 4Ec(1.2Ig)Lu for a prismatic column KR = rotational stiffness constant describing the restraint of the foundation The rotational stiffness constant, KR, is related to the base fixity, γ, as follows: Given KR, γ =
KR KR + Kcol
or given γ, KR , = [γ /(1- γ)]*Kcol Therefore, Gbot = (1- γ)/γ Note that
January 1991
0 ≤ γ (free)
≤
1.0 (fixed)
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Procedures for establishing KR and/or γ will be discussed in Chapter 4, “Foundation Modeling.” In most cases, there is a substantial amount of uncertainty involved in the computation of KR or γ. Therefore, care must be taken to use conservative values in the slenderness analysis. For preliminary design or when detailed foundation information is not available, an approximate, conservative value for base fixity, γ, should be used. In this case, Gbot should not be taken ≤ 1.0. (1) Piers on multiple rows of piles are 100 percent fixed at the connections to the piles. (2) Piers on a single row of piles are pinned at the connection to the piles. (3) Piers on spread footings: (a) allowable* soil pressure of 3-6 TSF; γ = 0.3, (b) allowable* soil pressure of 6-9 TSF; γ = 0.4, (c) allowable* soil pressure 9 TSF (competent rock); γ = 1.0. *at service load level If additional information becomes available, the effective length of the column(s) should be recalculated. When the new effective length is significantly different, the design should be checked using the new values. Lower limits on k values: k ≥ 1.2 for unbraced columns with rotational restraint at both ends, k ≥ 2.1 for unbraced columns with no rotational restraint at one end (i.e., cantilever column). For braced columns, a value of k = 1.0 will normally be used. c.
Alternate Procedure for Determining Base Fixity, γ The moment induced in columns is dependent on the rotational restraint at the top and the degree of fixity at the base. In turn, the base fixity is dependent on the connection between the column and the footing, and the resistance of the soil to footing rotation. For most cases, it is adequate to assume a base fixity between 0.5 and 1.0, but in some cases a more detailed analysis is warranted. The degree of fixity between a column and a footing is a function of several factors including the size and spacing of anchor bolts, thickness of base plate, grout strength, etc. The degree of fixity or restraint, γ, between the footing and soil, assuming a fixity of 1.0 in the column-footing connection, can be calculated from: γ=
kIf
kIf + 4EccIc/h where: k = Soil modulus, similar to “Modulus of Subgrade Reaction,” used in paving design. Where this value is not available, it can be estimated from Figure 9.2.2-2. Because the equation is not sensitive to values of k, these values will usually be adequate, psi/in. If = Moment of inertia of the plan of the footing in the direction of bending, in.4. Ic = Moment of inertia of the column, in.4. h = Height of column, in. Ecc = Modulus of elasticity of concrete in column, psi. 9.2 - 14
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Figure 9.2.2-2 modulus, k.
Approximate relationship between allowable soil bearing value and subgrade
C. The Moment Magnification Method This method can lead to rapid column design. The procedure for its use is well defined in the AASHTO Specifications. Design Aid Sheets 9.2-A1 through 9.2-A6 can be helpful for design by this method. 1.
General Procedure The following information is required: • Column geometry and properties: E, I, Lu, and k. • All ultimate group loads and column understrength factors, φ (see Figure 9.2.2-1), obtained from conventional elastic analyses using appropriate stiffness and fixity assumptions. The basic procedure is as follows: a.
Compute Pc for all columns per AASHTO Article “Approximate Evaluation of Slenderness Effects.”
b.
Check Pu* ≤ .7Pc. Pu* is the load at the top of the column plus a portion of the column weight: Pu* = Putop + 1/3 * factored column weight. This ensures that Euler buckling is not approached.
c.
Compute the moment magnification factors as specified in AASHTO using Pu*. Since φ may vary for different columns for the same load group, Equation 8-41a is modified as follows: δs =
d.
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1 ≥ 1.0 1-(ΣPu*/ΣφPc)
Compute the magnified factored moments, Mc, as specified in AASHTO Equation 8-40. M2b is defined by the specifications as the bending moment due to gravity loads which result in no appreciable sidesway (∆ < Lu/1500). Since creep, shrinkage, post-tensioning effects, and thermal deformations do not result in sidesway of the entire frame, it is considered appropriate to include those moments in the definition of M2b. This provision applies only to those columns framed together by the superstructure and/or a crossbeam. Note that the use of Equation 8-40 will generally require that Pc be computed for both the unbraced and the braced conditions.
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PHI Factor Figure 9.2.2-1
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Critical Load, Pc The critical load, Pc, can be readily computed for a prismatic column. For a nonprismatic column, however, the computation becomes more difficult. Numerical methods are available for solving this problem accurately; the computer program COLUMN can be used if an estimate of the effective length factor (k) is made. Other numerical methods require that the rotational restraint at the column ends be input directly (the effective length is not required).
3.
Biaxial Bending When using the AASHTO specifications regarding bending about both principal axes, the appropriate values of Pc and moment magnifiers must be computed for each axis separately.
4.
Yield Program Economy in design time can be achieved by using the program YIELD. The program groups the AASHTO loads, magnifies the moments, and checks or designs the column steel. Under the check mode, it will determine the Plastic Hinging Moment Envelope to determine foundation loads. The moments are all assumed to be acting on an unbraced column; therefore, the results will be conservative. If magnification factors controlling the column design exceed 1.4, the designer should use either the more correct method described above or a second-order analysis described in the following section.
D. Second-Order Analysis 1.
General A second-order analysis which includes the influence of axial loads on the deflected structure is required under certain circumstances and may be advisable in others. It can lead to substantial economy in the final design of many structures. Performing a second-order analysis can be difficult and time consuming. The designer should consider all of the options carefully and should discuss the situation with the supervisor before proceeding with the analysis. The ACI Building Code Commentary (ACI 318 R-83) discusses some general aspects of carrying out a second-order analysis. Some additional aspects which should be considered are given here. Previous practice has been to analyze columns separately. This is appropriate only for those columns that are isolated structurally from the frame as a whole (with sliding bearings in the direction of interest). For columns framed together, the entire frame should be analyzed as a unit. Analyzing individual columns results in overly conservative results for some columns and nonconservative results for others. This is a result of redistribution of the lateral loads in response to the reduced stiffnesses of the compression members. For example, in a bridge with long, flexible columns and with short, stiff columns both integrally connected to a continuous superstructure, the stiff columns will tend to take a larger proportion of the lateral loading as additional sidesway under axial loads occurs. For a second-order analysis, loads are applied to the structure and the analysis results in member forces and deflections. It must be recognized that a second-order analysis is non-linear; thus, the commonly used principle of superposition may not be applicable. The loads applied to the structure should be the entire set of factored loads for the load group under consideration. The analysis must be repeated for each group load of interest. The problem is complicated by the fact that it is often difficult to predict in advance which load groups will govern.
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As with a conventional linear elastic frame analysis, various assumptions and simplifications must be made in regard to member stiffness, connectivity, and foundation restraint. Care must be taken to use conservative values for the slenderness analysis. For compression members, use of the equations for EI stated in AASHTO Article “Approximate Evaluation of Slenderness Effects” will give an adequately conservative value. For concrete beams, use EI = 0.5EcIg. This is inexact in that reinforcement, cracking, load duration, and their variation along the members are not explicitly taken into account. More precise methods may be used. Foundation restraint will often be modeled as rotational springs (lateral and vertical springs may also be incorporated). A stiffness matrix may be computed to represent the soil-foundation interaction. Procedures to compute these values will be discussed in Chapter 4, “Modeling Foundations.” For certain loadings, column moments are sensitive to the stiffness assumptions used in the analysis. For example, loads developed as a result of thermal deformations within a structure may change significantly with changes in column, beam, and foundation stiffnesses. Accordingly, upper and lower bounds on these stiffnesses should be determined and the analysis repeated using both sets to verify that the governing load has been found. The specifications include the strength reduction factor, φ, in the computation of the moment magnifiers. No guidance is given with respect to the use of φ in a second-order analysis scheme. The following procedure is adopted: • For the lower-bound analysis, use the reduced member stiffnesses discussed earlier and the lower-bound foundation restraint stiffness values. Multiply the member stiffnesses by the appropriate reduction factor: φ = 0.9 for beams, and φ varies for columns. • For the upper-bound analysis, use stiffness assumptions normally employed for elastic analysis; IB = Ig, IC = 1.2Ig, and the upper-bound foundation restraint stiffnesses. The stiffnesses for the upper-bound analysis should not be reduced (φ = 1.0). E for concrete varies with loading type; thus, some superposition of results may be required in spite of the non-linearity of the analysis. In most cases, the non-linear effects will be small for the relatively stiff upper-bound analysis. Judgment is required. Note: Computations of effective length factors, k, and buckling loads, Pc, are not required for a second-order analysis, though they may be helpful in establishing the need for such an analysis. In general, if magnification factors computed using the AASHTO Specifications are found to exceed about 1.4, then a second-order analysis may yield substantial benefits. Methods for satisfying the requirements of a second-order analysis are given as follows:
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a.
The preferred method for performing a second-order analysis of an entire frame or on isolated single columns is to use the program GTSTRUDL with appropriate stiffness and restraint assumptions. The columns are divided into a number of individual segments (10 gave good results in tests). The factored group loads (including the self-weight of the columns) are applied to the frame. The model is then analyzed using the nonlinear option available in GTSTRUDL. The final design moments are obtained directly from the analysis. Care must be taken in modeling complex structures as the cost of a nonlinear analysis can be high.
b.
For isolated single columns, the program COLUMN gives the magnified moments directly (P-∆ moments are added to the applied moments using an iterative process until stability is reached).
BRIDGE DESIGN MANUAL Criteria Substructure Design c.
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For isolated single columns, the program LPILE1 can be manipulated to also give the magnified moments directly. Note: Neither of these programs, COLUMN nor LPILE1, includes the effect of the column weight; therefore, the axial load must be adjusted as follows: Pu* = Pu + 1/3 * factored column weight. Care and judgment must be used as they have limitations on the boundary conditions and configurations that may be analyzed.
d.
For isolated single columns, the iterative hand method is sometimes economical. Loads affected by column stiffness (temperature, shrinkage, and post tensioning) cannot be analyzed this way. The factored load is applied to the column and the deflections are computed along the length of the member taking into account restraints top and bottom and the effect of variations in moment and I along the length of the column. The load is adjusted for the P-∆ moment. The adjusted loads are applied to the column and the deflections are computed again. The deflections usually converge in about five iterations (deflections from last cycle are within 5 percent of the total deflections). If not, the column is too flexible and is unstable for that load. The program LOTUS can be used to do the repetitious hand calculations. Column EI must be adjusted according to AASHTO Article “Approximate Evaluation of Slenderness Effects.” Pu* including one-third the factored column weight must not exceed .7Pc. *At service load level.
2.
Special Provisions for Seismic Loading The following applies to those structures designed according to the AASHTO Guide Specifications for Seismic Design. The seismic analysis program SEISAB does not include the secondary effects of the axial loads. Therefore, a modified approach is necessary to perform a second-order analysis for this loading. The moment magnifier method magnifies the Group VII loads as follows: Mu = δbMDL + δs(MEQ/R) where MEQ is the elastic seismic moment obtained from SEISAB and R is the response modification factor defined in the Guide Specifications. The design philosophy of the Guide Specifications may be summarized as follows: The columns are designed to hinge (fail in flexure) at a specified percentage of the computed fully elastic seismic moment. This will occur at a deflection and shear force corresponding to δsMEQ/R. At this point, inelastic deflection will continue to some unknown maximum, but bending moments and shear forces in the columns will theoretically not increase. Therefore, the problem is to come up with an approach to compute the additional design moment due to slenderness effects, M, such that: MEQ/R + M = δsMEQ/R. A suggested second-order analysis is given as follows: Estimate the maximum primary elastic deflection of the frame: ∆PR = ∆EQ/R where ∆EQ is the CQC elastic deflection computed from SEISAB.
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Apply ∆PR to a GTSTRUDL model of the frame. This will yield a set of primary deflections and forces, MPR and VPR, corresponding to ∆PR. (Note that for some structures, these forces may not agree exactly with the SEISAB results.) Apply the external gravity loadings and the primary lateral force determined above to the original model. Use the nonlinear option of GTSTRUDL to analyze the structure. The final moments (MF) obtained are then equal to the sum of the primary moments (MPR) and the additional moments due to slenderness effects (M). Thus, the design moments for the columns are given by: Mu = MDL + MEQ/R + M where: M = MF - MPR obtained from the GTSTRUDL analysis. Note: The response modification factor, R, used for footing or pile design is generally less than the value used for the columns. Thus, a separate analysis may be required to obtain the footing design moments. E. Resisting Capacities Once magnified moments have been established, the resisting capacity of the column section must be made adequate to carry this magnified moment. The appropriate capacity reduction factor (φ) must be used in the computation of this resisting capacity. In addition, the superstructure and the foundation must also be designed to resist this magnified moment. 1.
Reduction Factor (φ) According to AASHTO Article “Design Strength,” the reduction factor (φ) may be increased linearly from the value for compression members to the value for flexure as the design axial load strength, φPn, decreases from .10fc′Ag or the balanced load strength φPb, whichever is smaller, to zero. Since moment capacities are based on the factored axial load, Pu, this axial load is equal to the design axial load strength, or Pu = φPn. The balanced load strength can be less than .10fc′Ag when the area of reinforcement in tension of the column exceeds .02Ag. This is rarely the case in column design but can be the case in pile design. According to the Guide Specifications Article “Flexural Strength,” for Seismic Performance Categories C and D, the value of φ for Group VII Loading may be increased linearly from .50 to the value for flexure when the stress due to the maximum axial load decreases from .20fc′Ag to zero. Figure 9.2.2-1 shows a graph of φPn versus φ. This graph is appropriate unless φPb is less than .10fc′Ag. Computer program YIELD computes φ according to this graph.
2.
Moment Capacity Computer programs such as YIELD and ULT2AX can be used to compute the moment strength, φMn. The program YIELD computes the moment strength in the direction of the resultant Mx and My. The program ULT2AX computes the moment strength in the direction given in the input; therefore, the φMn curve must be plotted for the axial load strength, Pn. The resultant of Mux and Muy must fall within the curve.
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F. Service Load Requirements When widening bridges originally designed by the allowable stress method, the analysis procedure for the Moment Magnification Method is as follows. Compute the capacity of the column by load factor design procedures. The allowable service load capacity of the column shall be taken as: Mallow =
0.35 φ Mn δ
where: δ=
Cm 1 - 2.5P/Pc
and P is the service axial load G. Seismic Design of Multicolumn Bents The Guide Specifications require that connections to the superstructure be designed for either the elastic demand moment (Seisab Load Case 2) at the top of the column using an “R” of “1,” or the plastic moment capacity of the top of the column, whichever is less. These column moments are to be carried into the crossbeam and accounted for in the design. (For a center column of a three-column bent, the moment is distributed to the crossbeam on either side of the column.) The seismic design moment for the crossbeam would then be the moment at the face of the column or the equivalent square column.
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9.3.1
Size and Construction Details
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A. Representative Types Several representative types of abutments that have been used by the Bridge and Structures Division are shown in Figure 9.3.1-1. The types shown are intended for guidance only and may be varied to suit the type of bridge being designed. B. Bearing Seats The bearing seats shall be wide enough to accommodate the size of the bearings used with a minimum edge dimension of 3 in. and satisfy the requirements of the Guide Specification for Seismic Design of Highway Bridges, Article “Design Displacements.” On L-abutments, the bearing seat should be sloped away from the bearings to prevent a build up or pocket of water at the bearings. The superelevation and profile grade of the structure should be considered for drainage protection. Normally, a 1/4 in. drop across the width of the bearing seat is sufficient. C. Bearing Restraints and Girder Stops All structures shall be provided with some means of restraint against lateral displacement at the abutments due to earthquake, temperature and shrinkage, wind, earth pressure, etc. Such restraints may be in the form of concrete hinges, concrete girder stops with or without vertical elastomeric pads, or pintles in metal bearings. Other solutions are possible. Article “Connection Design Forces” of the Guide Specifications for Seismic Design of Highway Bridges describe longitudinal linkage force and hold-down devices required. To eliminate alignment conflicts between prestressed girders and girder stops, prestressed girders should be placed in final position before girder stops are cast. Allow 1/8 in. clearance between the prestressed girder flange and the girder stop to prevent binding. Incorporate details of Figure 9.3.1-2 in bridge plans. D. Face Slope A vertical abutment wall or a 1:4 slope is used on the front face of the abutment as shown on Design Aid Sheets 9.3-A2 through 9.3-A6. On very high abutments, where a 1:4 slope would create an excessively wide bearing seat, the slope should be adjusted or using the slope only at the exposed leading edge of the abutment and wing wall while leaving the remaining abutment wall surface vertical. On abutments with fractured fin surface, the front face should be vertical to match the fractured fins. E. Sizing Abutments Other portions of the abutment shall be sized for stress. As indicated in Figure 9.3.1-1, additional stem width, where required, may be obtained by sloping the back face of the wall. On extremely high walls (30 feet and above) subjected to large earth pressures, consideration should be given to using counterfort construction. See Section 9.4.2 B of this manual, Counterfort Retaining Walls. F. Class of Concrete The class of concrete used in abutments and standard wingwalls shall be Class 4000.
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G. Abutment and Retaining Wall Junctions Vertical expansion joints extending from the top of footings to the top of the abutment are usually required between abutments and adjacent retaining walls to handle anticipated movements. The expansion joint is normally filled with premolded joint filler which is not water tight. There may be circumstances when this joint must be water tight; 1/8 butyl rubber may be used to cover the joint. The open joint in the barrier should contain a compression seal to create a water tight joint. Figure 9.3.1-3 shows typical details that may be used. Aesthetic considerations may require that vertical expansion joints between abutments and retaining walls be omitted. This is generally possible if the retaining wall is less than 60 feet long. The footing beneath the joint may be monolithic or cast with a construction joint. In addition, dowel bars may be located across the footing joint parallel to the wall elements to guard against differential settlement or deflection. For further discussion, see Section 9.4, Retaining Walls. Particular attention should be given to the horizontal reinforcing steel required at the junction between abutment and retaining wall. To account for the resistance to rotation found in retaining walls and cantilever abutment walls rigidly connected to one another in a U-shape (as seen in Plan View), an equivalent fluid pressure of 45 pcf shall be assumed for design. This increased loading can normally be reduced to 30 pcf at a distance, from the junction between the abutment and retaining wall, equal to the average height of the wall under design. At this location, active state soil pressure is assumed to be developed. H. Construction Joints To simplify construction, vertical construction joints are often necessary, particularly between the abutment and adjacent wing walls. Construction joints should also be provided between the footing and the stem of the wall. Shear keys shall be provided at construction joints between the footing and the stem, at vertical construction joints or at any construction joint that requires shear transfer. The Standard Specifications cover the size and placement of shear keys. The location of such joints shall be detailed on the plans. Construction joints with roughened surface can be used at locations (except where needed for shear transfer) to simplify construction. These should be shown on the plans and labeled “Construction Joint With Roughened Surface.” When construction joints are located in the middle of the abutment wall, a pour strip should be used for a clean joint between pours. Details of the pour strip should be shown in the plans. See Section 5 of this manual and Design Aid Sheets 9.3-A1 through A6 for further guidance on construction joints. I.
Drainage and Backfilling Three-inch (3 in.) weep holes shall be provided in all bridge abutment walls. These shall be located 6 inches above the final ground line at about 12 feet on centers. In cases where the vertical distance between the top of the footing and the bearing seat is greater than 10 feet, additional weep holes shall be provided 6 inches above the top of the footing. No weep holes are necessary in cantilever wing walls where a wall footing is not used. The details for gravel backfill for walls, underdrain pipe and backfill for drains shall be indicated on the plans. The gravel backfill for walls shall be provided behind all bridge abutments. The underdrain pipe and gravel backfill for drains shall be provided behind all bridge abutments except abutments on fills with a stem wall height of 5 feet or less. When retaining walls with footings are attached to the abutment, a blockout may be required for the underdrain pipe outfall. Cooperation between Bridge and the district as to the drainage requirements is needed to guarantee proper blockout locations.
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Underdrain pipe and gravel backfill for drains are not necessary behind cantilever wing walls. Threefoot (3 ft.) thickness of gravel backfill for walls behind the cantilever wing walls shall be shown in the plans. The backfill for walls, underdrain pipe and gravel backfill for drains are not included in bridge quantities, the size of the underdrain pipe should not be shown on the plans. Figure 9.3.1-4 illustrates backfill details. J.
Embankment at Bridge Ends The minimum clearances for the embankment at the front face of abutments shall be as indicated on Standard Plan Sheet H-9. At the ends of the abutment, the fill may be contained with wing walls or in the case of concrete structures, placed against the exterior girders. On stub abutments with the end diaphragm cast on the superstructure, the open expansion joint must be protected from the fill. Normally, 1/8 in. butyl rubber is used to seal the opening. Figure 9.3.1-5 and Figure 9.3.1-6 show typical details using butyl rubber. The bearings must also be protected from the fill. Figure 9.3.1-7 and Figure 9.3.1-8 show typical details to protect the bearings. There are many other different ways to protect the open expansion joints and bearings than shown in Figures 9.3.1-5 through 8. The method used should be well detailed in the plans. The Special Provision and Estimates unit can advise as to what types of materials would or would not require special provisions.
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Open Joint Details — End Diaphragm on Girder Figure 9.3.1-7
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Abutment Loads A. Applicable Loads In general, bridge abutments will be subjected to the following loads: Dead load reaction of superstructure. Dead load reaction of approach slab, where applicable, taken as 2 kips per foot of wall applied at the pavement seat. Live load surcharge on earth pressure shall not be included with this load. Weight of the abutment itself. Weight of wing walls where applicable. Weight of backfill and toe fill usually taken as 125 pcf. Frame shortening of post-tensioned superstructure where applicable. Buoyancy where applicable. Live load reaction from superstructure without impact. Live load reaction from approach slab, where applicable, taken as 4 kips per foot of wall for HS-20 loading, 3 kips per foot for H-20 and HS-15 loading and 2 kips per foot for H-15 loading applied at the pavement seat. Live load surcharge on earth pressure shall not be included with this load. Earth pressure is normally taken at 30 pcf equivalent fluid pressure for group loads I through VI. For group load VII, an equivalent fluid pressure with a rectangular distribution and a magnitude of 1/2 γ H(KAE-KA) is added to the earth pressure. Where γ is the unit weight of the backfill (normally taken as 125 pcf), H is the height of the wall, KA is the Coulomb active pressure coefficient, and KAE is the Mononobe-Okabe active pressure coefficient for earthquake as described in the Guide Specifications for Seismic Design of Highway Bridges. Live load surcharge on earth pressure where applicable, normally taken as a 2-foot surcharge, causes a vertical and horizontal reaction. Dead load reaction of approach slab and live load reaction from approach slab shall not be included with this load. Earthquake transmitted through bearings, girder stops, or a rigidly attached superstructure. Seismic inertia force of the substructure, taken as the horizontal acceleration coefficient (1/2 acceleration coefficient) times the weight of the abutment (including footing and soil weight). This force acts horizontally in the same direction as the earth pressure, at the mass centroid of the abutment. This is described in the Guide Specifications for Seismic Design of Highway Bridges. Seismic inertia force is only applied for stability and sliding analysis, it is not to be applied to determine the reinforcement required in the abutment. Longitudinal live load from superstructure. Temperature and shrinkage. Centrifugal force. Wind load from superstructure. Figure 9.3.2-1 shows the typical loads applied to an L-abutment and Figure 9.3.2-2 shows the typical loads applied to a cantilever abutment. Figure 9.3.2-3 shows longitudinal and transverse forces from the superstructure with a skew.
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B. Usual Governing Load Combinations The AASHTO Specifications for load combinations supplemented by Bridge Division Criteria shown in Chapter 4 of this manual apply in the design of abutments. Normally for the design of abutments, only Group I (Service Load) and Group IV and VII (Load Factor) need to be checked. For abutment footing design loadings, see Section 9.5. The designer should consider other groups if it appears they might be critical. For the typical abutment with wing walls, check the outer 10-foot portion of the abutment with wing wall and approach slab. Beyond the 10-foot section, check the abutment without applying the wingwall and approach slab (using the live load surcharge on earth pressure). In Group I and IV, apply live load surcharge with and without the live load reaction from the superstructure. Both the vertical and horizontal component of live load surcharge on earth pressure should have the appropriate live load factor applied to it. C. Special Handling of Lateral Forces The longitudinal forces from the superstructure is normally transferred to the abutments through the bearings. The calculated longitudinal movement shall be used to determine the shear force developed by the bearing pads at the abutments. The Modulus of Elasticity of Neoprene at 70°F (21°C) shall be used for determining the shear force. However, the force transmitted through a bearing pad shall be limited to that which causes the bearing pad to slip. Normally, the maximum load transferred through a teflon sliding bearing is 6 percent and through an elastomeric bearing pad is 20 percent of the dead load reaction of the superstructure. For Group VII (Seismic), assume no load transfer through the bearings because end diaphragm is in contact with abutment wall. The bearing force shall not be added to seismic earth pressure forces. The transverse forces from the superstructure is transferred to the abutment through the girder stops or the bearings. 1.
Special Abutment Loads a.
Cantilever abutment with end diaphragm cast on superstructure: For structures without expansion joints, the earth pressure against the end diaphragm is transmitted through the superstructure.
b.
Cantilever L-abutment: The compressibility of the expansion joint shall be considered in the design of the abutment for earthquake, temperature, and shrinkage when these forces increase the design load.
The following cases will illustrate the handling of typical longitudinal forces: 2.
Case A — Force in Direction of Span The intermediate pier(s) of a multi-span continuous structure shall be designed to resist the entire longitudinal force of the superstructure (unless the end piers are an integral part of the superstructure). The calculated movement at the abutments determined from analysis of the superstructure shall be used to determine the shear force developed by the bearing pads. The limiting bearing pad force shall be as indicated above. For the earth pressure force, use the βE factor (see Section 4.2), associated with earth pressure tending to decrease stability (cause overturning), except for group load VII, bE shall be taken as 1.0.
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Case B — Force in Direction of Backfill The force in the bearing pad caused by longitudinal superstructure movements shall be calculated in a manner similar to Case A. The βE factor for this case shall be the one associated with earth pressure tending to increase stability (resist overturning), except for group load VII, βE shall be taken as 1.0.
4.
Case C — Temporary Construction Condition (longitudinal forces in either direction) a.
Superstructure Built Before Backfill at Abutment In some cases the superstructure of a bridge may be built and falsework underneath released before backfill is placed at the end abutments. At this stage the structure may be subjected to earthquake, wind or other horizontal forces. The factor (see Section 4.2) associated with these forces shall be taken as 1.1 owing to the temporary nature of the condition, except for group load VII where the factor shall be taken as 1.0 The force in the bearing pad shall be calculated as in Case A. In some instances, this loading condition may govern the design and might be severe enough to require very large footings or excessive amounts of reinforcing steel when compared with loading combinations that include earth pressure and overburden. Rather than trying to design for severe loading conditions, the designer should consider recommending to the district that backfill be placed before construction of the superstructure. If agreed to, note this in the sequence of construction on the plans.
b.
Superstructure Built after Backfill at Abutment If the superstructure is to be built after the backfill is placed at the abutments, the resulting temporary loading on the abutments will cause them to act like retaining walls. Such walls require additional tensile reinforcement in the top of the footing heel. The bottom of the footing will normally require tensile reinforcement extending from the heel to the toe once the superstructure is completed.
c.
Sequence of Falsework Removal Another temporary construction condition to be considered is the sequence of falsework removal. For example, it is usually advantageous in sizing the footing to release the falsework from under the wing walls after some portion of the superstructure load is applied to the abutment. This item, when applicable, can be covered by a note in the sequence of construction on the plans.
5.
Special Considerations When the force transmitted through the bearing pads is very large, the designer should consider increasing the bearing pad thickness, using TFE sliding bearings and/or utilizing the flexibility of the abutment as a means of reducing the horizontal design force. When the flexibility of the abutment is considered, it is intended that a simple approximation of the abutment deformation be made.
January 1991
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BRIDGE DESIGN MANUAL Criteria Substructure Design
9.3 - 18
Abutments
BRIDGE DESIGN MANUAL Criteria Substructure Design
Abutments
D. Load on Girder Stop Bearings For skewed structures with earth pressure against the end diaphragm (see Figure 9.3.2-4), the need for girder stop bearings shall be investigated. When required, these bearings are placed vertically against the girder stop to transfer the skew component of the earth pressure to the abutment without restricting the movement of the superstructure in the direction parallel to centerline. The design procedure for elastomeric girder stop bearing pads for Series 8, 10, and 14 Prestress Girders is shown in Chapter 8, Appendix A of this manual. In some cases bearing assemblies containing sliding surfaces may be necessary to accommodate large superstructure movements. Girder stops are often required to transfer earthquake load from the superstructure to the abutment. In these cases, all components of the girder stop, including the bearing assembly, shall be designed for the earthquake loading in addition to the earth pressure described above. E. Loads on Girder Stops The loads mentioned in Section 9.3.2 D above apply to girder stops and superstructure restraints. Girder stops are designed using shear friction theory. The possibility of torsion combined with horizontal shear when the load does not pass through the centroid of the girder stop shall also be investigated. Some type of transverse girder stop is required for all abutments.
9.3.3
General Design Procedures A. Design for Stability The factors of safety against overturning and sliding shall be as specified in Section 9.3.2 A(d) of this manual. Special requirements for individual abutments types are covered in Section 9.3.4 A through E. Also see Section 9.5, Footings. B. Earth Pressure at Front Face In the usual case, the earth pressure exerted by the fill in front of the abutment is neglected in the design. The weight of the fill in front of the abutment should be included in the analysis for overturning if it adds to overturning. C. Design for Strength When the primary structural action is parallel to the superstructure or normal to the abutment face, the wall shall be treated as a column subjected to combined axial load and bending moment. Compressive reinforcement need not be included in the design of cantilever walls, but the possibility of bending moment in the direction of the span as well as towards the backfill shall be considered. A portion of the vertical bars may be cut off where they are no longer needed for stress. For footing design see Section 9.5, Footings. In addition, see the special requirements for individual abutment types under Section 9.3.4 A through E. D. Minimum Reinforcement 1.
Minimum Wall Steel The minimum area and maximum spacing of stressed wall reinforcement stipulated in AASHTO Specifications shall be furnished.
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BRIDGE DESIGN MANUAL Criteria Substructure Design 2.
Abutments
Minimum Temperature and Shrinkage Steel in Wall The AASHTO Specifications, Article “Shrinkage and Temperature Reinforcement,” requires a minimum temperature and shrinkage steel of 0.125 sq. in. per foot of wall. This is not sufficient to limit shrinkage cracks in thick walls. A more appropriate minimum temperature and shrinkage steel is taken from the ACI-83, minimum area of reinforcing steel per foot of the wall, in both directions on each face of the wall, shall be 0.011 times the thickness of the wall (in inches), spaced at 12 inches. On abutments that are longer than 60 feet, consideration should be given to have vertical construction joints to minimize shrinkage cracks.
3.
Minimum Cross Ties in Wall Ties, no. 4 bars with 180 degree hooks, spaced at approximately 2 feet center to center vertically and at approximately 4 feet center to center horizontally shall be furnished throughout the abutment stem in all but stub abutments, see Figure 9.3.3-1.
9.3.4
Load and Reinforcement Requirements A. Requirements for Pile Cap Abutments Earth pressures on some pile caps are either negligible or very small (when the lateral force on each pile is less than 6 kips), and vertical dead load and live load are the major effects. The design of this type of abutment is like that of a crossbeam, and transverse bending as well as shear shall be investigated for the spans between the piles. For the analysis of the pile cap, the wheel loads should be placed for the maximum moment on the pile cap. For the analysis of the piles, the wheel loads should be placed unsymmetrically to obtain the largest pile reaction. For narrow bridges (one-lane ramps and two-lane bridges without skew) the transverse live load moment on the abutment shall be taken about the center of gravity of the pile group assuming the abutment to be a rigid beam. The maximum pile reaction from transverse effect will then be P/N + Mt/S, where P is the total vertical load, N is the total number of piles, Mt is the transverse moment about the centerline of abutment and S is the transverse pile modulus. This analysis is only valid if the lateral forces from earth pressure, etc. are less than 6 kips per pile and all the piles have no batter. For wide bridges (2 lanes with skew and wider) the abutment may be assumed to act as a flexible beam on knife-edge supports. The maximum pile live load reaction from transverse loading can be obtained by assuming the abutment acts as a simple beam between piles and each wheel load (in the design lane or approach lane) is proportionally distributed to the adjacent piles (see Figure 9.3.4-1). Transverse moments and shears may be found assuming the spans between piles as semi-simply supported: i.e. maximum positive or negative moment = 0.80 times the simple beam moment. Maximum shear = simple beam shear. This analysis is valid for piles with a stiffness much less than the pile cap. For pile caps with lateral loads greater than 6 kips, with battered piles, or for piles with a stiffness about the same magnitude as the pile cap, such as shafts, the analysis for the pile cap should be as a crossbeam, see Section 9.2.1, and the analysis for the piles should include the lateral capacity of the pile, see Section 9.6. B. Requirements for Stub Abutments For stub abutment (girder seat to top of footing less than approximately 4 feet), the footing and wall can be considered as a continuous inverted T-beam. The analysis of this type abutment shall include investigation into both bending and shear stresses parallel to centerline of bearing. If the superstructure is relatively deep, earth pressure combined with longitudinal forces from the superstructure may become significant (see Section 9.3.4 C).
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BRIDGE DESIGN MANUAL Criteria Substructure Design
January 1991
Abutments
9.3 - 21
BRIDGE DESIGN MANUAL Criteria Substructure Design
Abutments
Pile Cap Abutment Figure 9.3.4-1
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Abutments
C. Requirements for Cantilever Abutments If the height of the wall from the bearing seat down to the bottom of the footing exceeds the clear distance between the girder bearings, the assumed 45° lines of influence from the girder reactions will overlap, and the dead load and live load from the superstructure can be assumed equally distributed over the abutment width. The design may then be carried out on a per foot basis as described earlier under Section 9.3.3 A through C. The primary structural action takes place normal to the abutment, and the bending moment effect parallel to the abutment may be neglected in most cases. The wall is assumed to be a cantilever member fixed at the top of the footing and subjected to axial, shear, and bending loads. D. Requirements for Spill-Through Abutments The analysis of this type of abutment is similar to that of an intermediate pier. The crossbeam shall be investigated for vertical loading as well as earth pressure and longitudinal effects transmitted from the superstructure. Columns shall be investigated for vertical loads combined with horizontal forces acting transversely and longitudinally. For earth pressure acting on rectangular columns, assume an effective column width equal to 1.5 times the actual column width. Short, stiff columns may require a hinge at the top or bottom to relieve excessive longitudinal moments. E. Requirements for Rigid Frame Abutments Abutments which make up parts of rigid frame bridges shall be designed in accordance with service load criteria. Whenever a preliminary analysis establishes that the effects of vertical loads are far greater than the effects of horizontal earth pressure loads (generally the case with low abutments and long horizontal spans), load factor criteria may be used. Earth pressure loading shall be a maximum of 60 pcf equivalent fluid pressure and a minimum of 30 pcf equivalent fluid pressure to be applied in any combination except as noted below. The 60 pcf value is to be used for normal rigid frames where there is a high degree of restraint to the soil mass. Lower figures may be used if lower degree of restraints exist. The 30 pcf value is equivalent to a normal cantilever retaining wall. Earth pressure loading of up to 15 pcf may be used to reduce moments in the superstructure provided that such pressure can be developed. This reduction may also be used for earthquake acting on rigid frame structures. Earthquake forces from the soil mass need not be applied as loads. The abutment design should include the live load impact factor from the superstructure. However, impact shall not be included in the footing design. The rigid frame itself should be considered restrained against sidesway for live load only. For requirements for rigid frames with ceramic tile lining, see Section 8.4.6.
9-3WORK:V:BDM3
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BRIDGE DESIGN MANUAL Criteria Substructure Design 9.4
Retaining Walls
9.4.1
General
Retaining Walls
A retaining wall is a structure built to provide lateral support for a mass of earth or other material, the top of which is at a higher elevation than the earth or rock in front of the wall. Retaining walls depend either on their own weight or on their own weight plus an additional weight of the laterally supported material, or on a tieback system for their stability. All retaining walls not covered under Standard Walls or Preapproved Proprietary Walls are designed in the Bridge and Structures Division. The Hydraulics Section should be consulted for any walls that could be threatened by flood water or are located in a flood plain. The Architectural Section should review architectural features and visual impacts at the Preliminary Design stage. For illustrations of different types of walls, see Figures 9.4.2-1 through 9.4.2-4 at the end of this section.
9.4.2
Common Types of Walls A. Cantilevered Walls Cantilevered walls are reinforced concrete walls consisting of a base slab footing from which a vertical stem wall extends. These walls are suitable for heights up to 35 feet. Details for construction are given in the Standard Plans, along with design criteria. For nonstandard designs, the computer program RETWAL can be used for analysis. The major disadvantage of these walls is the low tolerance to post-construction settlement, which may require use of piling to provide adequate support. B. Counterfort Walls Counterfort walls are a type of cantilever wall which have ribs on the backside to strengthen the junction between footing and stem wall. These walls can exceed heights of 50 feet and generally become economical for walls having considerable portions exceeding heights of 25 feet. C. Gravity Walls Gravity walls can be made from many different materials including plain concrete, rubble masonry, mortar rubble masonry and gabions. Gravity walls depend on their own weight for stability. They are generally used for wall heights of 10 feet or less, with the exception of gabion walls, which can exceed 30 feet in height. 1.
Mortar Rubble Masonry Walls Basic design and construction standards for these walls are given in the Standard Plans. Use of masonry walls are quite limited due to the excessive cost of placing the material by hand. They are primarily used when it is necessary to blend with previously completed projects where a masonry wall already exists.
2.
Gabion Walls Gabion walls consist of wire baskets laced together and filled with rock. These walls are flexible and some post-construction settlement can be tolerated. Details for gabion wall construction are found in the Standard Plans and Specifications.
D. Cribbing Cribbing is made of metal bins, precast reinforced concrete or logs. Cribbing height is generally 10 to 30 feet.
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BRIDGE DESIGN MANUAL Criteria Substructure Design 1.
Retaining Walls
Metal Cribbing There are two types of metal cribbing approved for use in the state of Washington. The details are shown in the Standard Plans.
2.
Reinforced Concrete Cribbing Concrete cribbing is similar to metal and can be used as an alternate. It is recommended to use this type in marine areas for its ability to withstand corrosion.
3.
Log Cribbing Log cribbing has a rustic aesthetic value which makes it popular for use in locations having a natural environment, such as parks, national forests, or primitive areas. It is well suited for use on detours or temporary walls used for stage construction.
E. Cylinder Pile Walls This wall utilizes a large diameter, 4 to 10 feet, drilled shaft filled with Class 4000 concrete. The shaft is reinforced with steel beams or steel reinforcing bars. Wall heights, up to 50 feet, have been built to retain fills. Wall panels made of cast-in-place concrete, precast concrete or timber are connected to cylinder piles. F. Tieback Walls Tieback walls use vertical main load carrying members, such as soldier piles, cylinder piles, sheet piles, or slurry walls, to resist horizontal forces. The main members are connected to high strength steel bars or strand anchors, which are fixed into soil or rock with high strength grout and stressed to counteract the horizontal earth pressure loads. These walls can be built to heights exceeding 50 feet. The anchors can be incorporated into a permanent wall by the use of a double corrosion protection system or can be used in a temporary condition for shoring and cribbing. The greatest advantage in using tiebacks is that it causes minimal disturbance to the soil behind the wall and any structures resting on this soil. Nonstressed anchors, called deadman anchors, rely on passive pressure of the soil in front of the deadman panel to resist horizontal forces. G. Proprietary Walls A wall specified to be supplied from a single source (patented, trademark, or copyright) is a proprietary wall. These walls can range in heights from 15 to 50 feet. The following is a description of the most common types of proprietary walls: 1.
Structural Earth Walls A structural earth wall is a flexible system consisting of concrete face panels that are held rigidly into place with thin galvanized steel or aluminum strips extending into a select backfill mass. These walls will allow for some settlement and are best used for fill sections. The walls have three principal elements: • The backfill or wall mass: a grandular soil with good internal friction (gravel borrow). • The reinforcing metal strips, steel mesh, welded wire, or geotextiles. • The facing: precast concrete panels, welded wire with vegetation, geotextiles, or shotcrete.
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Retaining Walls
There are several important factors when selecting a structural earth wall. These are as follows: a.
Height In fills more than 10 feet high, structural earth walls are generally less costly than other wall types in fill locations.
b.
Length Adequate room is needed for earthwork equipment. Short, low walls should be avoided.
c.
Backfill A granular soil meeting the requirements of gravel borrow is required for the wall mass. In areas where the wall may become saturated, the backfill shall be free-draining. The Materials Lab will supply the Special Provisions for the wall mass material.
d.
Excavation Structural earth walls are typically more costly than other wall types in excavation areas. Greater excavation is needed to accommodate the wall mass which has a width of about 70 percent of the wall height.
e.
Foundation These walls perform well in settlement sensitive areas, but are not adaptable to pile support.
f.
Aesthetics Facing is available in a variety of surface textures, shapes and colors. Welded wire wall surfaces may have vegetation growing on exposed surfaces to match existing terrain. The backfill used in this case must be suitable to sustain vegetation growth at the face of the wall.
2.
Geotextile Walls Geotextile walls are structural earth walls that use geotextile fabric for the reinforcement and the facing. The main use of fabric walls is for temporary walls, which can become permanent walls with a cast-in-place or shotcrete facing. The Materials Lab is responsible for the design and review of geotextile walls.
3.
Other Proprietary Walls Other wall systems similar in concept to the standard crib, bin, precast cantilever, or tieback can offer cost reductions, reduce construction time, and provide special aesthetic features. A list of preapproved proprietary walls is on file in our office, including height limitations. The district can select a particular wall type from the list and include it in the contract plans, as an alternate to a Standard Wall. The Materials Lab and the Preliminary Plans Unit will approve the concept prior to Ad. The Special Provisions will be written by the Bridge Office with design criteria, and the Materials Lab will give the soil criteria needed for design and check the soil for overall stability. Prior to wall construction, the supplier will submit design calculations and shop drawings for approval. The following is a list of the proprietary wall systems that are preapproved: a.
January 1991
Criblock Retaining Walls Northwest Inc. — “Criblock” up to 30 feet.
9.4 - 3
BRIDGE DESIGN MANUAL Criteria Substructure Design b.
Retaining Walls
Hilfiker Retaining Walls, a cast-in-place concrete face is not allowed with these wall systems. (1) “Reinforced Soil Wall” — up to 30 feet. (2) “Welded Wire Wall” — up to 20 feet.
c.
The Reinforced Earth Co. — “Reinforced Earth” — up to 30 feet.
d.
VSL Corporation — “Reinforced Earth” — up to 30 feet.
H. Slurry Walls Slurry wall construction method enables wall placement to precede wall excavation. This is useful when restricted by tight right-of-way, staging construction, or where ground water is a problem. A trench is excavated for the wall and simultaneously filled with a bentonite slurry. The bentonite slurry restricts the ground water flow and holds the trench sides in place. Reinforcing steel is placed in the slurry-filled trench and concrete is placed by means of a tremie or a concrete pump while displacing the slurry. After the concrete has cured, the excavation can be completed. With the addition of tiebacks, these walls can exceed heights of 50 feet. For an aesthetically pleasing appearance, facing is used in the form of precast panels, cast-in-place concrete, or shotcrete. I.
Rock Walls Rock walls are gravity walls made of stacked large rock. They are used primarily in cut sections to provide erosion protection and limited support. They are generally 15 feet or less in height.
J.
Soil Nailing Soil nailing is a technique used to stabilize moving earth, such as a landslide, or as a means of temporary shoring. Soil anchors are used along with the strength of the soil to provide stability. The Materials Lab will design the system of soil nailing to be incorporated in the bridge contract plans.
K. Wingwall A wingwall retains the fill beyond the bridge end. It acts like a horizontal cantilevered wall with its main support from the end abutment. The two Office Standards lengths are 15 feet with 1 3/4:1 and 2:1 fill slope and 20 feet with 2:1 fill slope wingwalls. The standards also show different surface treatments, e.g., fractured fin finish or plain concrete finish. A separate design is required when using a nonstandard length. See Design Example 9.4 B1-10 for curtain wall rigidly attached to footing and abutment wall. L. Noise Walls Noise walls are primarily used in urban or residential areas to mitigate noise or to obstruct view of roadway. Precast wall panels supported by precast pilasters, cast-in-place wall and footing, or wood fencing are the common types. The Architectural Section is responsible for determining wall type. Design criteria for noise walls is based on AASHTO’s Guide Specifications for Structural Design of Sound Barriers.
9.4.3
Design A. General Refer to AASHTO Specifications and Bridge Design Manual Criteria 9.1.2, 9.3.1F and G, and 9.5.1A2. Service Load Design is used for design of retaining walls and the loading combinations shall be as described in AASHTO. Service Load Design is used rather than Load Factor Design, because of its long history of good performance and due to the lack of development of Load Factor Design criteria for retaining walls.
9.4 - 4
April 1991
BRIDGE DESIGN MANUAL Criteria Substructure Design
January 1991
Retaining Walls
9.4 - 5
BRIDGE DESIGN MANUAL Criteria Substructure Design
9.4 - 6
Retaining Walls
BRIDGE DESIGN MANUAL Criteria Substructure Design
January 1991
Retaining Walls
9.4 - 7
BRIDGE DESIGN MANUAL Criteria Substructure Design
9.4 - 8
Retaining Walls
BRIDGE DESIGN MANUAL Criteria Substructure Design
Retaining Walls
B. Cantilever Walls In general, concrete for retaining walls shall be Class 3000 Concrete with a 28-day compressive strength of 3,000 psi. For special retaining wall design, the use of Class 4000 is appropriate. Earth pressures shall be based on soil weight = 120 lb./cu. ft., the surcharge slope, the coefficient of internal friction and/or the cohesion of the backfill material. Normally the earth pressure is taken as 30 lb./cu. ft. equivalent fluid pressure when well draining granular backfill material is used. Special consideration should be given to the design of the “U” shape abutment without expansion joints between the abutment and retaining walls. At the junction of the abutment and retaining wall an equivalent fluid pressure of 45 lb./cu. ft. shall be used. This increased loading can normally be reduced to 30 lb./cu. ft. at a distance from the junction of the abutment and retaining wall equal to the average height of the wall under design. The resultant for Group I loadings (except for walls with traffic barriers having a height (H) of 16 feet or less, see table below) shall be kept within the middle one-third of footing. This can be expressed as a minimum Factor of Safety (FS) of two against overturning about the toe of the footing for spread footings or the front row of piles for pile footings (see 9.5.1 for additional criteria regarding pile footings). For all other loading combinations, the resultant shall be kept within the middle one-half of the footing. To maintain adequate safety against sliding, the following should be observed for spread footings. (FS)P (P = total horizontal force on wall) ≤ 0.5 W (W= total minimum vertical load) For walls having a height (H) of 16 feet or less, the controlling load is the 10 kip collision load. This load occurs occasionally and will have a reduced factor of safety. Wall Height, H
Overturning*
Sliding
Roadway Grade to Bottom of Footing
M abt. toe resist M abt. toe loads
Location of Resultant*
FS(EP + Sur or 10k) < 0.5 Weight
H, 16 feet or less for 10K collision load
greater than 1.5
within middle 1/2 of footing
F.S. = 1.2
H, 17 feet or more for all Wall load cases
greater than 2.0
within middle 1/3 of footing
F.S. = 1.5
Earthquake Group VII All Heights
greater than 1.5
within middle 1/2 of footing
FS(EP + EQ) < 0.5 Weight FS = 1.1
Factor of Safety (FS) Table *Both cases shall be met for determining wall stability. The 10 kip collision load shall be distributed over 16 feet. This is the minimum wall length allowed for Type 2 Retaining Walls in the Standard Plans. In a special design, the distribution width shall be the smaller of wall length between expansion joints (24′-0″ max.) or 5 feet + 2H (assumes AASHTO traffic barrier distribution plus a 45 degree influence line).
October 1993
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Retaining Walls
For sliding, the passive resistance in the front of the footing may be considered if the earth is more than 2 feet deep on the top of the footing and does not slope downward away from the wall. The design soil pressure at the toe of the footing shall not exceed the allowable soil bearing capacity supplied by the Foundation Engineer. For retaining walls resting on foundation piles, refer to Bridge Design Manual Sections 9.5.1, 9.5.2, and 9.6. Mononobe-Okabe analysis in AASHTO Guide Specifications for Seismic Design of Highway Bridges shall be used as a check in the design of the wall. AASHTO article “Abutments” gives equations to calculate the earthquake forces. Reduced factors of safety are shown in the preceding table. The Mononobe-Okabe equation requires the following assumptions: • Kv = 0, vertical acceleration coefficient is zero. • Kh = A/2, A is the acceleration coefficient. • δ, angle of friction between soil and abutment i, backfill slope angle • δ = i, slip is more likely to occur within the backfill than between soil and abutment interface. The earthquake force will be in the same direction as the slope of the surface of the backfill. • β = 0, For cantilever walls, the soil fails in a vertical plane through the footing heel. This results in β = 0 for cantilever walls, regardless of wall batter. See example in Design Aid 9.4-A1 to determine earthquake load. C. Diaphragm Walls (Other names: Slurry Wall, Cut-off Wall, or Curtain Wall) The permanent diaphragm walls include cylinder or tangent pile walls, simple panel slurry walls, and T-section slurry walls. 1.
2.
9.4 - 10
Advantages of diaphragm walls are: a.
No formwork required;
b.
No lowering of the ground water table required;
c.
Can form outer wall of structures;
d.
Irregular shapes are possible;
e.
Relatively impervious in comparison with other types of walls, if dry excavation is necessary;
f.
Construction possible under adverse circumstances, such as unfavorable soils and hydrologic conditions and where other techniques may have limitations;
g.
Can be constructed to considerable depths ahead of the main excavation;
h.
Relatively free from vibrations and noise during construction.
Disadvantages of diaphragm walls are: a.
Limited local contractor experience which may result in higher bid prices or unforeseen construction problems;
b.
The disposal of used slurries in urban areas may pose special problems.
c.
Higher cost.
October 1993
BRIDGE DESIGN MANUAL Criteria Substructure Design 3.
Retaining Walls
Design Criteria a.
Class 4000 concrete is typically used. Higher strength concrete may be specified for special cases with approval of the Bridge Design Engineer.
b.
To compensate for the effects of the concrete being cast in a slurry, the assumed concrete compressive strength shall be fc = 0.85fc′. Modulus of elasticity shall be calculated from the reduced concrete strength.
c.
Use 80 percent of the allowable bond stress (i.e., increase development length by 25 percent) for deformed bars due to the thin, slippery film coating on the reinforcing steel from the slurry.
d.
Lap splices shall be 1.5 times normally specified splice length.
e.
To allow for proper placement of concrete, use the following minimum spacing: • Vertical bars at 6 inch spacing, preferably 9 inch spacing. • Horizontal bars at 12 inch spacing.
f.
Concrete cover shall be a minimum of 3 inches;
g.
The wall panel shall be a maximum of 48 inches thick for both simple and T-section diaphragm walls. The maximum panel width is limited to 8 feet for T-section and 24 feet for simple diaphragm wall. Use the same thickness for the flange and the stem of a T-section if possible.
h.
There are tree common types of analysis: (1) Factored soil strength parameters of Cm, φm, and δm with full passive coefficient KP (so-called Duncan’s method): φm = tan-1 (tanφ) F C Cm = F 2 δm = φ 3 m By reducing soil strength parameters, the length of embedment required for wall stability is used in design. An approximate correlation between depth factor and factor of safety applied to shear strength is shown as follows: Soils Good Typical Bad
Depth Factor*
Corresponding Value of F
1.2 1.3 1.4
1.15 ~ 1.17 1.25 1.29 ~ 1.36
*Conventional practice is to use a factor of safety which increases the embedded depth by 20 to 40 percent above the value required for barely stable equilibrium. The choice of depth factor is based on engineering judgment.
October 1993
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Retaining Walls
(2) Unfactored soil parameters use KP/1.5, without adding additional length. (3) Unfactored soil parameters use KP, when providing 20 ~ 40 percent additional length. i.
Soil loading due to earthquake is based on Mononobe-Okabe pseudo-static analysis (refer to Guide Specification, Commentary “Foundation and Abutment Design Requirements, FreeStanding Abutments”) KAE = KA + KAE where KAE
= the coefficient of total earthquake earth pressure
KAE
= KA (Coulomb’s static active coefficient), when θ = 0°
∆KAE = the additional dynamic load The static loads are triangularly distributed and the additional dynamic loads are uniformly distributed on the wall. It is recommended that the horizontal acceleration coefficient Kh for diaphragm walls be the value of 1.0A, which falls in between the value of 0.5A for yielding walls and 1.5A for nonyielding walls. (A = acceleration coefficient) The design seismic passive resistances represent the total resistance during earthquake. The coefficient of passive resistance can be determined from the Guide Specifications for Seismic Design of Highway Bridges. Note that if, θ = 0°, then KPE = KP
(Coulomb’s static passive coefficient)
For the submerged portion of soils, KAE and KPE shall be calculated by replacing γ with γ′. ( Kh . γ ) = tan-1 γ′ 1-Kv where γ ′ = submerged unit weight of soil Kv = vertical acceleration coefficient j.
Two different techniques can be used for design of diaphragm walls: (1) Fixed Earth Support Method — So-called “Conventional Method” (refer to USS Steel Sheet Piling Design Manual). (2) Free Earth Support Method — So-called “Simplified Method.” This method uses active earth pressure on the projecting portions of the wall, and passive pressures on the front of the wall for the entire embedded length. The required depth of embedment is determined based on: (a) Moment equilibrium about the base of the wall; (b) Overall wall and slope stability using unfactored (or peak) soil strength parameters and factor of safety ≥ 1.5; and (c) A minimum wall depth below the excavation level depending on engineering judgment or criteria from the Materials Laboratory.
9.4 - 12
October 1993
BRIDGE DESIGN MANUAL Criteria Substructure Design
Retaining Walls Due to its simplicity and accuracy, the “Free Earth Support Method” is recommended to design diaphragm walls. A computer program name “Wall” is available.
k.
The maximum deflection at the top of the wall at service load levels shall be limited to H/120 or 4 inches, whichever is less, and to about 2 inches at the base, and to about 11/2 inches at the potential deteriorated plane (or slip plane). The calculation of deflection is based on a value of n = 16 for determining modulus of elasticity of concrete used.
l.
The wall is designed based on “Ultimate Strength Design Method” (or Load Factored Design Method”). The following procedures should be used. (1) The minimum reinforcement provided shall be adequate to fulfill the requirements of AASHTO Article “Minimum Reinforcement.” (2) Find the amount of reinforcement (on a trial basis). (3) Check flexural cracking (see AASHTO Article “Distribution of Flexural Reinforcement”). (4) Calculate moment and shear capacity and check if they are larger than the applied moment and shear based on AASHTO table “Table of Coefficients γ and β.” (5) When using the equivalent (or pseudo)-static earthquake loadings and ultimate strength design methods, the section capacity, U, should be: U ≥ 1.3 (DL + βE · EP + W) or U ≥ 1.0 [DL + βE (EQ + W)] where DL = dead load of the structural element; EP = static earth pressure acting on the element (plus surcharge); EQ = earthquake earth pressure acting on the element; W = hydrostatic water pressure βE = 1.0 when using Duncan’s Method 1.3 when using Conventional Method with full KP
m. For diaphragm wall with tiebacks: (1) Recommended embedment is a minimum of at least 10 feet below the proposed excavation level. Actual embedment may be increased to provide adequate kick-out resistance through development of passive pressure or for vertical load capacity. (2) Due to soil-structure interaction, a redistribution of lateral stresses is anticipated, resulting in reduction of pressure near the center of spans between anchors, and a concentration of pressure at supports. The design of the wall with regard to moment capacity, estimate the actual moment in the walls as follows: Mactual = R · Mcalculated The value of R for clay approaches unity as the compressibility of the soil increases. The value of R for loose sand is larger than that for dense sand. The typical value of
October 1993
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Retaining Walls R for sand is recommended to be 0.8. Also, the values of R for stiff walls are larger than for flexible walls.
D. Tieback Walls 1.
Principles of Anchor Design Anchor design includes: • Evaluation of the feasibility of anchors, • Selection of an anchor system, • Estimation of anchor capacity, • Determination of unbonded length, bonded length, and • Selection of corrosion protection. The engineer should determine whether anchors can be economically used at a particular site based on the ability to install the anchors and to develop capacity. The presence of utilities or other underground facilities may govern whether anchors can be installed. The tendon may consist of bars, wires, or strands. The choice of appropriate type is usually left to the contractor but may be specified by the designer if special site conditions exist which preclude the use of certain tendon types. In general, strands and wires have advantages with respect to tensile strength, limited work areas, ease of transportation, and storage. Bars are more easily protected against corrosion, easier to stress and transfer load. A reliable estimate of the safe anchor capacity is required from the soil’s report recommendations for each project to determine the feasibility of anchoring. The capacity of each anchor shall be verified by testing. Testing shall be part of anchor installation and included in the specifications. Based on previous experience, a range of typical design values is listed as follows:
9.4 - 14
a.
Design loads between 30 and 120 tons.
b.
The anchor wall system must be analyzed to ensure long-term stability. The minimum unbonded length must be specified in the contract document, and is usually 15 feet for soil and rock anchors (longer free lengths may be required in plastic soils, consult the Geotechnical Engineer) in order to avoid unacceptable prestress losses due to creep in the steel, soil, or rock.
c.
Angle of inclination between 10 degrees and 45 degrees. A 15 degree angle is preferred to simplify grouting and minimize vertical forces imposed on the wall by the anchors. Steeper angles, up to 45 degrees, are only recommended to reach deep bearing strata or avoid existing substructures.
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Retaining Walls
The estimated ultimate load transferred from the bond length to different types of soils is listed as follows:
Soil Type
Corrected Standard Penetration No. N
Estimated Ultimate Transfer Load in Kip/ft
Sand & Gravel
Loose (4-10) Medium Compact (10-30) Compact (30-50)
10 15 20
Sand
Loose (4-10) Medium Compact (10-30) Compact (30-50)
7 10 13
Sand & Silt
Loose (4-10) Medium Compact (10-30) Compact (30-50)
5 7 9
Silt-clay mixture with minimum LL, PI, and LI restrictions, or fine micaceous sand or silt mixtures
Stiff (10-20) Hard (20-40)
2 4
The maximum allowable anchor design load in soil may be determined by multiplying the bond length by the ultimate transfer load and dividing by a safety factor of 2.5. The ultimate load transferred from the bond length to rock deposits may be estimated from the rock type in the following table.
Rock Type Granite or Basalt Dolomitic Limestone Soft Limestone Sandstone Slates and Hard Shales Soft Shales
Estimated Ultimate Transfer Load in Kip/ft 50 40 30 30 25 10
The maximum allowable anchor design load in rock may be determined by multiplying the bond length by the ultimate transfer load and dividing by a safety factor of 3.
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BRIDGE DESIGN MANUAL Criteria Substructure Design 2.
Retaining Walls
Coefficient of Earth Pressure Practically, the design should be first considered using active pressure coefficients (KA) unless structures exist within a lateral distance equal to twice the wall height. For this case, an average earth pressure coefficient (K) should be computed as follows: x K = Ko - 2H (Ko - KA) where x = H = Ko = Note:
(1)
distance from structure wall height of wall coefficient of at-rest earth pressure KA allows lower wall design pressure (if small wall displacements) can be tolerated, i.e., ground subsidence occurs. Ko increases wall design pressure but limits wall displacement, i.e., ground subsidence is limited.
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January 1991
Retaining Walls
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Retaining Walls
Typical amount of wall translation (top movement) to develop the active earth pressure. Soil and Condition
3.
Amount of Translation
Cohesionless Dense
(0.1% to 0.2%)H
Cohesionless Loose
(0.2% to 0.5%)H
Cohesive Firm
(1% to 2%)H
Cohesive Soft
(2% to 5%)H
Corrosion Protection The corrosion protection of anchors can be divided into two categories*: a.
Simple Protection The use of simple protection relies on Portland cement grout to protect the tendon, bar, or strand in the bond zone. The unbonded lengths are sheaths filled with anti-corrosion grease, heat shrink sleeves, and secondary grouting after stressing. Except for secondary grouting, the protection is usually in place prior to inserting the tendon in the hole.
b.
Double Protection Complete encapsulation of the anchor tendon is accomplished by a corrugated PVC, high-density polyethlene, or steel tube. The same provisions of protecting the unbonded length for simple protection are applied to those for double protection.
*Provide simple protection for temporary tieback walls (less than 18 months) and double protection for permanent tieback walls. 4.
Angle of Wall Friction The wall friction depends on the soil properties, the amount and direction of wall movement, the wall material, and the surface condition. Values of δ = 0 or δ = φ are generally too low and high, respectively, for most practical cases. The typical values are between 1 φ/3 and 2 φ/3. It is conservative if assumed δ = 0.
5.
Determination of Tieback Spacing The preliminary anchor spacing can be determined from Figure 9.4.3-1. Suggested temporary test loads are between 75 and 80 percent of Guaranteed Ultimate Tensile Strength (GUTS). Suggested Limits for design loads, T, are between 0.5 and 0.6 of GUTS (typically 53 percent). Therefore, (S1 + S1)S2 = T cos q 2 PE Typical pile spacings (horizontal) of 6 to 10 feet and anchor spacings (vertical) of 8 to 12 feet are commonly used. The minimum spacing of 4 feet in both directions is not recommended for considering the effectiveness and disturbance of anchors due to installation.
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January 1991
Retaining Walls
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BRIDGE DESIGN MANUAL Criteria Substructure Design 6.
Retaining Walls
Design of Soldier Pile Tieback Walls a.
Lateral Earth Pressures Case 1
Cantilever Soldier Piles and Piles with Single Level Tieback
Figure 9.4.3-2 For the submerged portion of soil, KAE and KPE should be calculated by replacing θ with θ′ in Equations (4) and (5) and replacing γ with γ′ for calculating earth pressure.
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Note: (1) Neglect any passive resistance below the base of excavation in D zone where D is the largest value of 1.5 times shaft diameter, 0.1 times height of the wall, depth of fascia wall footing, or anticipated future excavation depth within 20 feet of wall. (2) Active pressure is assumed to act over pile spacing above base of excavation and over shaft diameter below base of excavation. Passive pressure is assumed to act over two times over shaft diameter or pile spacing, whichever is smaller. (3) For permanent tiebacks, tie back DESIGN LOAD, T, Shall be (1) + (2) or [(1) + (3)]/1.5, whichever is greater. For temporary tiebacks, tie back DESIGN LOAD, T, shall be (1) + (2). (4) Lock-off load is 80 percent of (1) + (2) for permanent wall and 70 percent of (1) + (2) for temporary wall. (5) Proof test to 1.5T for permanent tiebacks and to 1.3T for temporary tiebacks.
July 1996
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BRIDGE DESIGN MANUAL Criteria Substructure Design Case 2
Retaining Walls Multiple Level Tieback
Figure 9.4.3-3
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BRIDGE DESIGN MANUAL Criteria Substructure Design b.
Retaining Walls
Depth of Embedment For cantilever piles without tieback, the embedment should be determined to satisfy horizontal force equilibrium and moment equilibrium about the bottom of the pile. For piles with tiebacks, the depth of embedment is determined by moment equilibrium of lateral force about kpoint 0. Neglect the moment resistance of soldier pile member at 0. Depth of embedment, D, must also be sufficient to provide necessary vertical capacity or adequate kick-out resistance through development of passive pressure.
c.
Design of Timber Lagging Most commonly, the lagging thickness is determined from past construction experience as related to depth of excavation, soil condition, and soldier pile spacing. In other cases, soil pressure distribution recommended by geotechnical engineer is used to determine the thickness of lagging. The soil pressure distribution equal to 50 percent of the lateral earth pressure diagram is recommended to design lagging which is simply supported. The 50 percent reduction is due to the soil arching effect behind the wall. However, this procedure leads to unreasonably thick lagging for deep excavations with relatively larger soldier pile spacings.
d.
Design of Fascia Wall Fascia wall shall be reinforced concrete and shall be designed according to the latest AASHTO Standard and Interim Specifications for Highway Bridges.* The minimum structural thickness of fascia wall shall be 9 inches. Architectural treatment of facing shall be indicated on the drawing. Concrete strength shall not be less than 3,000 psi at 28 days. The wall is to extend 2 feet minimum below the ground line adjacent to the wall. Permanent drainage systems shall be provided to prevent hydrostatic pressures developing behind the wall. A cut which slopes toward the proposed wall will invariably encounter natural subsurface drainage. Vertical chimney drains, prefabricated drains, or porous engineering fabrics can be used for normal situations to collect and transport drainage to a weep hole or pipe located at the base of the wall. Concentrated areas of subsurface drainage may be controlled by installing horizontal drains to intercept the flow at a distance well behind the wall. *Note: (1) Most possibilities of load cases governing are: Group I = 1.3(DL + 1.67LL + 1.3E) Group VII = 1.0(D + E + EQ) (2) 50 percent of worse load is used for design. (3) Check for 10 kips impact load.
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Retaining Walls
e. Design of Soldier Piles The soldier piles shall be designed for shear, bending, and axial stresses, and according to the latest AASHTO design criteria. Soldier piles may be steel or concrete with a minimum yield strength of steel being 36 ksi or the minimum strength of concrete shall be 4,000 psi at 28 days (concrete Class 4000). Due to soil-structure interaction, a redistribution of lateral stresses is anticipated, resulting in a reduction of pressure near the center of spans between anchors and a concentration of pressure at supports. The actual bending moment is recommended to be 80 percent of the maximum bending moment calculated based on the free-earth method. f.
Check for Stage Construction The earth pressure distribution for an anchored wall changes during wall installation. The procedures for checking the stability of the wall system for temporary construction loadings are described as follows: (1) Draw “pressure diagrams” at various construction stages, each including all pertinent loads, i.e., surcharge, water, soil, etc. (a) A triangular diagram for estimating cantilever excavation to first anchor or for walls with only one anchor row. (b) A trapezoidal diagram for temporary excavation below first anchor level. (c) A trapezoidal diagram for final depth excavation. (2) Find preliminary anchor spacing. (a) First anchor row Determine the safe cantilever or unsupported excavation height. Assume the first anchor row is located 3 feet above this level. This distance is required for anchor installation. Find lateral spacing by dividing anchor allowable capacity by area of pressure diagram in step 1c. (b) Subsequent excavation levels must consider increased loads on previous anchor rows. Necessary embedment of soldier piles must be considered at all stages of excavation. Diameter of shaft may be increased to reduce penetration. (3) Estimate required section modulus of soldier piles at all stages of excavation to ensure structural integrity. Adjust anchor spacing to optimize structural design. (4) Estimate the permanent vertical loads due to anchor inclination and wall dead weight and check: (a) vertical member structural capacity, (b) bearing capacity of the soil/rock, and (c) settlement. (5) Check overall stability of final design.
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Retaining Walls
(6) Construction checks during design: (a) Size anchor tendon structurally to resist maximum prescribed test load at less than 80 percent of ultimate strength. (b) Determine the maximum transfer load for the upper anchor row based on allowable passive resistance (KP/1.5) at that initial wall height. g.
Design of Bond Length The bond length should not be specified in the contract plan. For design purposes, the required bond length can be approximated with sufficient accuracy as discussed in other parts of this section to permit cost estimates and right of way acquisitions to be made confidently. The bond transfer values for soil grout length (or bond length) should be verified by testing to determine the required bond length. Some important points are listed as follows: (1) A minimum bond length should be specified in the contract documents. The recommended values are 10 feet in rock and 15 feet in soils. (2) The bond lengths exceeding 40 feet in soils or 254 feet in rock do not efficiently increase the anchor capacity. (3) At sites with restricted right of way, the maximum bond length is the distance from the end of unbonded length to within 2 feet of the right of way. (4) To permit high pressure grouting without damage to existing facilities and to ensure adequate overburden pressure to mobilize the full friction between soil and grout, a 15-foot minimum overburden cover over the bond zone is recommended for anchors of average capacity (i.e., 150 kips or less). (5) Anchors founded in mixed ground condition should be designed assuming the entire embedment is the weakest deposit. (6) The bar or strand grout length (or bar bond length) is 15 feet.
July 1996
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BRIDGE DESIGN MANUAL Criteria Substructure Design h.
Retaining Walls
Recommended Tieback Wall Configuration (1) Base of excavation larger than 10 feet above soft soil layer.
Figure 9.4.3-4a
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Retaining Walls
(2) Base of excavation in or smaller than 10 feet above soft soil layer.
Figure 9.4.3-4b Note: Stability number n and m are determined based on stability analysis of the project walls. Consult with Material Laboratory to obtain appropriate values of n and m.
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Retaining Walls
(3) Typical section of solider pile tieback wall.
Figures 9.4.3-5
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BRIDGE DESIGN MANUAL Criteria Substructure Design 9.4.4
Retaining Walls
Miscellaneous Items A. Drainage All concrete retaining walls shall have 3-inch diameter weepholes located 6 inches above final ground line and spaced about 12 feet apart. In case the vertical distance between the top of the footing and final ground line is greater than 10 feet, additional weepholes shall be provided 6 inches above the top of the footing. No weepholes are necessary in cantilever wingwalls. Drainage features shall be detailed on plans. Weepholes can get clogged up or freeze up, and the water pressure behind the wall may start to build up. In order to keep the water pressure from building up, it is important to have well draining gravel backfill and underdrains. Appropriate details must be shown on the plans. No under drain pipe or gravel backfill for drains is necessary behind cantilever wingwalls. A 3-foot thickness of gravel backfill shall be shown on the plan behind the cantilever wingwalls. Backfill material shall not be a part of bridge quantities. If it is necessary to excavate existing material for the backfill, then this excavation shall be a part of Structural Excavation Class A of bridge quantities. B. Joints For cantilevered and gravity walls, joint spacing should be a maximum of 24 feet on centers. For counterfort walls, joint spacing should be a maximum of 32 feet on centers. For tieback wall, joint spacing should be 24-32 feet on centers for cast-in-place walls, but for precast units, the length of the unit would depend on the height and weight of the unit. Odd panels for all types of walls shall normally be made up at the ends of the walls. Every joint in the wall shall provide for expansion. For cast-in-place construction, a minimum of 1/2 inch premolded filler should be specified. A compressible back-up strip of closed-cell foam polyethylene or butyl rubber with a sealant on the front face is used for precast concrete walls. No joints other than construction joints shall be used in footings except at bridge abutments and where the change from a pile footing to a spread footing occurs. In these cases, the footing shall be interrupted by a 1/2 inch premolded expansion joint through both the footing and the wall. The maximum spacing of construction joints in the footing shall be 120 feet. The footing construction joints should have a minimum 6-inch offset with the expansion joints in the wall. C. Architectural Treatment The type of face treatment for retaining walls is decided on a job-to-job basis according to degree of visual impact. It should be discussed with the Bridge Architect at the time of preliminary plan preparation. The wall should blend in with its surroundings and complement other structures in the vicinity. Top of walls are usually smooth flowing curves as seen in elevation. See Retaining Wall Standard Sheets for top of wall and ground line relationship and also for cambering of front of cantilevered retaining walls.
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Retaining Walls
D. Concrete Fill for Soldier Pile Walls 1.
Soldier Pile Walls With No Tieback Anchors For this type of soldier pile wall, use lean concrete for the entire soldier pile embedment length. For a wet hole, use a special designed lean concrete. Typically, the contractor designs and submits this special design lean concrete for approval.
2.
Soldier Pile Walls With Tieback Anchors For this type of soldier pile wall, use lean concrete for the portion of the soldier pile above final grade (above the cut line in front of the soldier pile wall). Below final grade, where transfer of load for the vertical component of the sloping tieback(s) is resisted, use concrete Class 4000P. Concrete Class 4000P is permissible in a wet hole (placed by tremie).
E. Detailing of Standard Reinforced Concrete Retaining Walls 1.
In general, the “H” dimension shown on retaining wall plans should be in foot increments. Use the actual design “H” reduced to the next lower even foot for dimensions up to 3 inches higher than the even foot. Examples:
Actual height ≤ 15′-3″, show “H” = 15 on design plans Actual height > 15′-3″, show “H” = 16 on design plans
For walls which are not of a uniform height, “H” should be shown for each segment of the wall between expansion joints or at some other convenient location. On walls with a steep slope or vertical curves, it may be desirable to show 2 or 3 different “H” dimensions within a particular segment. The horizontal distance should be shown between changes in the “H” dimensions. The value for “H” shall be shown in a block in the center of the panel or segment. See Example, Figure 9.4.4-1. 2.
Follow the example format shown in Figure 9.4.4-1.
3.
Calculate approximate quantities using the Standard Plans.
4.
Wall dimensions shall be determined by the designer using the Standard Plans.
5.
Do not show any details given in the Standard Plans.
6.
Note on the plans any deviation from the Standard Plans.
7.
Do not detail reinforcing steel, unless it deviates from the Standard Plans.
8.
For pile footings, use the example format except revise the footing size, detail any additional steel, and show pile locations.
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Footings
9.5
Footings
9.5.1
Spread Footings A. General The provisions given in this section pertain to both spread footings and pile supported footings except as noted in 9.5.2, Pile Supported Footings. 1.
Footing Shape and Location Footings shall normally be rectangular in plan for both square and skewed bridges. Footing depth will normally be set at the minimum required to assure adequate bearing pressure and cover. On stream crossings, additional cover depth may be required as protection against scour. The Hydraulic Section should be consulted on this matter. Unnecessary footing depth results in large increases in cost. The end slope on the bridge approach fill is usually set at the preliminary plan stage but affects the depth of footings placed in the fill. Figure 9.5.1-1 illustrates some items to consider when developing footing positions.
2.
Retaining Wall Footings Retaining wall footings shall be designed using working stress methods for reasons stated in Subsection 9.4. The resultant of forces shall be kept within the middle one-third of the footing for Group I loadings and within the middle one-half of the footing for all other service load conditions, including impact collision load for walls under 16 feet. See AASHTO Working Strength Loading Combinations.
3.
Design Loadings for Spread or Pile Footings Footings will normally be designed by load factor methods. The factored loads shall be in accordance with Section 4, as modified below. Where the footing is being used to support a long column, the magnified moments shall be used for footing design. See Section 9.2.1E for guidance on computing magnified moments. See Figures 9.5.1-2 and 9.5.1-3 for modes of failure for spread and pile footings. Allowable soil bearing capacities and pile loads are given in terms of service loads as they are obtained from the Foundation Engineer or, in the case of piles, specified on the plans. When factored loads are applied to the footing, the following maximum soil or pile loading shall apply. This value includes any capacity reduction φ factor. a.
Basic Load Combination Using Group I Working Stress Design, the soil or pile loading shall not exceed 1.0 times the allowable, and for spread footings, the resultant shall fall within the middle one-third of the footing area. In the case of a pile footing: (1) No uplift shall be used for Group I loading. (2) Stability requirements shall be met without mobilizing the piles. (3) Stability check against overturning shall be taken about the front row of piles.
b.
Factored Load Combinations (1) Soil Pressure or Pile Reactions For any factored load combination, the soil loading shall not exceed twice the allowable. Maximum pile loading shall be in accordance with the following:
October 1993
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Footings
Guidelines for Footing Location Figure 9.5.1-1
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October 1993
BRIDGE DESIGN MANUAL Criteria Substructure Design
Footings
Modes of Failure for Spread Footings Figure 9.5.1-2
October 1993
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Footings
Modes of Failure for Pile Footings Figure 9.5.1-3
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Footings Groups I-IV, 1.5 x allowable pile bearing capacity Groups V-IX, 1.75 x allowable pile bearing capacity Soil pressure or pile reaction is computed considering that it is not possible to develop any tension between the footing and the soil or pile below. In some special cases, tension in piles may be allowed as explained in Section 9.6.2B2.
c.
Stability Load Combination The following criteria have been developed for design of footings for stability: When dead load tends to increase stability, use βD = 0.75 in the AASHTO Load Factor Combinations. The resultant shall fall within the middle two-thirds (or uplift on not more than one-half of the area of the footing or one-half of the piles).
d.
Sliding An adequate factor of safety against sliding based on factored loads shall be maintained under all conditions. Defining Pu as the total minimum factored vertical load on the footing and Hu as the total factored horizontal load on the footing, the ratio between these values shall be such that: 1.1 Hu ≤ 0.5 Pu
B. Load Distribution Under Footings 1.
Force Distribution A straight line force distribution shall be assumed for resisting forces. Where appropriate, a suitable “bi-axial” analysis shall be used which accounts for the shape of the actual positive pressure area under the footing. Design Aid sheet 9-5A-1 “Stress on a Rectangular Footing, Normal Load Outside Kern” can be used to calculate true soil pressures. The “Bi-Axial Stress Analysis” computer program will also compute this condition. Negative footing reactions will not be allowed except in the case of friction piles with appropriate reinforcement provided at the connection between the pile and the footing. See 9.5.2.
2.
Footings With Seals For establishment of seal size for footings with seals, see 9.7. The footing size shall normally be set as 2′- 0″ less than seal size in rectangular dimensions. Where there is a good possibility that the seal may be eliminated at the time of construction, an alternate footing design with no seals should be detailed on the plans. See Section 9.7 for method of establishing footing elevation in this case.
C. Pedestals A pedestal is sometimes used as an extension of the footing in order to provide additional depth for shear near the column. Its purpose is to provide adequate structural depth while saving concrete. For proportions of pedestals, see Figure 9.5.1-5. Since additional forming is required to construct pedestals, careful thought must be given to the trade off between the cost of the extra forming involved and the cost of additional footing concrete. Also, additional foundation depth may be needed for footing cover.
October 1993
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Footings
Whenever a pedestal is used, the plans shall note that a construction joint will be permitted between the pedestal and the footing. This construction joint should be indicated as a construction joint with roughened surface. D. Footing Design 1.
Footing Thickness and Shear Design The minimum footing thickness shall be 1 foot 6 inches or, for pile supported footings, 2 feet 0 inches. The minimum plan dimension shall be 4 feet 0 inches. Footing thickness may be governed by the development length of the column dowels, or by concrete shear requirements, with or without reinforcement. If concrete shear governs the thickness, it is the Engineer’s judgment, based on economics, as to whether to use a thick footing unreinforced for shear or a thinner footing with shear reinforcement. Generally, shear reinforcement should be avoided but not at excessive cost in concrete, excavation, and shoring requirements. Where stirrups are required, place the first stirrup at d/2 from the face of the column or pedestal. For large footings, consider discontinuing the stirrups at the point where vu = vc. For proportions of footings and pedestals and footings on rock, see Figure 9.5.1-5. Shear strength requirements are stated in AASHTO Specifications. They are summarized in Figure 9.5.1-4.
2.
Reinforcement a.
Column Dowels Column dowels shall be anchored into the footing in such a manner as to adequately transfer loads to the footing. Column dowels shall be hooked in order to facilitate placing, prevent their insertion into wet concrete, and to minimize footing thickness. Bars in tension shall be developed using length, 1.25 Lb, as shown in Chapter 5 of this manual. Bars in compression shall develop a length, 1.25 Ld, prior to the bend, as shown on Sheet 5-164. Where bars are not fully stressed, lengths may be reduced in proportion, but shall not be less than 3/4 Ld. The concrete strength used to compute development length of the bar in the footing shall be the strength of the concrete in the footing. The concrete strength to be used to compute the section strength at the interface between footing and column concrete shall be that of the column concrete. This can be allowed because of the confinement effect of the wider footing.
b.
Bottom Reinforcement Reinforcement shall be designed in accordance with AASHTO provisions and current office practice shown on Figure 9.5.1-4. However, reinforcement shall not be less than #6 bars at 12-inch centers to account for uneven soil conditions and shrinkage stresses.
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January 1991
Footings
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BRIDGE DESIGN MANUAL Criteria Substructure Design
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Footings
BRIDGE DESIGN MANUAL Criteria Substructure Design c.
Footings
Top Reinforcement Top reinforcement shall be used in any case where tension forces in the top of the footing are developed. Where columns and bearing walls are connected to the superstructure, sufficient reinforcement shall be provided in the tops of footings to carry the weight of the footing and overburden assuming zero pressure under the footing. This is the uplift earthquake condition described under “Superstructure Loads.” This assumes that the strength of the connection to the superstructure will carry such load. Where the connection to the superstructure will not support the weight of the substructure and overburden, the strength of the connection may be used as the limiting value for determining top reinforcement. For these conditions, the AASHTO requirement for minimum percentage of reinforcement will be waived. Regardless of whether or not the columns and bearing walls are connected to the superstructure, a mat of reinforcement shall normally be provided at the tops of footings. On short stub abutment walls (4 feet from girder seat to top of footing), these bars may be omitted. In this case, any tension at the top of the footing, due to the weight of the small overburden, must be taken by the concrete in tension. Top reinforcement for column or bearing wall footings designed for two-way action shall not be less than #6 bars at 12-inch centers, in each direction while top reinforcement for bearing wall footings designed for one-way action shall not be less than #5 bars at 12-inch centers in each direction.
9.5.2
Pile Supported Footings A. General Requirements Design of pile footings shall follow the general requirements set forth in 9.5.1 for spread footings. Steel H-Pile or timber piles shall be embedded a minimum of 12 inches into the footing where a moment or tension connection is not required. Cast-in-place concrete piles with reinforcing extending into footings shall be embedded a minimum of 6 inches. There shall be 11/2 inches of clearance between the bottom mat of footing reinforcement and the top of pile (see Figure 9.5.2.1). In determining the proportion of pile load to be used for calculation of shear stress on the footing, any pile with its center 6 inches or more outside the critical section shall be taken as fully acting on that section. Any pile with its center 6 inches or more inside the critical section shall be taken as not acting for that section. For locations between, the pile load acting shall be proportioned between these two extremes. For calculation of moment on the footing, any pile with its center outside of the section shall be taken at full load. Any pile with its center inside of the section shall not be assumed to contribute to that amount. All piles shall have an embedment in the soil sufficient to resist lateral forces and develop axial loads. B. Pile Spacings Generalized pile spacings are shown in Section 9.6 for each type of pile. Be aware that the action of the pile group for friction piles may be quite different than for point bearing piles, in that the group can fail as a unit at a lower load than the summation of the individual pile capacities. This effect is accounted for in Chapter 4, “Modeling Pile Foundation.” For point bearing piles, the spacing is a minimum of 3 feet, except for timber piles where the minimum spacing is 3 feet 3 inches. Where the load distribution of the pile is partially point bearing and partially friction, consider using an intermediate spacing value. Distance from center of pile to footing edge for all pile types shall be a maximum of 1.5 times the pile diameter or 1 foot 6 inches.
April 1993
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BRIDGE DESIGN MANUAL Criteria Substructure Design
Footings
Typical Pile Footing Reinforcing Placement Figure 9.5.2-1 C. Horizontal Force on Pile Groups Piles resist horizontal forces by a combination of internal strength and the passive pressure resistance of the surrounding soil. The pile is modeled like a beam on an elastic foundation or by the use of computer programs, i.e., LPILE1. LPILE1 requires soil properties supplied from the Materials Lab in order to generate P-Y curves. P-Y curves represent the force required to deflect a pile a unit length. Forces and moments are applied to the pile and LPILE1 calculates the deflections along its length. The results can also be used to determine pile lateral and rotational springs. For more information on modeling individual piles or pile groups, see Chapter 4 “Foundation Modeling.” D. Uplift Forces When piles are subject to uplifting forces or a “built in” condition is needed at the top of the pile, the pile must be adequately connected to the footing by means of extended reinforcement, welded bars, or other means. No uplift capacity is allowed due to the bond between pile and embedment into footing. Uplift pile capacities shall be determined by Materials Lab. Construction methods used for jetted or spudded piles reduce uplift capacity.
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Piles and Piling
9.6
Piles and Piling
9.6.1
General Considerations A. Selection of Pile Type Piles should not be used where spread footings can be used at allowable basic bearing pressures of approximately 2 to 3 ton/sq. ft. or greater. Where heavy scour conditions may occur, pile foundations should be considered in lieu of spread footings. Where large amounts of excavation may be necessary to place a spread footing, pile support may be more economical. The following is a general summary of comparative pile properties.
Pile Type
Penetrat. ofHard Strata
Laetral Force Resist.
Ease of Splice
Moderate
High.
High
Cost
Capacity
Steel HP
High
High
Conc.
Moderate
Moderate
Moderate (CIPGood) w/tip
Moderate
Good
High
CIPHigh Precast Low
Timber
Low
Low
Poor
Moderate
Poor
Low
Low
Cylinder
High
Very High
Good
Moderate
Moderate
Very High
Precast Low
Very Good
Frci toi n
Easeof Connect. toStruct.
High
B. Friction vs. Point Bearing Piles Piles may be of friction type or point bearing or a combination of both. AASHTO “Load Capacity of Piles” shall pertain for the design of piling, except as noted herein. Normally in the absence of a soil layer which can offer adequate resistance to develop full point bearing, the pile shall be considered to be acting as a friction pile. The Materials Laboratory will provide information as to the ability of the soil to support the pile load. The conditions of support of the pile in the soil may affect several structural properties. These may be: rate of pile elastic shortening, effect of group action and hence spacing, column stability of the pile, and ability to resist lateral forces. C. Pile Loads and Spacings The loads allowed and spacing of piles in groups are usually as tabulated below. Many other combinations are possible; however, their use should be predicated on suitable analysis and concurrence of the Bridge Design Engineer and the Foundation Engineer. Pile selection shall be made to give maximum economy combined with adequate load capacity and ability of the pile to be driven into the particular material.
January 1991
9.6 - 1
BRIDGE DESIGN MANUAL Criteria Substructure Design
Capacity*
Piles and Piling
Peli Materail
Spacingof FrictionPiles
‡
Spacingof PointBearing Pelis
Edge Distance**
PileSize
40 T
Timber
3′-3 ″
3′-3 ″
1′-6 ″
Spec.
55 T
Concrete Steel
4′-0 ″
3′-0 ″
1′-6 ″
† » HP 12 x 53
70 T
Concrete Steel
4′-6 ″ 4′-6 ″
3′-3 ″ 3′-3 ″
1′-9 ″ 1′-6 ″
+ HP 12 x 53
Table 9.6.1B August 1974 » 10 BP 42 may be used if the pile is point bearing for this capacity. † 12-inch diameter min. for Concrete Filled Casing. 13-inch diameter min. for Precast or Precast Prestressed. 14-inch diameter min. Butt for Tapered. 10-inch or 12-inch Square Precast Prestressed. 12-inch diameter min. for Hollow Prestressed Spun Piles. + 14-inch diameter min. for Concrete Filled Casing. 16-inch diameter min. for Precast or Precast Prestressed. * Capacity shown is rated Basic (working) load value and includes the effect of any downdrag forces. ‡ The Converse-Labare Formula (AASHTO “Group Pile Loading”) need not be applied to pile values shown here. This formula reduces the vertical load carry capacity of a pile group. See Foundation Modeling, Chapter 4, for lateral load capacity reduction for pile groups. ** Center of pile to footing edge. The above table is a guide to usual practice and is not intended to restrict the use of other capacities and spacings where needed. Maximum pile spacings should be limited to about 10 feet. With spacings beyond this, the shear between the footing and column or wall may become a problem.
9.6.2
Design Considerations A. Column Action Consideration shall be given to the pile acting as a column. Piles which extend above the ground surface shall be analyzed by the appropriate column design procedures. Piles which are driven through very weak soils should be designed for reduced lateral support, using information from the Materials Laboratory as appropriate. Piles driven through firm material normally can be considered to be fully supported for column action (buckling not critical).
9.6 - 2
April 1993
BRIDGE DESIGN MANUAL Criteria Substructure Design
Piles and Piling
B. Uplift Capacity 1.
Introduction The ability of a pile to carry uplift loads is highly dependent upon the strata into which it is driven. Unless detailed knowledge of that strata is available at the time of design, the pile should not be relied on to carry uplift loads. In all cases where uplift loads are to be carried, the connection between the pile and the footing must be carefully detailed. The bond between the pile and the seal may be considered as contributing to the uplift resistance. This bond value shall be limited to 10 psi.
2.
Computation of Uplift Capacity Appropriate values of uplift should be those values recommended by the Materials Lab. If the information is not available, the following will give guidance on uplift capacity. Pile uplift may be considered to act to assist in carrying factored loads within the limits specified below. When pile uplift is considered to carry a portion of the factored loads, a check shall be made to ensure that no tension on the piles is necessary to carry any basic combination (factor of 1.0) of DL, LL, Wind, or Stream Flow. Where pile tension is used, it shall be computed as follows: Ro = B 50 Where B is the average blow count from the test hole log in blows/foot and Ro is the resistance of the pile surface in Ton/Ft.2, the total resistance of the pile to pull out is then Rp = Ro(1p)P where 1 is the effective pile length and P is the perimeter of the pile. Consider P to be 2 X (Flange width plus depth) for H Piles. The above computed value for Ro gives essentially an ultimate pull out value. To give usable values, use a factor of safety of 3 for working stress design on a “capacity reduction factor” of 2/3 for load factor design. Do not use more than 40 percent of the pile downward load capacity, however. For calculation, use a length of pile 5 feet shorter than minimum tip elevation.
3.
January 1991
Cautions to be Exercised with Respect to Pile Uplift a.
The pile must be a friction pile and over 10 feet in length. Whenever uplift is to be used in the design, the Foundation Engineer shall be consulted. Do not use for full point bearing piles.
b.
The tension connection between the pile and the structure must be adequate.
c.
The pile must be adequate to carry tension throughout its length. For example, a timber pile with a splice sleeve could not be used.
d.
Preboring, jetting, or spudding must not be used to aid in driving the pile and must be so noted in the plans or special provisions.
e.
The use of pile load tests to verify the uplift capacity of the piling should be considered.
9.6 - 3
BRIDGE DESIGN MANUAL Criteria Substructure Design
Piles and Piling
C. Lateral Resistance Lateral forces applied to piles must be carried either by passive soil resistance and bending or by battered piles. 1.
The capacity of the pile to carry horizontal loads should be investigated using beam on elastic foundation theory. A computer program (LPILE) is available to assist in this calculation. Soil modules can be obtained for each soil layer from the Materials Laboratory. For material such as fill compacted to specification requirements, a soil modulus value of 40 tons per cubic foot, constant variation, might be used. This means that the elastic modulus of the soil at one foot depth is 40 T/sq. ft., at 2-foot depth is 80 T/sq. ft., etc. For other types of soil, the modulus may not vary from top to bottom. The limitation on soil stress is, at the same time, 3.0 tons (working stress) per square foot. Again, some deflection (about of 0.5 inch) will usually be associated with this resistance and that deflection must be acceptable in the total design.
2.
Passive Resistance of Piles In lieu of the above analysis, a maximum passive resistance of 3 tons (ultimate capacity 6 tons) may be assumed for each foundation pile provided the footing is built directly on the soil and that the soil below the footing is capable of carrying this load. This figure is to be used for 12-inch diameter or 12-inch square piles and larger only. For 10-inch square piles, use half of this amount. For this condition, the bending in the pile is neglected and assumed to be within the capacity of the pile to resist. It should be noted that a horizontal deflection will be associated with the development of this resistance.
3.
Pile Bents Piles which support footings or pile caps that are not in contact with the soil below them, must be treated as columns, subject to bending and axial load. The calculation of lateral resistance must follow a procedure similar to the one mentioned above.
4.
Battered Piles Where passive pressures will not carry the imposed lateral loads, or where horizontal rigidity is required, battered piles must be used. The lateral force which can be resisted by a single battered piles is limited by a function of applied vertical load, and this must not be exceeded. Maximum batter shall be 41/2:12.
D. Other Considerations 1.
Driving stresses are calculated by the Materials Lab. Additional information such as recommended pile type, wall thickness, bearing stresses, etc., can be requested from their office.
2.
Elastic Settlement The effect of elastic settlement should not be used to develop factors for normal frame moment distribution. It is valuable when evaluating forces developed by deflection of piers where these forces must be carried by the structure. Actual footing rotation, due to applied loads on a pile supported footing, may be computed using the elastic shortening of the piles in the group and using the usual PL/AE equation. The problem then is to establish an appropriate L value. For fully point bearing piles, this length can be taken to be the full length to the bearing strata. For fully friction piles, half of the estimated pile length might be appropriate with intermediate lengths being used for piles which will be partially point bearing.
9.6 - 4
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design 3.
Piles and Piling
Pile Splices Pile splices shall be avoided where possible. If splices may be required in timber piling, a splice shall be detailed on the plans. Splices between treated and untreated timber shall always be located below the permanent water line. Concrete pile splices shall have the same strength as unspliced piles.
4.
Driving Considerations The conditions required for driving shall be considered in all designs. Some of the conditions are as follows: a.
Soil Character The type of soil governs the pile type and may require the use of points or shoes. Timber piles cannot ordinarily be driven through hard gravel layers, and such layers may require the use of concrete or steel piles. When cobbles, boulders, or rock fills exist at the site, a drilled pile or shaft should be used.
b.
Preboring Preboring is used when an intermediate hard layer must be penetrated in order to reach bearing layers below, when the amount of driving must be limited to avoid disturbance to buildings, or when precise placement of the piles is required. Preboring will normally be carried as a separate bid item. On widenings, driving piles through existing fills often requires spudding or jetting to assist in pile driving. These are contractor options and are not pay items. See Standard Specifications for contractor requirements.
c.
Clearances It is the designer’s responsibility to ensure that sufficient room is available for driving piling. This is a problem when working on widenings adjacent to existing structures and in urban areas. Normally 20 feet of minimum headroom is necessary. Timber piles can be driven two feet horizontally from a vertical surface, but additional clearance is desirable. Occasionally, driving the piling from the existing structure is the only alternative. In such a case, the ability of the supporting structure to support the pile driver and the dynamic forces must be analyzed and shall be noted in the Special Provisions. Access room for the driver to enter the site must be assured.
d.
Maximum Batter The batter on piles shall not exceed 41/2 to 12. Piles with batters in excess of this become very difficult to drive and the bearing values become difficult to predict. Ensure that battered piling do not intersect piling from adjacent footings within the maximum length of the piles.
e.
Pile Load Tests Pile load testing is used when doubt exists as to whether or not the driving formula actually represents the capacity of the pile. Where such tests are used, they are conducted by the Materials Laboratory. On large jobs, consideration should be given to pile load tests in the design stage in order to reduce foundation costs.
January 1991
9.6 - 5
BRIDGE DESIGN MANUAL Criteria Substructure Design f.
Piles and Piling
Estimate Pile Length Pile length quantity calculations are determined from the estimated tip elevation given in the Soils Report. A 40-ton timber pile in granular material will usually develop full load by the time it is well into a layer of 25 to 30 blow count.
9.6.3
Concrete Piles A. Specifications When concrete piles are specified, the Standard Specifications Section 6-05 allow the contractor to select the pile type, i.e., precast or cast-in-place and describes the network of construction. Reinforcement for 55- and 70-ton piles is specified in the Standard Specifications. Where bearing values are specified on the plans other than 55- and 70-ton piles, or if the standard reinforcement is inadequate for the application, the details or Special Provisions must provide for the reinforcement. The following criteria shall be used for cast-in-place concrete piles: 1.
The wall thickness will be determined by Materials Lab analysis of pile driving formula. Unless otherwise specified, the design shall be based on a steel shell thickness of 1/4 inch for piles less than 14 inches in diameter, 3/8 inches for piles 14 to 18 inches in diameter, and 1/2 inch for larger piles.
2.
Piles shall be embedded into the footing a minimum of 6 inches. The reinforcing mat shall have 11/2 inches of cover to the top of the pile.
3.
Class 4000 LS Concrete shall be specified for inside the pile. The top 10 feet of concrete in the pile is to be vibrated.
4.
The full cross section of the steel shell, minus 1/16 inch for corrosion, is to be used in determining the pile stiffness and foundation modeling. It can also be considered as confinement reinforcement for the internal cage except at pile/footing interface. The moment of inertia of the pile is to be computed by adding the components I pile = Iconc + (n)(Ishell) + (n)(Ireinf).
5.
A steel reinforcing cage shall be used to tie the pile to the footing. The reinforcement, alone, shall be sufficient to resist the total moment throughout the length of pile without considering the shell. The minimum reinforcement shall be 0.5 percent of the gross concrete area for Seismic Performance Categories A and B, and 0.75 percent for Category C as required per AASHTO’s Seismic Guideline Specifications, Chapter 6. No less than four No. 5 bars shall be used. The reinforcement shall extend above the pile into the footing a distance equal to 1.25 1d (tension).
6.
Above the top of the pile, the vertical steel reinforcing bars shall be tied together with closely spaced hoops or spirals as required by the seismic guide specifications. Inside the pile, No. 4 hoops at 12-inch centers is minimum required for Category B and 9-inch centers for Category C.
B. Concrete Pile Types The following types of concrete piles have been commonly used: 1.
Cast-in-Place Concrete Piles Utilizing Driven Steel Pipe Casings The casing diameter and thickness is called for in the specifications. The bottom of the casing is capped with a suitable flat plate before driving. Special tips are sometimes used when difficult driving is expected.
9.6 - 6
April 1993
BRIDGE DESIGN MANUAL Criteria Substructure Design 2.
Piles and Piling
Precast Concrete Piles These piles may be of various cross-sectional shapes and are reinforced for handling stresses. A good knowledge of the in-place length is required since splicing is difficult. Due to handling requirements, only short lengths can be used. See Standard Plan Sheet E-4 for precast concrete piles, 13-inch diameter.
3.
Precast Prestressed Concrete Piles These piles are hexagonal, square, or circular in cross-section and are prestressed to allow longer handling lengths. Again, close length determination at time of driving the test pile is important. Precast prestresed concrete piles are usually specified in accordance with Standard Plans such as Sheet E-4 for 13-inch diameter piles and Sheet E-4a for 16- and 18-inch diameter piles.
9.6.4
Sheet Piling (H Piles) Steel piles are normally used where there are hard layers which must be penetrated in order to reach an adequate point bearing stratum. Steel stress should be limited to 9.0 ksi (working stress) on the tip. H piling can act efficiently as friction piling due to its large surface area. Do not use steel H piling where the soil consists of only moderately dense material. In such conditions, it may be difficult to develop the friction capacity of the H piles and excessive pile length may result. The bridge layout will denote steel piles with capacity and size, e.g., steel pile 70-ton HP 12 x 53.
9.6.5
Timber Piles Timber piles have the lowest cost per foot of any of the pile types. Timber piles may be untreated or treated. Untreated piles are used only for temporary applications or where the entire pile will be permanently below the water line. Composite piles, treated and untreated, may be used if the pile length is long and a splice will be required. Where composite piles are used, the splice must be located below the permanent water table. If doubt exists as to the location of the permanent water table, treated timber piles shall be used. Where dense material exists, consideration should be given to allowing jetting (with loss of uplift capacity), use of shoes, or use of other pile types.
9.6.6
Sheet Piles Sheet piles are normally used for cofferdam and shoring and cribbing, but are usually not made a part of permanent construction.
9.6.7
Cylinder Piles Large diameter cylinder piles are used because of their high allowable bearing and bending strength capacity. Cylinder piles are commonly cast-in-place concrete and the shaft is formed by drilling. See “Drilled Shafts” Section 9.8.
9-6WORK:V:BDM3
January 1991
9.6 - 7
BRIDGE DESIGN MANUAL Criteria Substructure Design 9.7
Seals
9.7.1
Purpose
Seals
A concrete seal is used within the confines of a cofferdam to permit construction of the pier footing and column in the dry. This type of underwater construction is practical to a water depth of approximately 50 feet. Seal concrete must be placed underwater. This is usually accomplished with the use of a tremie. A tremie is a long pipe that extends to the bottom of the excavation and permits a head to be maintained on the concrete during placement. After the concrete has been placed and has obtained sufficient strength, the water within the cofferdam is removed. The weight of the seal concrete resists the hydrostatic pressure exerting force at the base of the seal. In Figure 9.7.1-1, some of the factors that must be considered in designing a seal are illustrated.
*Usually 1 foot 0 inches for design (use 1 foot 0 inches greater than design seal dimensions for quantity calculations). Figure 9.7.1-1
9.7.2
General A. Normal High Water Elevation The Normal High Water Elevation is defined as the highest water surface elevation that may normally be expected to occur during a given time period. This elevation, which appears on the Hydraulics Data Sheet, is obtained from discussions with local residents or by observance of high water marks at the site. The normal high water is not related to any flood condition.
March 1993
9.7 - 1
BRIDGE DESIGN MANUAL Criteria Substructure Design
Seals
B. Seal Vent Elevation The headquarters Hydraulics Section recommends a seal vent elevation in accordance with the following criteria: 1.
Construction time period not known. If the time period of the footing construction is not known, the vent elevation reflects the normal high water elevation that might occur at any time during the year.
2.
Construction time period known. If the time period of the footing construction can be anticipated, the vent elevation reflects the normal high water elevation that might occur during this time period. (If the anticipated time period of construction is later changed, the Hydraulics Section shall be notified and appropriate changes made in the design.)
C. Scour Depth The depth of the anticipated scour is determined by the Headquarters Hydraulics Section. The bottom of the footing, or bottom of seal, if used, shall be no higher than the scour depth elevation. After preliminary footing and seal thicknesses have been determined, the designers shall review the anticipated scour elevation with the Hydraulics Section to ensure that excessive depths are not used. D. Recommended Foundation Elevation (from Soils Report) Based on the results obtained from test boring made at the site, the Soils Engineer determines a foundation elevation and accompanying soil pressure that will not result in excessive settlement of the structure. If other factors control, such as scour or footing cover, the footing elevation may have to be lower than determined by the Soils Engineer.
9.7.3
Spread Footings A. Seal Positively Required When there is little possibility of the seal being eliminated during construction, the following procedure shall be used for design: 1.
Preliminary Sections The bottom of the seal elevation shall be the lower of the scour elevation or the foundation elevation as recommended by the Soils Engineer. Footing cover requirements of Section 9.5 apply when the top of footing is exposed to view. The size of the seal is selected based on the following: a.
Allowable Soil Pressure The size of the seal required in order to meet the allowable soil pressure shall be calculated using column moments at the base of the footing and vertical load applied at the bottom of the seal.
b.
Stability Stability need only be checked at the base of the footing.
2.
Final Design After preliminary sections are determined, the final design is made based on the criteria outlined in Section 9.5.
9.7 - 2
March 1993
BRIDGE DESIGN MANUAL Criteria Substructure Design 3.
Seals
Unusual Conditions At times, unusual conditions are encountered such as rock formations or deep foundations that require special considerations in order to arrive at the most optimum design. When this occurs, it is advisable to discuss the proposed foundation design with both the Soils Engineer and the Bridge Hydraulics Section prior to final plan preparation.
B. Seal May Not Be Required When it is possible but not probable that a seal may be required during construction, the seal and footing are designed as described in Section 9.7.3A. In addition, a separate design is made for a footing without a seal. The top of the footing, or pedestal when used, shall be no higher than the elevation set by cover requirements. The bottom of the footing shall be no higher than the foundation elevation recommended by the Soils Engineer or the scour elevation set by Headquarters Hydraulics. This alternate footing without a seal shall be detailed on the plans. If the alternate footing elevation is different from the footing with seal, it is also necessary to note on the plans the required changes in length of column bars and increased number of ties. The quantities shall be based on the footing designed with a seal. Both designs shall be included in the plans.
9.7.4
Pile Support Footings The top of the footing, or pedestal when used, is set by cover requirements of Section 9.5. The bottom of seal elevation is based on the stream scour elevation determined by Hydraulics. A preliminary analysis is made using the estimated footing and seal weight, and the column moments and vertical load at the base of the footing to determine the number of piles and spacing. Seal size will be 1 foot 0 inches larger than the footing all around. From Design Aid 9.7-A1, the seal thickness can be obtained based on the vent elevation. After preliminary dimensions are determined, the final design is made using the criteria outlined in Section 9.5. If the seal is omitted during construction, the bottom of footing shall be set at the scour elevation and an alternate design is made.
9-7:V:BDM9
March 1993
9.7 - 3
BRIDGE DESIGN MANUAL Criteria Substructure Design 9.8
Drilled Shafts
9.8.1
General
Drilled Shafts
A. Definition A drilled shaft is a machine and/or manually excavated shaft in soil or rock that is filled with concrete and reinforcing steel. A drilled shaft is circular in cross-section and may be belled at the base to provide greater bearing area. Vertical load is resisted by the drilled shaft in base bearing and side friction. Horizontal load is resisted by the shaft in horizontal bearing against the surrounding soil or rock. B. Characteristics The following special features distinguish drilled shaft from other types of foundations: 1.
The drilled shaft is installed in a drilled hole, unlike the driven pile.
2.
Wet concrete is cast and cures directly against the soil forming the walls of the bore hole. Temporary steel casing may be necessary for stabilization of the open hole and is extracted during concrete placement.
3.
The installation method for drilled shafts is adapted to suit the subsurface conditions.
C. Terminology Other terminology commonly used to describe a drilled shaft includes: drilled pier, drilled caisson, and bored pile. In soil, the shaft is normally drilled with an auger. In rock, a core barrel bit is used in combination with blasting.
9.8.2
Types of Drilled Shafts Drilled shafts may be categorized by two different methods. The first method defines shafts by their load transfer. The second method classifies shafts by their type of construction. A. Classification by Load Transfer to the Soil 1.
Straight shaft, end-bearing drilled shaft. Load is transferred by base resistance only.
2.
Straight shaft, side-wall shear or friction drilled shaft. Load is transferred by shaft shear resistance only.
3.
Straight shaft, side-wall shear and end-bearing drilled shaft. Load is transferred by combination of shaft and base resistance.
4.
Belled or underreamed drilled shaft. Load is transferred by the bell in end-bearing. Shaft shear resistance may be considered, depending on the dimensions of the drilled shaft and overburden material.
5.
Straight or belled drilled shaft on hard soil or rock. Shaft shear resistance may be considered, under some circumstances, when the shaft is socketed into good rock.
B. Classification by Type of Construction
January 1991
1.
Not cased, reinforced.
2.
Temporary casing, removed while placing concrete.
3.
Temporary casing with permanent liner.
9.8 - 1
BRIDGE DESIGN MANUAL Criteria Substructure Design
9.8.3
4.
Permanent casing.
5.
Underreamed shafts.
6.
Underwater concrete placement.
Drilled Shafts
Advantages and Disadvantages of the Drilled Shaft A. Advantages 1.
Construction equipment is normally mobile and construction can proceed rapidly.
2.
The excavated material and the drilled hole can often be examined to ascertain whether or not the soil conditions at the particular site agree with the projected soil profile.
3.
Changes in geometry of the drilled shaft may be made during the progress of a job if the subsurface conditions so dictate. These changes include adjustment in diameter and in penetration and the addition or exclusion of underreams.
4.
The heave and settlement at the ground surface will normally be very small.
5.
The personnel, equipment, and materials for construction are usually readily available.
6.
The completed excavation can often be carefully inspected prior to construction if casing or slurry is not required. For end-bearing situations, the soil beneath the tip of the drilled shaft can be probed for cavities or for weak soil.
7.
The noise level from the equipment is less than for some other methods of construction.
8.
The drilled shaft is applicable to a wide variety of soil conditions For example, it is possible to drill through a layer of cobbles, many feet into sound rock, and through frozen ground.
9.
Very large loads can be carried by a single drilled shaft.
10. Designs of drilled shafts can be made considering load transfer both in end bearing and in side resistance. 11. The behavior of a drilled shaft at a site can be monitored by available methods of instrumentation and analytical techniques. 12. Use in constricted areas. The shaft occupies less area than a footing and thus can be built closer to railroads and existing structures. 13. When drilling inside a steel casing, pollution of lake or river water is minimized. 14. Drilled shafts may be more economical than spread footing construction, especially when the foundation is deep. B. Disadvantages
9.8 - 2
1.
Construction procedures are critical to the quality of the drilled shaft, and very careful inspection is required.
2.
Construction techniques are sometimes very sensitive to subsurface soil and rock conditions. Boulders can be a serious problem, especially in smaller diameter shafts.
3.
The proper performance and interpretation of load tests on drilled shafts requires expert knowledge and experience.
4.
Lack of general knowledge of construction problems and design methods has restricted the use of drilled shafts.
BRIDGE DESIGN MANUAL Criteria Substructure Design
9.8.4
5.
Shaft length within predicted scour range is not considered effective.
6.
Reduced redundancy, with fewer number of shafts versus a large number of piles.
Drilled Shafts
Preliminary Soils Investigation For proper design and construction, a site investigation is very important not only to the design engineer, but to the contractor as well. All information that is gained in a site investigation should be made available to potential contractors. A. Surface Features A careful review of Surface Features should be made from the field data and soils report. Surface features, such as boulders or cobbles, may dictate whether drilled shafts are feasible or desirable. Among the things to be aware of are the following: 1.
The existence of utilities and any restrictions concerning their relocation or removal.
2.
A drilled shaft requires less area than a footing and is appropriate as foundation support near existing structures or facilities such as railroad tracks. With less area, excavation, shoring, and cribbing costs are reduced. Installation of drilled shafts produce less noise and vibration than pile driving.
3.
Water table elevation will influence the method of construction of the drilled shaft. A casing may be used to place concrete in the dry or a tremie used to place concrete in water or slurry.
4.
A contour map may be needed to determine the finished top elevation of the drilled shaft.
5.
Site access by construction equipment.
6.
Environmental considerations may also dictate the methods of construction.
B. Subsurface Investigation A preliminary soils investigation and testing is needed to determine the pertinent characteristics of the soil in which the drilled shaft is to be constructed. The characteristics of the soil will influence the design of the shaft and the method of construction. C. Methods of Investigation The standard method for obtaining soil characteristics involves laboratory testing of undisturbed samples and the use of in-situ techniques such as: Goodman Jack, the static cone test, and pressuremeter tests. The standard penetration test is used extensively. D. Subsurface Conditions Affecting Construction
January 1991
1.
The stability of the subsurface soils when the excavation is made will determine whether a casing is necessary or not. The dry method (see Section 9.8.7A) of construction can be used only where the soils will not cave or collapse. The casing or slurry method (see Section 9.8.7B and 9.8.7C) must be used if there is danger of caving or collapse.
2.
It must be determined if groundwater exists at the site and what rate of flow can be expected into a shaft excavation. The presence of groundwater will indicate if a tremie pour shaft will be needed or if a tremie seal must first be poured, the shaft dewatered, and then the remainder of the shaft poured in the dry. In either instance, the design must assure access to the top of the seal to allow the surface to be thoroughly cleaned prior to placing additional concrete (i.e., the shaft must be large enough to accommodate a worker or the top surface of a small diameter shaft seal must be located so that it is accessible).
9.8 - 3
BRIDGE DESIGN MANUAL Criteria Substructure Design
9.8.5
Drilled Shafts
3.
Any artesian water conditions must be clearly identified in the contract documents. Artesian water flowing into a pour could spoil the concrete or cause collapse or heaving of the soil at the excavation.
4.
The presence of cobbles or boulders can cause difficulties in drilling. Drilling with core barrel bits or blasting can remove obstructions.
5.
The presence of existing foundations or structures.
6.
Presence of landfill that could contain hazardous or dangerous material that cannot be easily excavated.
7.
Presence of rock may require more sophisticated drilling methods or shooting with explosives.
8.
Presence of a weak stratum below the base of the drilled shaft. For this situation, drilling may have to be extended below the weak stratum.
Design of Drilled Shafts for Axial Load The total axial capacity of the drilled shaft is composed of two factors: the base capacity and the side capacity. The general formula is: QT = QB + QS QT = total axial capacity of the foundation QB = the base capacity QS = the side capacity QB and QS are treated as independent quantities although research has shown that the base resistance and side resistance have some independence. The degree of reliability of the above formula is compatible with the soils information obtained from a routine investigation. Ultimate unit base resistance and side resistance will be obtained from the Foundation Engineer. Unit side resistance may vary with depth, but normally one value is given for the entire depth of the shaft. Ultimate base and side resistances are furnished by the Foundation Engineer along with a factor of safety. A. Ultimate Failure vs. Excessive Settlement There are basically two criteria by which recommendations for unit base and shaft resistances are arrived at by the Foundation Engineer. First, the ultimate soil resistance is determined using limit state criteria. Second, an estimate of the settlement of the shaft is made using anticipated loads. If it is felt that settlements are excessive, then the settlement criteria will control the design of the shaft. The designer should indicate to the Foundation Engineer what settlements would be acceptable in the design. Normally 1 inch is adequate. It must be cautioned, however, that in deep shafts, it is sometimes necessary to have vertical deflections on the order of 2 percent of the shaft diameter in order to develop the base resistance. B. Factor of Safety For the design of drilled shafts, the Foundation Engineer should be consulted on ultimate base and shear resistances along with a factor of safety. Drilled shafts are designed by load factor methods. For factored load combinations, see Section 9.5.1(3b) for Maximum Pile Load. Group I Basic Service Loads are checked against allowable axial bearing and side friction supplied from the Materials Lab.
9.8 - 4
BRIDGE DESIGN MANUAL Criteria Substructure Design
Drilled Shafts
C. Spacing, Depth, Diameter Reinforcing, and Concrete Strength of Drilled Shafts 1.
Spacing In situations where the design load cannot be sustained by a single shaft, several drilled shafts may be installed to act as a group. If the spacing between shafts in a group is too small, excessive settlement may occur along with a reduction in the side resistance. As a guide to design, an efficiency of 70 percent is recommended for drilled shaft groups in clay and 100 percent for groups in sand, when the spacing between shafts is in the range of 2.5B to 4B (B = shaft diameter). The Foundation Engineer will normally give a recommendation on spacing between shafts in a group.
2.
Depth In order to develop a high base resistance, the drilled shaft must have sufficient depth of soil above the base. Depths between 3B and 5B (B = shaft diameter) are recommended for design. The Foundation Engineer will normally recommend a depth. There may be a limitation on the depth of penetration due to equipment limitations. Penetrations of 100 feet and more are not uncommon.
3.
Diameter The diameter of a shaft should be a minimum of 18 inches. The shaft diameters should be specified in 6-inch increments. The maximum diameter of the shaft depends on the availability of equipment. Diameters in the order of 10 feet to 12 feet are common.
4.
Reinforcing and Concrete Strength Due to soil conditions and construction methods, concrete may not be placed in the dry. A reduction in concrete strength used for design shall be as follows: a.
Shaft diameter 4 feet 0 inches or less – assumed concrete compressive strength shall be 0.85 fc′. Concrete placed by tremie method is confined to small area and segregation is reduced. Cover requirement – 3-inch minimum to 6-inch maximum.
b.
Shaft diameter 4 feet 6 inches or more – use 0.60 fc′. Cover requirement – 6-inch minimum to 12-inch maximum.
Reinforcing shall be detailed to minimize congestion. Longitudinal reinforcing extending into footing should be straight. If hooked, detail so that casing can be removed while placing concrete. Percentage of reinforcing shall be 0.5 percent minimum and 4 percent maximum. Use of two concentric circular cages shall be avoided.
January 1991
9.8 - 5
BRIDGE DESIGN MANUAL Criteria Substructure Design 9.8.6
Drilled Shafts
Design of Drilled Shafts Subject to Lateral Loads A. General Modeling Technique The modeling technique involved in the analysis of laterally loaded shafts depicts the soil surrounding the shaft as a set of linear or nonlinear elastic springs. See Figure 9.8.6-1 for illustration.
Model of Laterally Loaded Shaft Figure 9.8.6-1 Present day computer analysis techniques can handle a finite number of springs. The correct mathematical solution involves the solution of an infinite number of springs. The problem is one of a beam-on-elastic foundation which involves the solution of a fourth order differential equation. The exact mathematical solution is normally difficult except in the very limited cases. Therefore, this method of solution is considered impractical for the normal design problems. The most practical means for analysis of the drilled shaft for lateral loads is by computer. For additional modeling techniques, see Chapter 4 Foundation Modeling.
9.8 - 6
BRIDGE DESIGN MANUAL Criteria Substructure Design
Drilled Shafts
B. P-Y Curves Horizontal deflection of the soil due to load is normally represented by “P-Y” curves. P stands for a force per unit length of the shaft such as kips per foot. Y is the horizontal deflection of the shaft in units such as feet. The P-Y relationship usually will vary with depth of the shaft. A reduction for group action will be required if the shafts are spaced less than three diameters normal to the direction of loading and less than six to eight diameters parallel to the direction of loading. The Foundation Engineer will provide the design engineer with P-Y curves for the design of the drilled shafts. A set of P-Y curves must be derived for computer analysis of a drilled shaft.
Set of Nonlinear P-Y Curves Figure 9.8.6-2
January 1991
9.8 - 7
BRIDGE DESIGN MANUAL Criteria Substructure Design
Drilled Shafts
Another concept in soil mechanics is that of the Soil Modulus “ES” which is defined as -P/Y. This term will have units such as kips per square foot.
Illustration of the Secant Modulus Figure 9.8.6-3 The soil modulus is taken as being a linear function of depth. Since the P-Y relationship is nonlinear, the modulus ES will be a secant modulus. C. Analysis by Computer 1.
Dr. Reese Program The “Analysis of Laterally Loaded Piles” program by Dr. Lymon Reese will accommodate P-Y curve input data for the solution of laterally loaded piles. Linear P-Y curves are generated for different soil layers with known soil properties. The program referred to as “LPILE1” will not allow simultaneous solution of the superstructure and substructure. The program is most commonly used to analyze shafts.
2.
PILANA This acronym describes a modeling technique, using STRUDL, to solve lateral loads on piles. The soil spring coefficient (P-Y relationship) must be linear. Superstructure and substructure may be solved for simultaneously.
3.
Pile — Structure Interaction Analysis The McAUTO STRUDL program will solve the lateral load on a pile problem. P-Y curve relationship values may be entered directly. P-Y values may be linear or nonlinear. Both superstructure and substructure may be analyzed simultaneously. The McAUTO STRUDL program has the most capabilities of the three computer programs listed.
9.8 - 8
BRIDGE DESIGN MANUAL Criteria Substructure Design
Drilled Shafts
D. Shaft Design 1.
Stability Normally, the soil surrounding a foundation element provides bracing against a buckling failure. For this reason, the drilled shaft can be designed as a short column when the shaft is entirely below the groundline. When the shaft extends above the ground a check for stability should be made. See Section 9.2.1E of the Bridge Design Manual Criteria. The effects of scour must be considered in the analysis.
2.
Axial Load, Bending Moment, and Shear The axial load along the shaft varies due to the side friction. It is considered conservative, however, to design the shaft for the full axial load plus the maximum moment. The entire shaft normally is then reinforced for this axial load and moment, Longitudinal reinforcing should not be less than 0.5 percent of the area of concrete. Design shaft for axial load bending movement and shear similar to the design of a column.
9.8.7
Construction Methods A. Dry Method The dry method is applicable to soils above the water table that will not cave or slump when the hole is drilled to its full depth. A soil that meets this specification is a homogenous stiff clay. The dry method can be employed with sands above the water table if the sands have some cohesion. The dry method can be used for soils below the water table if the soils are low in permeability so that only a small amount of water will seep into the hole during the time the excavation is open. The dry method consists of drilling a hole, without casing, placing a rebar cage, and then filling the hole with concrete. B. Casing Method The casing method is applicable to sites where soil conditions are such that caving or excessive deformation will occur when a hole is excavated. An example of such a site is a clean sand below the water table. This method employs a cylindrical (usually steel) casing inside the hole to hold back the caving soil. The casing is removed from the hole during concrete placement. C. Slurry Displacement Method A Bentonite Slurry is introduced into the excavated hole to prevent caving or deformation of loose or permeable soils. Drilling continues through the slurry. When the desired depth is reached, the rebar cage is lowered into the hole and the slurry. Concrete is then tremie poured into the hole. Slurry is displaced by the heavier concrete and collected at the surface in a sump. The slurry may be used again in another hole.
9-8WORK:V:BDM9
January 1991
9.8 - 9
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
9.9
Application of LRFD Code to WSDOT Foundation Design
9.9.1
Overall Design Process, Roles, and Responsibilities A flowchart is provided in Figure 9.9.1-1 which illustrates the overall design process needed to accomplish an LRFD foundation design. The steps in the flowchart are defined as follows: Conceptual Bridge Foundation Design — This design step results in an informal communication produced by the Geotechnical Branch at the request of the Bridge and Structures Office which provides a brief description of the anticipated site conditions, an estimate of the maximum slope feasible for the bridge approach fills for the purpose of determining bridge length, conceptual foundation types feasible, and conceptual evaluation of potential geotechnical hazards such as liquefaction. In general, no test holes are drilled at this stage, as only existing site data is used for this determination. The purpose of these recommendations is to provide enough geotechnical information to allow the bridge preliminary plan to be produced. Develop Site data and Preliminary Bridge Plan — During this phase, the Bridge and Structures Office obtains site data from the region (see WSDOT Design Manual) and develops a preliminary bridge plan adequate for the Geotechnical Branch to locate borings in preparation for the final design of the structure (i.e., pier locations are known with a relatively high degree of certainty). The Bridge and Structures Office would also provide the following information to the Geotechnical Branch to allow them to adequately develop the preliminary foundation design: • Anticipated structure type and magnitudes of settlement (both total and differential) the structure can tolerate. • At abutments, the approximate maximum elevation feasible for the top of the foundation in consideration of the foundation depth. • For interior piers, the number of columns anticipated, and if there will be single foundation elements for each column, or if one foundation element will support multiple columns. • At stream crossings, the depth of scour anticipated, if known. Typically, the Geotechnical Branch will pursue this issue with the OSC Hydraulics Office. • Any known constraints that would affect the foundations in terms of type, location, or size, or any known constraints which would affect the assumptions which need to be made to determine the nominal resistance of the foundation (e.g., utilities that must remain, construction staging needs, excavation, shoring and falsework needs, other constructability issues). Preliminary Foundation Design — This design step results in a memorandum produced by the Geotechnical Branch at the request of the Bridge and Structures Office which provides geotechnical data adequate to do the structural analysis and modeling for all load groups to be considered for the structure. The geotechnical data is preliminary in that it is not in final form for publication and transmittal to potential bidders. In addition, the foundation recommendations are subject to change, depending on the results of the structural analysis and modeling and the effect that modeling and analysis has on foundation types, locations, sizes, and depths, as well as any design assumptions made by the geotechnical designer. Preliminary foundation recommendations may also be subject to change depending on the construction staging needs and other constructability issues which are discovered during this design phase. Geotechnical work conducted during this stage typically includes completion of the field exploration program to the final PS&E level, development of foundation types and capacities feasible, foundation
July 2000
9.9-1
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
depths needed, P-Y curve data and soil spring data for seismic modeling, seismic site characterization and estimated ground acceleration, and recommendations to address known constructability issues. A description of subsurface conditions and a preliminary subsurface profile would also be provided at this stage, but detailed boring logs and laboratory test data would usually not be provided. Structural Analysis and Modeling — In this phase, the Bridge and Structures Office uses the preliminary foundation design recommendations provided by the Geotechnical Branch to perform the structural modeling of the foundation system and superstructure. Through this modeling, the Bridge and Structures Office determines and distributes the loads within the structure for all appropriate load cases, factors the loads as appropriate, and sizes the foundations using the foundation nominal resistances and resistance factors provided by the Geotechnical Branch. Constructability and construction staging needs would continue to be investigated during this phase. The Bridge and Structures Office would also provide the following feedback to the Geotechnical Branch to allow them to check their preliminary foundation design and produce the Final Geotechnical Report for the structure: • Anticipated foundation loads (including load factors and load groups used). • Foundation size/diameter and depth required to meet structural needs. • Foundation details which could affect the geotechnical design of the foundations. • Size and configuration of deep foundation groups. Final Foundation Design — This design step results in a formal geotechnical report produced by the Geotechnical Branch which provides final geotechnical recommendations for the subject structure. This report includes all geotechnical data obtained at the site, including final boring logs, subsurface profiles, and laboratory test data, all final foundation recommendations, and final constructability recommendations for the structure. At this time, the Geotechnical Branch will check their preliminary foundation design in consideration of the structural foundation design results determined by the Bridge and Structures Office, and make modifications to the preliminary foundation design as needed to accommodate the structural design needs provided by the Bridge and Structures Office. It is possible that much of what was included in the preliminary foundation design memorandum may be copied into the final geotechnical report, if no design changes are needed. This report will also be used for publication and distribution to potential bidders. Final Structural Modeling and PS&E Development — In this phase, the Bridge and Structures Office makes any adjustments needed to their structural model to accommodate any changes made to the geotechnical foundation recommendations as transmitted in the final geotechnical report. From this, the bridge design and final PS&E would be completed.
9.9-2
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Bridge and Structures Office (BO) requests conceptual foundation recommendations from Geotechnical Branch (GB)
▼ GB provides conceptual foundation recommendations to BO
▼ GB provides preliminary foundation design recommendations
▼
BO obtains site data from region, develops draft preliminary bridge plan, and provides initial foundation needs input to GB
▼ ▼
▼
BO performs structural analysis and modeling, and provides feedback to GB regarding foundation loads, type, size, depth, and configuration needed for structural purposes
GB performs final geotechnical design as needed and provides final geotechnical report for the structure
▼ BO performs final structural modeling (if necessary) and develops final PS&E for structure
Overall Design Process for LRFD Foundation Design Figure 9.9.1-1
July 2000
9.9-3
BRIDGE DESIGN MANUAL Criteria Substructure Design 9.9.2
Application of LRFD Code to WSDOT Foundation Design
Definitions and Geometry Use Figure 9.9.2-1 below to provide a common basis of understanding for loading locations and directions for substructure design. This figure also describes the geometric data required for abutment and substructure design. Note that for shaft and some pile foundation designs, the shaft or pile may form the column as well as the foundation element, thereby eliminating the footing element shown in the figure.
Template for Foundation Site Data and Loading Direction Definitions Figure 9.9.2-1 Note that in the guidelines which follow, where reference is made to an article or table in the AASHTO specifications, the article can be found in the 1998 AASHTO LRFD specifications, Second Edition, with Interims.
9.9-4
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design 9.9.3
Application of LRFD Code to WSDOT Foundation Design
Load Factors The load combinations and factors to be used for foundation design are provided in Table 9.9.3-1 and Table 9.9.3-2. These have been adapted from Table 3.4.1-2 of the 1998 AASHTO LRFD specifications, Second Edition and have been reproduced from the AASHTO LRFD Bridge Design Specifications. Note that these tables are reproduced from the AASHTO specifications in their entirety for convenience only. Consult the most recent publication of the AASHTO LRFD Bridge Design Specifications to determine the current load factors for design, with the exception of load factors which are identified herein as specific to WSDOT practice.
Load Combinations and Load Factors (from AASHTO LRFD Specifications Table 3.4.1-1) Table 9.2.3-1 Load Combination
DC DD DW EH EV ES
LL IM CE BR PL LS
WA
Strength-I
γp
1.75
1.00
–
–
1.00
0.50/1.20
γ
Strength-II
γp
1.35
1.00
–
–
1.00
0.50/1.20
γ
Strength-III
γp
–
1.00
1.40
–
1.00
0.50/1.20
γ
Strength-IV EH, EV, ES, DW DC only
γp 1.5
–
1.00
–
–
1.00
0.50/1.20
Strength-V
γp
1.35
1.00
0.40
0.40
1.00
0.50/1.20
Extreme Event-I
γp
γ
1.00
–
–
1.00
–
–
Extreme Event-II
γp
0.50
1.00
–
–
1.00
–
–
Service-I
1.00
1.00
1.00
0.30
0.30
1.00
0.50/1.20
Service-II
1.00
1.30
1.00
–
–
1.00
0.50/1.20
Service-III
1.00
0.80
1.00
–
–
1.00
0.50/1.20
–
0.75
–
–
–
–
–
Limit State
Fatigue-LL, IM and CE only
July 2000
EQ
WS
WL
FR
TU CR SH EL
TG
TG TG TG
SE
γ γ γ
–
γ
γ
TG
TG
γ
– γ
TG
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1.00
–
–
–
–
–
1.00
1.00
1.00
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
SE SE
SE
SE
– γ
CV
–
SE
–
γ
Use One of These at a Time EQ IC CT
SE
–
9.9-5
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Load Factors for Permanent Loads, γp (Adapted from Table 3.4.1-2 of the AASHTO LRFD Specifications, but modified as shown below) Table 9.9.3-2 Load Factor Type of Load
Maximum
Minimum
DC: Components and Attachments
1.25
0.9
DD: Downdrag
1.00*
1.00*
DW: Wearing Surfaces and Utilities
1.50
0.65
EH: Horizontal Earth Pressure • Active • At-Rest
1.50 1.35
0.90 0.90
1.35 1.30 1.35
1.00 0.90 0.90
1.95 1.50
0.90 0.90
.50
0.75
EV: Vertical Earth Pressure • Retaining Structure • Rigid Buried Structure • Rigid Frames • Flexible Buried Structures other than Metal Box Culverts • Flexible Metal Box Culverts ES: Earth Surcharge
*DD was reduced to 1.00 to reflect current WSDOT and national practice. Permanent Load Factors DC = dead load of structural components and non structural attachments DD = downdrag DW = dead load of wearing services and utilities EH = horizontal earth pressure load EV = vertical pressure from dead load of earth fill ES = earth surcharge load EL = accumulated locked-in force effects resulting from the construction process Various Transient Load Factors BR = vehicular braking force LS = live load surcharge CE = vehicular centrifugal force PL = pedestrian live load CR = creep SE = settlement CT = vehicular collision force SH = shrinkage CV = vessel collision force TG = temperature gradient EQ = earthquake TU = uniform temperature FR = friction WA = water load and stream pressure IC = ice load WL = wind on live load IM = vehicular dynamic load allowance WS = wind load on structure LL = vehicular live load The load factors γTG and γSE are to be determined on a project specific basis in accordance with Articles 3.4.1 and 3.12 of the AASHTO LRFD Specifications.
9.9-6
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design 9.9.4
Application of LRFD Code to WSDOT Foundation Design
LRFD Load Combinations, Basic Equation, and Characteristic Soil/Rock Properties The controlling load combinations for WSDOT projects for Super and Substructure Design are as follows: Strength I Strength III Strength IV Strength V Extreme-Event I Service I
Relating to the normal vehicular use Relating to the bridge exposed to wind Relating to temperature fluctuations, creep, and shrinkage Relating to the normal vehicular use and wind Relating to earthquake Relating to normal operational use and wind
In general, for Extreme Event I, set γEQ, the earthquake load factor, equal to 0 (note that γEQ up to 0.5 should be considered on a project specific basis to account for potential partial live loads during a seismic event). For eccentrically loaded footings and abutment wall footings, use γEQ = 0.0 or 1.0, depending on the maximum resultant force eccentricity allowed (see “Overturning Stability for Footings — Strength and Extreme Event Limit States”). A. LRFD Basic Equation The basic equation for load and resistance factor design (LRFD) states that the loads multiplied by factors to account for uncertainty, ductility, importance, and redundancy must be less than or equal to the available resistance multiplied by factors to account for variability and uncertainty per the AASHTO LRFD specifications. The basic equation, therefore, is as follows: Σηiγi Qi ≤ φRn ηi γi Qi φ Rn
= = = = =
Factor for ductility, redundancy, and importance of structure Load factor Load (i.e., dead load, live load, seismic load, etc.) Resistance factor Nominal or ultimate resistance
For typical WSDOT practice, ηi should be set equal to 1.0 for use of both minimum and maximum load factors. B. Characteristic Soil/Rock Properties and Their Use in LRFD Load and resistance factors are based on a combination of the following: • design model uncertainty, • soil/rock property uncertainty, • unknown uncertainty inherited from allowable stress and load factor design practices included in previous AASHTO design specifications. Therefore, uncertainty in the soil parameters only amounts for a part of each of the load and resistance factors.
July 2000
9.9-7
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Assume that the characteristic soil/rock properties used in conjunction with the load and resistance factors provided herein are average values obtained from laboratory test results or from correlated field in-situ test results. Note that use of lower bound soil/rock properties could result in overly conservative foundation designs. No specific guidance is available regarding the extent of subsurface characterization and the number of soil/rock property tests required to justify use of the load and resistance factors provided herein. Geotechnical engineering judgment is required. No adequate documentation exists regarding the derivation of load factors for soil loads to have any basis for adjusting the load factors for site specific considerations, or for regional practice. However, there is some documentation available regarding the derivation of resistance factors for foundations. This makes it possible to adjust the resistance factors for site specific considerations and regional practices. See the Federal Highway Administration manual FHWA HI-98-032 “Load and Resistance Factor Design (LRFD) for Highway Bridge Substructures,” 1998, for the necessary statistical information and procedures for making such an adjustment. Appendix A of this section has an example of resistance factor adjustment as applied to a pile foundation design. Adjustments to soil resistance factors, where warranted, will be made by the Geotechnical Branch if adequate data is available to do so.
9.9-8
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design 9.9.5
Application of LRFD Code to WSDOT Foundation Design
Spread Footing Design Figure 9.9.5-1 provides a flowchart which illustrates the design process and the interaction between the structural geotechnical engineers needed for footing design. 1(ST). Determine bridge geometry and pier locations
▼
1(GT). Determine depth of footing based on geometry and bearing material
▼
▼ 1(GT). Determine depth of footing for scour, if present (with help of Hydraulic Engineer)
2(ST). Determine loads applied to footing, including lateral earth pressure loads for abutments ▼ 3(ST). Design the footing at the service limit state ▼
▼ 3(GT). Determine soil properties for foundation design, and resistance factors in consideration of the soil property uncertainty and the method selected for calculating nominal resistance
4(ST). Check the bearing pressure of the footing at the strength limit state ▼ 5(ST). Check the eccentricity of the footing at the strength limit state
▼ 4(GT). Determine active, passive, and seismic earth pressure parameters as needed for abutments
▼ 6(ST). Determine nominal footing resistance at the service limit state
8(GT). Check nominal footing resistance at all limit states, and overall stability in light of new footing dimensions, depth, and loads
▼ 7(ST). Check the bearing pressure of the footing at the extreme limit state ▼ 8(ST). Check the eccentricity of the footing at the extreme limit state
▼
▼ 7(GT). Check overall stability, determining max. feasible bearing load to maintain adequate stability
▼
▼ 5(GT). Determine nominal footing resistance at the strength and extreme limit states
▼ 6(ST). Check the sliding resistance of the footing at the strength limit state
▼ 9(ST). Check sliding resistance of the footing at the extreme limit state ▼ 10(ST). Design the footing (and walls for abutment) according to the concrete section of the Specification
GT: ST:
Geotechnical Engineer Bridge Engineer
Design Flowchart for Spread Footing Design Figure 9.9.5-1
July 2000
9.9-9
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
A. Loads and Load Factor Application to Spread Footings Figures 9.9.5-2 and 9.9.5-3 provides definitions and locations of the forces and moments which act on structural footings. Table 9.9.5-1 identifies when to use maximum or minimum load factors for the various modes of failure for the footing (sliding, overturning, bearing capacity) for each force. Note that the eccentricity used to calculate the bearing stress is referenced to point C, whereas the eccentricity used to evaluate overturning is referenced to point O. It is important to not change from maximum to minimum load factors in consideration of the force location relative to the reference point used (“C” or “O”), as doing so will cause basic statics to no longer apply, and one will not get the same resultant location when the moments are summed at different reference points. Also note that the loads are factored after they are distributed to the foundation through structural analysis and modeling.
Definition and Location of Forces and Moments for Cantilever (or Overhanging) Abutments Figure 9.9.5-2
9.9-10
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Definition and Location of Forces and Moments for L-abutments and Interior Footings Figure 9.9.5-3
July 2000
9.9-11
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
The variables shown above in Figures 9.9.4-1 and 9.9.4-2 are defined as follows: DLv, LLv, EQv
Ws Wtoe
= vertical structural loads applied to footing/wall (dead load, transient load, EQ load, respectively) = structural static shear loads transmitted through bearing at wall top (parallel to abutment wall or transverse to bridge, respectively) = structural static shear loads transmitted through bearing at wall top (normal to abutment wall or longitudinal to bridge, respectively) = structural seismic shear loads transmitted through bearing at wall top (parallel to abutment wall or transverse to bridge, respectively) = structural seismic shear loads transmitted through bearing at wall top (normal to abutment wall or longitudinal to bridge, respectively) = weight of soil above abutment wall heel = weight of soil above footing toe
WC
= weight of footing and column/wall
Ft
= soil active force behind abutment wall (use at rest earth pressure if have an integral abutment) = traffic surcharge force behind abutment wall = dynamic horizontal thrust due to seismic loading = soil and wall mass inertial force due to seismic loading = ultimate soil passive resistance (note: height of pressure distribution triangle is determined by the geotechnical engineer and is project specific)
τp or τt τn or τl τEQp or τEQt τEQn or τEQl
Fq PAE PIR QEP Qτ
= soil shear resistance along footing base at soil-concrete interface
sv R eC
= resultant vertical bearing stress at base of footing = resultant force at base of footing = eccentricity calculated about point C (center of footing), to be used for bearing stress calculations = eccentricity calculated about point O (toe of footing), to be used for overturning calculations = footing width = footing length = traffic live load surcharge pressure
eO B L q
9.9-12
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Selection of Maximum or Minimum Spread Footing Foundation Load Factors for Various Modes of Failure for the Strength and Extreme Event Limit States Table 9.9.5-1 Load Factor Load
Sliding
Overturning, eo
Bearing Stress (ec, sv)
DLv
DCmin, DWmin
DCmin, DWmin
DCmax, DWmax
LLv
Use transient load factor (e.g., LL)
Use transient load factor (e.g., LL)
Use transient load factor (e.g., LL)
τp , τt, τn τ1
Use DCmax, DWmax for causing forces, DCmin, DWmin for resisting forces
Use DCmax, DWmax for causing forces, DCmin, DWmin for resisting forces
Use DCmax, DWmax for causing forces, DCmin, DWmin for resisting forces
Ws, Wtoe
EVmin
EVmin
EVmax
Wc
DCmin
DCmin
DCmax
Ft
EHmax
EHmax
EHmax
Fq
LS
LS
LS
q
Set = 0
Set = 0
Use transient load factor (e.g., LL)
Note that the dead load, DLv, as used herein typically includes the load due to structural components and non-structural attachments (i.e., DC), and the dead load of wearing surfaces and utilities (i.e., DW). The live load, LLv, as used herein for foundation design can include any of the transient loads identified previously except vehicular dynamic load allowance, IM, and loads due to earthquake, EQ. B. Footing Bearing Stress and Capacity — Strength and Extreme Event Limit States For geotechnical and structural design of eccentrically loaded footings on soil, calculate the bearing stress based on a uniform bearing pressure distribution using the Meyerhof approach. For geotechnical and structural design of eccentrically loaded spread footings on rock, calculate the bearing stress based on a triangular or trapezoidal bearing pressure distribution. The Meyerhof method is summarized as follows: Step 1: Calculate eccentricity, ec, about Point C in Figure 9.9.5-2 or Figure 9.9.5-3, with the applied loads already factored. ec
July 2000
=
(summation of factored moments acting on footing and wall)/(summation of factored vertical forces acting on footing and wall)
9.9-13
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Step 2: Calculate the factored vertical stress based on a uniform pressure distribution acting on the base of footing, σv as illustrated in Figure 9.9.5-2 or Figure 9.9.5-3. Note that this calculation method applies in both directions for biaxially loaded footings (see Article 10.6.3.1.5 in the AASHTO LRFD specifications for guidance on biaxial loading). σv =
(summation of factored vertical forces acting on footing and wall per unit footing length)/(B-2ec)
Use the appropriate maximum or minimum load factors as shown in Table 9.9.5-2 when calculating sv. Note that B - 2ec is considered to be the effective footing width B′. If a triangular distribution is used for the footing contact pressure (applies to footings on rock only): σvmax
=
V/B ( 1+ 6 ec / B )
“V” is the sum of the factored vertical forces on the footing. Step 3: Compare σv, or σvmax, which already has the load factors included, to the factored bearing capacity of the soil (i.e., the ultimate bearing capacity for the soil/rock multiplied by an appropriate resistance factor). The factored bearing capacity (resistance) should be greater than or equal to the factored bearing stress. That is: σv < φbcqult where, qult is the unfactored ultimate bearing capacity for the appropriate limit state and φbc is the resistance factor. Note that qult will be the same for the strength and extreme event limit states. In general, a resistance factor of 1.0 should be used for bearing capacity at the extreme event limit state. See Table 9.9.5-2 for resistance factors for the strength limit state. Bearing capacity for the strength and extreme event limit states should be calculated considering the effects of soil frictional and cohesive resistance, footing dimensions and shape, footing embedment, and slope of the ground in front of the footing. The Geotechnical Branch will calculate the footing bearing capacity using either the AASHTO LRFD specifications, Article 10.6.3.1, or other widely accepted methods provided in the literature. Load inclination factors will not, in general, be considered in the determination of bearing capacity. The Geotechnical Branch may limit the ultimate bearing capacity based on the geotechnical engineering experience available for the given geological formation. C. Sliding Stability for Footings — Strength and Extreme Event Limit States The factored sliding resistance is comprised of a frictional component (φτ Qτ) and a passive earth pressure component (φep Qep). The frictional component acts along the base of the footing, and the passive component acts on the vertical face of the buried footing element. Factored Sliding Resistance, QR = φτ Qτ + φep Qep The Strength Limit State, φτ and φep are determined from Table 9.9.5-2. For the Extreme Event Limit State, φτ = 1.0 and φep = 1.0. If passive resistance in front of footing is not dependable due to potential for erosion, scour, or future excavation in front of footing, use φep = 0.0 for the strength and extreme event limit states, and for temperature/shrinkage loads. The Geotechnical Branch should be contacted for assistance to determine if passive resistance should be considered for analysis of sliding stability.
9.9-14
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design Qτ δ δ δ V φ
= = = = = =
Application of LRFD Code to WSDOT Foundation Design (V)tan δ friction angle between the footing base and the soil tan φ for cast-in-place concrete against soil (0.8)tan φ for precast concrete total vertical force on footing angle of internal friction for soil
The factored sliding resistance should be greater than or equal to the factored horizontal applied loads. D. Overturning Stability for Footings — Strength and Extreme Event Limit States Calculate the eccentricity about Point O in Figure 9.9.5-2 or Figure 9.9.5-3 to locate the resultant force, R. Forces and moments resisting overturning are to be considered negative, and minimum load factors should be used (see Table 9.9.5-1). Forces and moments causing overturning are to be considered positive, and maximum load factors should be used for those forces (see Table 9.9.5-1). For strength limit state, keep the resultant force at the base of the footing within the middle 1/2 of the footing dimensions for soil and the middle 3/4 of the footing dimensions for rock. For extreme event limit state and with γEQ = 0, keep the resultant force at the base of footing within the middle 2/3 of the footing dimensions for soil and rock. If γEQ = 1.0, keep the resultant force at the base of the footing within the middle 3/4 of the footing dimensions for soil and rock. Note that for footings subjected to biaxial loading, these eccentricity requirements apply in both directions. E. Overall Stability for Footings — Service and Extreme Event Limit States The Geotechnical branch will evaluate overall stability using modified Bishop, Janbu, Spencer, or other widely accepted slope stability analysis methods. Article 10.5.2 recommends that overall stability be evaluated at the Service I limit state (i.e., a load factor of 1.0) and a resistance factor, φos of 0.65 for slopes which support a structural element. Available slope stability programs produce a single factor of safety, FS. The Geotechnical Branch will continue its past practice of checking overall slope stability to insure that footings designed for a maximum bearing stress equal to the specified service limit state bearing capacity will not cause the slope stability factor of safety to fall below 1.5 (1.1 for extreme event limit state, with service loads and a horizontal acceleration kh equal to 0.5 A). This practice will essentially produce the same result as specified in Article 10.5.2 of the AASHTO LRFD Specifications. The footing loads should be as specified for the Service I limit state for this analysis. If the footing is located on the slope such that the footing load increases slope stability, the Geotechnical Branch will not establish a maximum footing load which is acceptable for insuring overall slope stability (see Figure 9.9.4-3 for example), but will instead ignore the presence of the footing to evaluate overall stability.
Example Where Footing Contributes to Instability of Slope (left figure) vs. Example Where Footing Contributes to Stability of Slope (right figure) Figure 9.9.5-4
July 2000
9.9-15
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
A resistance factor of 0.9, which is equivalent to a factor of safety of 1.1 in current WSDOT practice, should in general be used for overall stability for the extreme event limit state. F. Resistance Factors for Footing Design — Strength Limit State Resistance Factors for Strength Limit State for Shallow Foundations (adapted from Table 10.5.5-1 of the AASHTO LRFD Specifications) Table 9.9.5-2 Type of Resistance Bearing Capacity
Sliding
Method/Soil/Condition φbc
φτ
φep
9.9-16
Sand - Semi-empirical procedures using SPT data - Semi-empirical procedure using CPT data - Rational Method using φ estimated from SPT data using φ estimated from CPT data
Resistance Factor
0.45 0.55 0.35 0.45
Clay - Semi-empirical procedure using CPT data - Rational Method using shear resistance measured in lab tests using shear resistance measured in field vane tests using shear resistance estimated from CPT data
0.60 0.60 0.50
Rock - Semi-empirical procedure, Carter and Kulhawy (1988)
0.60
Plate Load Test
0.55
Precast concrete placed on sand - using φ estimated from SPT data - using φ estimated from CPT data
0.90 0.90
Concrete cast-in-place on sand - using φ estimated from SPT data - using φ estimated from CPT data
0.80 0.80
Sliding on clay is controlled by the strength of the clay when the clay shear strength is less than 0.5 times the normal stress, and is controlled by the normal stress when the clay shear strength is greater than 0.5 times the normal stress (see Figure 10.6.3.3-1 in AASHTO LRFD specifications, which is developed for the case in which there is at least 150 mm of compacted granular material below the footing). Clay (where shear resistance is less than 0.5 times normal pressure) - Using shear resistance measured in lab tests - Using shear resistance measured in field tests - Using shear resistance estimated from CPT data Clay (where the resistance is greater than 0.5 times normal pressure)
0.85 0.85 0.80 0.85
Soil on soil
1.00
Passive earth pressure component of sliding resistance
0.50
0.50
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
G. Design of Footings at the Service Limit State The service limit state bearing capacity, qserv, will be a settlement limited value (typically 1 inch, but may be greater for long spans, simple spans, or relatively flexible structures). The method used to determine the service limit state bearing capacity will depend on the soil type. The Geotechnical Branch will use the AASHTO specifications or an appropriate textbook to select a settlement estimating method. The Meyerhof approach (see discussion under “Footing Bearing Stress and Capacity — Strength and Extreme Limit States”) should be used to calculate the footing bearing stress, except that service limit state load factors should be used. For immediate settlement (not time dependent), both permanent dead load and live load should be considered for sizing footings for the service limit state. For time dependent settlement (e.g., on clays), only the permanent dead loads should be considered. σv < φqserv, where qserv is the unfactored service limit state bearing capacity and φ is the resistance factor. In general, a resistance factor of 1.0 should be applied to the bearing capacity at the service limit state. Design of a footing for overall slope stability at the service limit state was covered previously. H. What the Geotechnical Branch Will Provide to the Bridge Office for LRFD Footing Design To evaluate bearing capacity, the Geotechnical Branch will provide qult and qserv for various effective footing widths likely to be used, and resistance factors for each limit state. The amount of settlement on which qserv is based will be stated. The calculations will assume that qult and qserv are uniform loads applied over effective footing dimensions B’ and L’ (i.e., effective footing width and length ((B or L) - 2e) as determined using the Meyerhof method, at least for soil. For footings on rock, the calculations will assume that qult and qserv are peak loads and that the stress distribution is triangular or trapezoidal rather than uniform. The Geotechnical Branch will also provide embedment depth requirements or footing elevations to obtain the recommended bearing capacity. To evaluate sliding stability and eccentricity, the Geotechnical Branch will provide the following information: • resistance factors for both the strength and extreme event limit states for calculating Qt and Qep • soil parameters of φ, Kp, γ and depth of soil in front of footing to ignore in calculating Qep • φ, Ka, and γ for calculating active force behind footing (abutments only) To evaluate soil response and development of forces in foundations for the extreme event limit state, the Geotechnical Branch will provide foundation soil/rock shear modulus and Poissons ratio (G and µ). These values will typically be determined for shear strain levels of 0.02 to 0.2%, which span the strain levels for typical large magnitude earthquakes. The Geotechnical Branch will evaluate overall stability and provide the maximum (unfactored) footing load which can be applied to the design slope and still maintain an acceptable safety factor (typically 1.5 for the strength and 1.1 for the extreme event limit states, which is the inverse of the resistance factor). A uniform bearing stress as calculated by the Meyerhof method will be assumed for this analysis. An example presentation of the LRFD footing design recommendations to be provided by the Geotechnical Branch is as shown in Tables 9.9.5-3 and 9.9.5-4, and Figure 9.9.5-5.
July 2000
9.9-17
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Example Presentation of Soil Design Parameters for Sliding and Eccentricity Calculations Table 9.9.5-3
Parameter
Abutment Piers
Interior Piers
Soil Unit Weight, γ (soil above footing base level)
X
X
Soil Friction Angle, φ (soil above footing base level)
X
X
Active Earth Pressure Coefficient, Ka
X
X
Passive Earth Pressure Coefficient, Kp
X
X
Coefficient of Sliding, Tan δ
X
X
Example Presentation of Resistance Factors for Footing Design Table 9.9.5-4 Resistance Factor, φ
Bearing
Shear Resistance to Sliding
Passive Pressure Resistance to Sliding
Strength
X
X
X
Service
X
Extreme Event
X
X
X
Limit State
Bearing Capacity
Unfactored strength and extreme event limit states
Service limit state at ___ mm of settlement
Effective Footing Width, B’ Example Presentation of Bearing Capacity Recommendations Figure 9.9.5-5
9.9-18
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design 9.9.6
Application of LRFD Code to WSDOT Foundation Design
Loads and Load Factor Application to Deep Foundation Design Figures 9.9.6-1 and 9.9.6-2 provide definitions and typical locations of the forces and moments which act on deep foundations. Table 9.9.6-1 identifies when to use maximum or minimum load factors for the various modes of failure for the shaft or pile (bearing capacity, uplift, and lateral loading) for each force.
Definition and Location of Forces and Moments for Integral Shaft Column or Pile Bent Figure 9.9.6-1
July 2000
9.9-19
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Definition and Location of Forces and Moments for Pile or Shaft Supported Footing Figure 9.9.6-2 where, qp qs qDD QDD Wnet
= = = = =
Mp or Mt
=
Mn or Ml
=
MEQp or MEQt = MEQn or MEQl =
ultimate end bearing resistance at base of shaft or pile (unit resistance) ultimate side resistance on shaft or pile (unit resistance) ultimate down drag load on shaft or pile (unit load) ultimate down drag load on shaft or pile (total load) unit weight of concrete in shaft minus unit weight of soil times the shaft volume below the groundline (may include part of the column if the top of the shaft is deep due to scour or for other reasons structural static moments applied to footing, calculated at bottom of column (parallel or transverse to pier orientation, respectively) structural static moments applied to footing, calculated at bottom of column (normal or longitudinal to bridge, respectively) structural seismic moments applied to footing, calculated at bottom of column (parallel or transverse to pier orientation, respectively) structural seismic moments applied to footing, calculated at bottom of column (normal or longitudinal to bridge, respectively)
All other forces are as defined for Figures 9.9.5-2 and 9.9.5-4 for footings.
9.9-20
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design Selection of Maximum or Minimum Deep Foundation Load Factors for Various Modes of Failure for the Strength Limit State Table 9.9.6-1 Load Factor
Load
Bearing Stress (ec, sv)
Uplift
*Lateral Loading
DLv
DCmax, DWmax
DCmin, DWmin
DCmax, DWmax
LLv
Use transient load factor (e.g., LL)
Use transient load factor (e.g., LL)
Use transient load factor (e.g., LL)
tp, tt, tn t1
Use DCmax, DWmax for causing forces, DCmin, DWmin for resisting forces
Use DCmax, DWmax for causing forces
DCmax, DWmax
Mp, Mt, Mn, M1
Use DCmax, DWmax for causing moments, DCmin, DWmin for resisting moments
Use DCmax, DWmax for causing moments
Use DCmax, DWmax for causing moments
Ws, Wtoe
EVmax
EVmin
EVmax
Wnet
DCmax
DCmin
N/A
QDD
DDmax
Treat as resistance, and use appropriate resistance factor
N/A
Ft
EHmax
Use EHmax if causes uplift
EHmax
Fq
LS
Use LS if Fq causes uplift
LS
q
Use transient load factor (e.g., LL)
Set = 0
Use transient load factor (e.g., LL)
Use unfactored loads to get force distribution in structure, then factor the resulting forces for final structural design. All forces and load factors are as defined previously.
July 2000
9.9-21
BRIDGE DESIGN MANUAL Criteria Substructure Design 9.9.7
Application of LRFD Code to WSDOT Foundation Design
Drilled Shaft Design Figure 9.9.7-1 provides a flowchart which illustrates the design process and the interaction between the structural and geotechnical engineers needed for shaft design.
▼ 2(GT). Determine soil properties for foundation design, liquefaction potential, and resistance factors in consideration of the soil property uncertainty and the method selected for calculating nominal resistance
▼
1(GT). Determine depth of scour, if present (with help of Hydraulic Engineer)
▼ ▼
1(ST). Determine bridge geometry, pier locations, column diameter, and foundation top
2(ST). Determine loads applied to foundation top, including lateral earth pressure loads for abutments, through structural analysis and modeling as well as shaft lateral load analysis ▼ 3(ST). Determine depth, diameter, and nominal shaft resistance needed to support the unfactored applied loads at the strength limit state ▼ 3(ST). Determine depth, diameter, and nominal shaft resistance needed to support the unfactored applied loads at the strength limit state
▼ 4(GT). Determine nominal single shaft resistance at the strength and extreme limit states as function of depth, for likely shaft diameters needed, considering shaft constructability
▼ 5(ST). Reevaluate foundation stiffnesses, and rerun structural modeling to get new load distribution for foundations. Reiterate if loads from lateral shaft analysis do not match foundation top loads from structural modeling within 5%
▼ 6(ST). Provide estimate of settlement limited resistance (service state) for shaft/shaft group, or foundation depth required to preclude unacceptable settlement
▼
▼ 3(GT). Determine active, passive, and seismic earth pressure parameters as needed for abutments
▼ 5(GT). Estimate downdrag loads, if present
9(GT). Evaluate the shaft/shaft group for nominal resistance at the strength and extreme limit states, and settlement/ resistance at the service limit state
▼ 6(ST). Factor the loads, and adjust the shaft size or depth as needed to resist applied factor loads, both lateral and vertical
▼ 10(GT). Verify estimated tip elevation and shaft nominal resistance from Step 6(ST), as well as the specified tip elevation from the greatest depth required to meet uplift, lateral load, and serviceability requirements; if significantly different than what was provided in Step 6(ST), have structural model and foundation design reevaluated
▼ 7(ST). Check the minimum shaft depth required to resist factored uplift loads and to resist lateral loads within acceptable deformations
▼
▼ 8(GT). Determine P-Y curve parameters for shaft lateral load analysis
GT: ST:
▼ 8(ST). Design the foundation (and walls for abutment)
▼
7(GT). Determine nominal uplift resistance for shafts as function of depth
▼ 9(ST). Develop contract specifications
Geotechnical Engineer Bridge Engineer
Design Flowchart for Shaft Foundation Design Figure 9.9.7-1
9.9-22
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
A. Drilled Shaft Capacity — Strength and Extreme Event Limit States The factored capacity must be greater than the total factored vertical load applied to the shaft. Factored capacity, QR = φqp Qp + φqs Qs (strength and extreme event limit states) where, Qp Qs Ap As
= = = =
qp Ap qs A s end bearing area side area
The unit shaft end bearing and skin friction resistance will be determined by the Geotechnical Branch using an appropriate static analysis method, such as provided in the AASHTO LRFD specifications, Article 10.8.3, or determined from load test results. φqp and φqs are determined from Table 9.9.7-1 for strength limit state conditions. φqp and φqs are equal to 0.90 to 1.0 for the extreme event limit state, depending on the confidence in the soil parameters (typically, a resistance factor of 0.9 for φqp will typically be used where a column is supported by a single shaft). Qp and Qs are the same for both the strength and extreme event limit states. Note that Qs is a total nominal resistance. The AASHTO LRFD specifications treats this net shaft weight, which is the weight of the average minus the weight of the soil volume removed to construct the shaft, as a dead load, in which a load factor of 1.25 is applied. Past WSDOT practice has been to subtract the net shaft weight directly from the shaft capacity. To correctly apply the AASHTO LRFD specifications, this past practice will not be used. Therefore, for LRFD, the structural designer must calculate the net shaft weight (typically, a unit net weight of 50 pcf is sufficiently conservative) and add that net weight to the applied foundation dead load. Articles 10.8.3.3.2 and 10.8.3.4.3 in the current AASHTO specifications require Qp to be reduced for shaft diameters greater than 1.91 m (6.25 ft) in clay and 1.27 m (4.17 ft) in sand, respectively. Since the intent of this correction is to crudely account for settlement, this correction for shaft diameter should not be used if a more detailed analysis of settlement is conducted (see “Service Limit State Design for Drilled Shafts”). Furthermore, it should be noted that qp as determined in Article 10.8.3.4.3 of the AASHTO LRFD specifications, even without this settlement correction factor for shaft diameter, is to some extent settlement limited for shafts in sand and is not a true ultimate value. The reason for this is that a true bearing capacity failure is typically not observed for shafts in sand, but instead deformation simply continues to increase with load. Therefore, the transition from a strength or extreme event limit state to a serviceability limit state is not well defined for shafts in sand. This issue will be evaluated on a case by case basis by the Geotechnical Branch when providing shaft capacity information for all limit states. If downdrag exists, the downdrag force QDD (qDD As) shall be considered as a load rather than a negative resistance for shaft capacity calculations. The downdrag force QDD will be determined by the Geotechnical Branch using an appropriate static shaft skin friction analysis method (see AASHTO LRFD Article 10.8.3.3.1 for a method which can be used). Per Table 9.9.3-2, use a load factor applied to the downdrag force of 1.0. This factored downdrag force, in combination with the other factored applied loads, should be less than or equal to the factored strength and service limit state resistances.
July 2000
9.9-23
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Transient loads should not be considered when downdrag forces are included in the factored load applied to the shaft. Shaft skin friction in the downdrag zone should not be included in the shaft capacity. If downdrag forces are induced by settlement due to liquefaction, downdrag forces shall be considered in the extreme event limit state design of the shaft. Note that the downdrag force during liquefaction may be different than the downdrag force which is applicable during the strength and serviceability limit states, as liquefaction can cause the strength of the soil to change. The downdrag forces calculated for static conditions should not be combined with the downdrag forces resulting from liquefaction when evaluating the extreme event limit state. B. Uplift for Drilled Shafts Factored uplift capacity, Quf = φup qup As = φup Qup where, qup = ultimate unit uplift resistance, φup is as determined from Table 9.9.7-1 for strength limit state conditions, and Qup is the unfactored ultimate uplift capacity. The unit uplift resistance, qup is usually set equal to the unit side friction resistance, qs, for LRFD foundation design, as the resistance factors for uplift in Table 9.9.7-1 already account for the potential for side resistance in uplift being less than the side resistance in compression. If downdrag is likely to occur, either due to long-term settlement or due to liquefaction, the skin friction causing downdrag is considered to be fully available to resist uplift forces. However, the downdrag force is not subtracted from the uplift force. C. Lateral Load Analysis for Drilled Shafts In general, P-Y curves are used for lateral load analysis in the bridge design model to iteratively match deflections and load distributions between the various bridge components, considering the soil response, to insure stability of the bridge. The maximum lateral deflection which is considered acceptable may vary from structure to structure. Even though deflections are calculated, service limit state load groups are usually not used for this analysis. In general, only the extreme event load groups are used for lateral load analysis, and a φlat of 1.0 is used. However, strength limit state load groups are sometimes used for this analysis. For the strength limit state, a resistance factor of 1.0 is recommended at this time. Note that in some cases the depth required for shaft fixity based on lateral load analysis may control the shaft depth required rather than bearing capacity or uplift; for example where soft or liquefiable soils are present. Normally, both static and dynamic P-Y curve parameters are provided in the Geotechnical Report. The static parameters represent the soil behavior for short-term transient loads such as wind, ice, temperature, and vessel impact. For earthquake loads, the dynamic and static P-Y curve parameters will be the same if the soils present have a stiffness which does not degrade with time during shaking, such as would occur during liquefaction. If liquefaction can occur, two P-Y analyses for the extreme event limit state should be conducted, one analysis using the static P-Y parameters and the other analysis using the dynamic P-Y parameters. The intent here is to bracket the structure response. Often, the highest acceleration the bridge sees is in the first cycles of the earthquake, and liquefaction tends to occur toward the middle or end of the earthquake. Therefore, early in the earthquake, loads are high, soil-structure stiffness is high, and deflections are low. Later in the earthquake, the soil-structure stiffness is lower and deflections higher. D. Group Effects for Bearing Capacity AASHTO Article 10.8.3.9 applies.
9.9-24
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Resistance Factors for Drilled Shaft Design Resistance Factors for Strength Limit State for Drilled Shaft Foundations (adapted from Table 10.5.5-3 in AASHTO) Table 9.9.7-1 Type of Resistance Bearing Capacity of Single Drilled Shafts
Method/Soil/Condition φqp
φqs
Resistance Factor
Base Resistance in Clay: - Total stress (Reese and O’Niel, 1988)
0.55
Base Resistance in Sand: - SPT method (Reese and O’Niel, 1988)
*0.50
Base Resistance in Rock: - Canadian Geotechnical Society (1985)
0.50
Side Resistance in Clay: - α-method (Reese and O’Niel, 1988)
0.65
Side Resistance in Sand: - β-method (Reese and O’Niel, 1988)
*0.65
Side Resistance in Rock: - Carter and Kulhawy (1988) - Horvath and Kinney (1979) Side and Base Resistance: - Load test Uplift Resistance of Single Drilled Shafts
φup
0.55 0.65 +
0.70-0.80
Clay: - α-method (Reese and O’Niel, 1988) - Belled shafts (Reese and O’Niel, 1988)
0.55 0.50
Sand: - β-method (Reese and O’Niel, 1988)
*0.55
Rock: - Carter and Kulhawy (1988) - Horvath and Kinney (1979) Load Test:
0.45 0.55 +
0.70-0.80
Group Bearing Capacity (block failure)
φqgr
Clay:
0.65
Group Uplift
φupgr
Clay:
0.55
Sand:
0.55
Resistance Lateral Resistance of Shafts and Shaft Groups
φlat
Clay, sand, and rock:
*1.0
*The AASHTO specifications currently do not provide bearing capacity resistance factors in sand and factors for lateral loading. For φlat, the value used will depend on the confidence in the soil parameters. These resistance factors should be considered to be tentative until additional research and comparative designs are accomplished. +
For shaft load tests, the number of load tests required will depend on the uniformity of the soil/rock conditions and whether or not a well defined bearing stratum is present. Assuming that an appropriate number of load tests are conducted, use the largest resistance factor in the specified range for very uniform conditions or for a well defined and highly resistant bearing stratum, and use the lowest resistance factor in the range for nonuniform conditions or a poorly defined bearing stratum.
July 2000
9.9-25
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
E. Group Effects for Uplift AASHTO Article 10.7.3.7.3 applies. F. Group Effects for Lateral Loads P-Y curves are usually derived considering only a single foundation element. To account for group effects, multiply the modulus of subgrade reaction, k, by the appropriate efficiency factor as provided in Table 9.9.7-2, or as specified in the Geotechnical Report. Loading direction and spacing are as defined in Figure 9.9.7-2. Group Efficiency Reduction Factors for Foundation Element Groups Subjected to Lateral Load Table 9.9.7-2 Foundation Element Spacing, Center-toCenter, in Direction of Applied Loading
Efficiency Reduction Factor for Multiple Row Groups, or in Direction Parallel to Single Row
Efficiency Reduction Factor for Single Row Groups for Loading Direction Perpendicular to Row
8b
1.0
1.0
6b
0.9
1.0
5b
0.8
1.0
4b
0.65
0.9
3b
0.5
0.8
2b
0.4
0.6
Definition of Loading Direction and Spacing for Group Effects Figure 9.9.7-2
9.9-26
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
The soil strength parameters are also reduced to account for group effects. For cohesive soils, multiply the soil cohesion, C, directly by the appropriate group reduction factor from Table 9.9.7-2 or as specified in the Geotechnical Report. For granular soils (sands, gravels), multiply the normalized resistance identified in Figure 9.9.7-3 by the appropriate group reduction factor to determine the reduced friction angle. Use the following steps to accomplish this: 1.
Determine the normalized resistance for each soil layer at the friction angle for that soil layer provided in the Geotechnical Report (e.g., for φ = 36o, normalized resistance = 61).
2.
Multiply the normalized resistance determined in Step 1 by the group efficiency reduction factor based on the foundation element spacing (e.g., if the spacing is 3b, the reduction factor is 0.5 and the normalized resistance accounting for group effects is 32).
3.
Based on the reduced normalized resistance, determine the soil friction angle accounting for group effects (e.g., at a normalized resistance of 32, the soil friction angle is 31o).
4.
Use this reduced φ, in combination with the reduced modulus of subgrade reaction, k, to determine the P-Y curve accounting for group effects.
Normalized Resistance as a Function of Soil Friction Angle for Lateral Capacity Determination Figure 9.9.7-3 where, Normalized Resistance = Ps/bγX = Ka(tan8B - 1) + Ko(tan4B)(tanφ) φ
July 2000
=
Soil friction angle
Ps =
Soil resistance on section of foundation element
b
=
Foundation element diameter
γ
=
Soil unit weight
X
=
Depth to section of foundation element
B
=
45o + φ/2
Ka =
tan2 (45o-φ/2)
Ko =
1 - sin φ
9.9-27
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
G. Service Limit State Design for Drilled Shafts The service limit state shaft capacity, Qserv, will be a settlement limited value (typically 0.5 to 1 inch, but may be greater for long spans, simple spans, or relatively flexible structures). See the AASHTO LRFD specifications, Article 10.8.2.3, which provides the method published by Reese and O’Neill, 1988, to estimate the side friction and end bearing mobilized for a specified total settlement for a single shaft. Typically, the Geotechnical Branch will be using this method to estimate vertical deflection of shafts, where applicable. For immediate settlement (not time dependent), which is the type of settlement addressed by the Reese and O’Neill method, both permanent dead load and live load should be considered. For time dependent settlement (e.g., on clays for analysis of shaft groups which are primarily frictional in nature), only the permanent dead loads should be considered. Note that this method was developed for predicting immediate settlement for shafts in clay or in sand. This method may be overly conservative for the very dense glacially consolidated soils often encountered in WSDOT shaft installations, since this method was based on settlement limited behavior in soils which were not as dense as state of Washington glacially overridden soils. The Geotechnical Branch will evaluate the settlement potential of drilled shafts considering the amount of skin friction and end bearing mobilized for service limit state design. Factored bearing capacity at a specified settlement, QRserv = φservp Qpserv + φservs Qsserv (service limit state), where, Qpserv = qpserv Ap Qsserv = qsserv As qpserv
= end bearing resistance at base of shaft (unit resistance) for a specified settlement
qsser
= side resistance on shaft (unit resistance) for a specified settlement
Ap
= end bearing area,
As
= side area,
In general, a resistance factor of 1.0 should be used for shaft capacity at the service limit state (φservb and φservs). H. What Geotechnical Branch Will Provide to Bridge Office for LRFD Shaft Design To evaluate bearing capacity, the Geotechnical Branch will provide as a function of depth and at various shaft diameters the unfactored ultimate bearing capacity for end bearing, Qp, and side friction, Qs, used to calculate QR, for strength and extreme event limit state calculations (see example figures below). For the service limit state, the unfactored bearing capacity at a specified settlement, typically 0.5 or 1.0 inch, Qpserv (mobilized end bearing) and Qsserv (mobilized side friction) will be provided as a function of depth and shaft diameter. See Figure 9.9.7-4 for an example of the capacity information that would be provided. A similar set of curves, for the strength and extreme event limit states, will also be provided for uplift capacity, Qup. Qup will be reduced to account for scour or liquefaction/ weakening.
9.9-28
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
In most cases, Qult and Qup for the strength, extreme event II and extreme event I limit states will be the same, as loss of skin friction due to liquefaction downdrag will be taken into account separately. However, if soils are present which weaken but do not liquefy during an earthquake, a separate curve for the extreme event I limit state may be needed. Note that the side friction bearing capacities provided in these figures will be a total nominal resistance, in that the net weight of the shaft below the final groundline will not already be subtracted out of the side friction capacity. Resistance factors for bearing capacity for all limit states will also be provided, as illustrated in Table 9.9.7-3. If downdrag is an issue, the ultimate downdrag load, QDD, as a function of shaft diameter will be provided, as well as the depth zone of the shaft which is affected by downdrag, the downdrag load factor, and the cause of the downdrag (settlement due to vertical stress increase, liquefaction, etc.). If liquefaction occurs, the reduction in side friction resistance, Qs, to be subtracted off of the ultimate side friction capacity plots will be provided. See example tables below. Example Presentation of Resistance Factors for Shaft Design Table 9.9.7-3 Resistance Factor Limit State
Skin Friction, Qs
End bearing, Qp
Uplift, Qup
Strength
X
X
X
Service
X
X
Extreme Event
X
X
X
If lateral loads imposed by special soil loading conditions such as landslide forces are present, the ultimate lateral soil force or stress distribution, and the load factors to be applied to that force or stress, will be provided. The Geotechnical Branch will also provide group reduction factors for bearing capacity and uplift if necessary, as well as the associated resistance factors. The Geotechnical Branch will continue to provide P-Y curve data as a function of depth as has been done in the past. Resistance factors for lateral load analysis will not be provided, as the lateral load resistance factors will typically be 1.0.
July 2000
9.9-29
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design Example Presentation of Downdrag Loads Table 9.9.7-4 QDDs, Static Conditions
QDDliq Due to Liquefaction
Pier No.
Shaft Dia = __
Shaft Dia = __
Shaft Dia = __
Shaft Dia = __
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Example Presentation of Skin Friction Loss Due to Downdrag or Scour Table 9.9.7-5 Qs Loss to be Applied to Figure 9.9.6-3 Due to Static Downdrag or Scour for Strength Limit Qult
Qs Loss to be Applied to Figure 9.9.6-3 Due to Liquefaction Downdrag for Extreme Event Limit Qult
Pier No.
Shaft Dia = __
Shaft Dia = __
Shaft Dia = __
Shaft Dia = __
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
9.9-30
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Qs (unfactored)
QQpb (unfactored)
Shaft Diameter = ___
Shaft Diameter = ___
Strength and Extreme Limit States Elevation or Depth
Elevation or Depth
(a separate curve may be needed for the extreme event I limit state in some cases)
Strength and Extreme Limit States
Service Limit Service Limit State at State at ___ ___(in.) of Settlement of
Service Limit Service Limit State at ___ (in.) State at ___ of Settlement of
Typical Shaft Total Bearing Capacity Plots (All Limit States) Figure 9.9.7-4
9.9.8
Pile Foundation Design The objective of pile foundation design is to determine the following: • pile capacity, • pile size, • pile type, • size of the pile group required to resist the structural loads, • estimated pile quantity needed, • minimum tip elevation required, and • driveability of the piles to meet the design requirements. The pile foundation design should also include characterization of the pile foundation for purposes of modeling the overall structure, especially for seismic design.
July 2000
9.9-31
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Figure 9.9.8-1 provides a flowchart which illustrates the design process and the interaction between the structural and geotechnical engineers needed for pile foundation design.
▼ 2(GT). Determine soil properties for foundation design, liquefaction potential, and resistance factors in consideration of the soil property uncertainty and the method selected for calculating nominal resistance
▼
1(GT). Determine depth of scour, if present (with help of Hydraulic Engineer)
▼ ▼
1(ST). Determine bridge geometry, pier locations, and foundation top
2(ST). Determine loads applied to foundation top, including lateral earth pressure loads for abutments, through structural analysis and modeling as well as pile lateral load analysis
9(GT). Evaluate the pile group for nominal resistance at the strength and extreme limit states, and settlement/ resistance at the service limit state
▼ 3(ST). Determine the number of piles required to support the unfactored applied loads at the strength limit state, and their estimated depth ▼ 3(ST). Determine the number of piles required to support the unfactored applied loads at the extreme event limit state, and their estimated depth
▼ 4(GT). Select best pile types, and determine nominal single pile resistance at the strength and extreme limit states as function of depth, estimating pile sizes likely needed, and establishing maximum acceptable pile nominal resistance
▼ 5(ST). Reevaluate foundation stiffnesses, and rerun structural modeling to get new load distribution for foundations. Reiterate if loads from lateral pile analysis do not match foundation top loads from structural modeling within 5%
▼ 5(GT). Estimate downdrag loads, if present
▼ 6(ST). Factor the loads, and adjust size of pile group or the pile capacities and estimated depths as needed to resist applied factored loads
▼
▼ 3(GT). Determine active, passive, and seismic earth pressure parameters as needed for abutments
▼ 10(GT). Verify estimated tip elevation and pile nominal resistance from Step 6(ST), as well as minimum tip elevation from the greatest depth required to meet uplift, lateral load, and serviceability requirements
▼ 6(ST). Provide estimate of settlement for pile/pile group, or foundation depth required to preclude unacceptable settlement
▼ 7(ST). Check the minimum pile depth required to resist factored uplift loads and to resist lateral loads within acceptable deformations
▼ 11(GT). Based on minimum tip elevation and pile diameter needed, determine need for overdriving and driveability of pile as designed; if not driveable, reevaluate pile foundation design and structural model
▼
▼ 8(GT). Determine P-Y curve parameters for pile lateral load analysis
GT: ST:
▼ 8(ST). Design the foundation (and walls for abutment)
▼
7(GT). Determine nominal uplift resistance for piles as function of depth
▼ 9(ST). Develop contract specifications, obtaining pile quantities from estimated pile depths, minimum pile capacity required, minimum tip elevations, and overdriving required from design
Geotechnical Engineer Bridge Engineer
Design Flowchart for Pile Foundation Design Figure 9.9.8-1
9.9-32
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
A. Pile Type, Pile Size, Bearing Capacity, and Estimated Tip Elevation — Strength and Extreme Event Limit States First, determine the feasible ultimate pile capacity, Qult, for the soil at the site, and determine the desired pile type and diameter. This ultimate capacity should be unfactored and based on static capacity calculations or experience with a given soil deposit. See the Federal Highway Administration manual FHWA-HI-97-013 “Design and Construction of Driven pile Foundations,” 1997, for examples of static analysis methods for piles. The feasible ultimate pile capacity may also be controlled by the structural capacity of the pile, especially if the pile will be driven to a very hard bearing stratum (e.g., driven to refusal). Determine the structural capacity of the pile per Article 10.7.4 in the AASHTO specifications. In lieu of more detailed structural analysis, the general guidance on pile types, sizes, and ultimate capacities provided in Table 9.9.8-1 can be used to select pile sizes and types for analysis. The Geotechnical Branch may also limit the ultimate pile capacity for a given pile size and type driven to a given soil/rock bearing unit based on experience with the given soil/rock unit. The maximum capacity allowed in that given soil/rock unit may be increased by the Geotechnical Branch per mutual agreement with the Bridge and Structures Office if a pile load test is performed. Typical Pile Types and Sizes for Various Ultimate Pile Capacities Table 9.9.8-1 Pile Type and Diameter, in in. Ultimate Pile Capacity in tons
Closed End Steel Pipe/Cast-in-Place Concrete Piles
*Precast, Prestressed Concrete Piles
Steel H-Piles
Timber Piles
60 tons
-
-
-
See WSDOT Standard Specs.
120 tons
-
-
-
See WSDOT Standard Specs.
165 tons
12 in.
13 in.
-
-
210 tons
14 in.
16 in.
12 in.
-
300 tons
18 in. nonseismic areas (Category A), 24 in. seismic areas (Category B, C, and D)
18 in.
14 in.
-
450 tons
24 in.
Project Specific
Project Specific
-
*Precast, prestressed concrete piles are generally not used for highway bridges, but are more commonly used for marine work.
July 2000
9.9-33
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Select the construction quality control method to be used (e.g., driving formula, wave equation, Pile Driving Analyzer, etc.), and the resistance factors associated with the selected method, φdyn. Determine the total factored load to be applied to the pier in question (strength and extreme event limit states). Note that the actual distribution of that load to the piles will depend on the number of piles in the group as well as where they are located within the group geometry. The factored load per pile, Loadp, is determined as follows: Loadp =
ΣγiQi n
+
(ΣγiMi)c I
where, Mi = the moment at the base of the column resulting from the forces applied to the column (i.e., dead load, live load, seismic load, etc.) C
= the distance between the centroid of the pile group and the center of the pile under consideration
I
= moment of inertia of the pile group
N
= number of piles in the pile group
Other variables are as defined previously. Determine the number of piles required in the pile group such that the factored load in any pile in the group is not greater than the factored resistance. Use the resistance factor for the construction quality control method selected previously, that is, QR = φdyn x Qult. Qult is the feasible ultimate pile capacity. Do not use the above method if the pile is being driven to a specified tip elevation and the pile capacity is not being determined in the field using a driving criteria which is based on a pile penetration resistance (i.e., any dynamic method). In this case use the resistance factor for the static analysis method used to determine the pile capacity. In this case, QR = φqp Qp + φqs Qs (strength and extreme event limit states). Check all limit states, and determine the pile group size using the limit state which requires the most piles for the specified ultimate capacity. Note that φdyn, φqp, and φqs are all equal to 0.9 to 1.0 for the extreme event limit state, depending on the confidence in the soil parameters (AASHTO specifications recommend that 1.0 be used). The pile weight will be neglected in most cases, but if it is to be considered, it is to be treated as a load as is done for safts (see Section 9.9.7A). Qp and Qs are the same for both the strength and extreme event limit states. If downdrag exists, the downdrag force QDD (qDD As) shall be considered as a load rather than a negative resistance for pile capacity calculations. The downdrag force QDD will be determined by the Geotechnical Branch using an appropriate static pile skin friction analysis method (see FHWA manual on the design of driven pile foundations mentioned previously). Per Table 9.9.3-2, use a load factor applied to the downdrag force of 1.0. This factored downdrag force, in combination with the other factored applied loads, should be less than or equal to the factored strength and service limit state resistances. Transient loads should not be considered when downdrag forces are included in the factored load applied to the pile for service and strength limit state calculations. Pile skin friction in the downdrag zone should not be included in the pile ultimate capacity.
9.9-34
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
If downdrag forces are induced by settlement due to liquefaction, downdrag forces shall be considered in the extreme event limit state design of the pile. Note that the downdrag force during liquefaction may be different than the downdrag force which is applicable during the strength and serviceability limit states, as liquefaction can cause the strength of the soil to change. The downdrag forces calculated for static conditions should not be combined with the downdrag forces resulting from liquefaction when evaluating the extreme event limit state. Figure 9.9.8-2 illustrates how downdrag loads and loss of resistance is to be handled. When downdrag occurs (see Figure 9.9.7-1), the ultimate pile capacity needed is determined as follows: Qult = Loadp/φdyn + QDD + Qsdd For the strength and extreme event limit states, if the soil is characterized as cohesive, the pile group capacity should also be checked for the potential for a “block” failure. Article 10.7.3.10 in the AASHTO specifications applies. See Table 9.9.8-2 to determine the appropriate resistance factor for the strength limit state. Use a resistance factor of 0.9 to 1.0 for the extreme event limit state. Compare the factored loads for each limit state to the factored block resistance. If a block failure appears likely, increase the group size so that a block failure is prevented. For estimating pile quantities, develop unfactored, ultimate pile capacity versus estimated depth curves using a static analysis method (see Figure 9.9.8-2 for example). The Geotechnical Branch may adjust the estimated depth for a given pile capacity based on experience with the soil/rock deposit in question and professional judgment. Determine the estimated pile length, Dest., for the desired ultimate capacity, Qult, from this pile capacity versus depth curve for the purpose of estimating pile quantities. Make sure that Qult is greater than or equal to the factored load per pile divided by the appropriate resistance factor, that is: Qult ≥ Loadp/φdyn + QDD + Qsdd For the construction specifications, use the estimated pile length determined as illustrated in Figure 9.9.7-1 for the contract pile quantity, and use Qult (unfactored) for the pile capacity which is inserted into the driving formula, wave equation, etc., to determine the penetration resistance required to accept the pile. Note: The estimated pile length will be reasonably accurate if the bias, λR, for the static analysis method used to estimate pile lengths and the feasible ultimate pile capacity is approximately the same as the bias, λR, for the dynamic analysis method used to determine the factored pile capacity. If the biases for the two methods are not the same, the estimated pile length could be in error for a given level of risk. If the coefficients of variation for the two methods are also significantly different for the two methods, this could accentuate the possible error for a given level of risk. For example, if the dynamic formula tends to predict an average capacity which is approximately the same as the capacity measured from a pile load test, but the static analysis method tends to under-predict the pile capacity measured from a pile load test, the pile depth predicted using the static analysis method illustrated in Figure 9.9.8-2 is likely to be too deep. Note that this is not likely to be an issue when driving the pile to a well defined very dense stratum such as glacially loaded till or bedrock. This pile length prediction accuracy is mainly a concern for friction piles. Therefore, some engineering judgment based on experience may be needed to estimate pile quantities with reasonable accuracy.
July 2000
9.9-35
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Loadp φdyn
Loadp φdyn
Example Ultimate Pile Capacity Versus Depth Curve for Estimating Pile Lengths Figure 9.9.8-2
QSdd = skin friction which must be overcome during driving through downdrag/liquefaction/scour zone Loadp + QDD = ultimate pile capacity needed to resist all applied axial loads per pile, including downdrag φdyn Loadp
= factored load per pile, not including downdrag
QDD
= downdrag load per pile
n
= number of piles in pile group for pier
Dest.
= estimated pile length needed to obtain desired ultimate capacity
9.9-36
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
B. Determination of Minimum Pile Tip Elevations Determine the minimum pile depth required to meet settlement, lateral deflection/capacity, and uplift requirements. This would become the minimum pile tip elevation requirement for the contract specifications. Note that lateral loading and uplift requirements may influence (possibly increase) the number of piles required in the group if the capacity available at a reasonable minimum tip elevation is not adequate. This will depend on the soil conditions and the loading requirements. For example, if the upper soil is very soft or will liquefy, making the minimum tip elevation deeper is unlikely to improve the lateral response of the piles enough to be adequate. Adding more piles to the group or using a larger pile diameter to increase the pile stiffness may be the only solution. The various analyses required to establish the minimum tip elevations needed (if minimum tip elevations are in fact needed), are as follows: 1.
Uplift for Piles For the strength and extreme limit states, for the pile group size and geometry already determined, calculate for the structure the uplift capacity per pile needed using factored loads. Calculate the uplift resistance available using static analysis methods and using resistance factors appropriate for the static analysis method used, for both limit states. Do this as a function of pile depth. Therefore, Factored uplift capacity, Quf = φup qup As = φup Qup where, qup = ultimate unit uplift resistance, As is the pile side area, φup is as determined from Table 9.9.7-2 for strength limit state conditions, and Qup is the unfactored ultimate uplift capacity. The unit uplift resistance, qup is usually set equal to the unit side friction resistance, qs, for LRFD foundation design, as the resistance factors for uplift in Table 9.9.7-2 already account for the potential for side resistance in uplift being less than the side resistance in compression. If downdrag is likely to occur, either due to long-term settlement or due to liquefaction, the skin friction causing downdrag should be considered to be fully available to resist uplift forces. However, the downdrag force is not subtracted from the uplift force. From these calculations, determine the depth required to obtain the required factored uplift capacity.
2.
Lateral Load Analysis for Piles “Lateral Load Analysis for Drilled Shafts” applies.
3.
Pile Group Bearing Capacity and Settlement (Service Limit State) For the service limit state, compare the factored load to the maximum group capacity per AASHTO Articles 10.7.2.1 and 10.7.2.3 to determine the pile depth which will result in the desired maximum settlement. Treat the pile group as an equivalent footing as described in Articles 10.7.2.1 and 10.7.2.3 in the AASHTO Specifications, and calculate the settlement of the group. Do this to get the minimum depth required to prevent the settlement criteria from being exceeded.
4.
Group Effects for Uplift AASHTO Article 10.7.3.7.3 applies.
5.
Group Effects for Lateral Loads “Group Effects for Lateral Loads” under “Shaft Design” applies.
July 2000
9.9-37
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
C. Resistance Factors for Pile Foundation Design Resistance Factors for Strength Limit State for Pile Foundations (adapted from Table 10.5.5-2 in AASHTO LRFD specifications) Table 9.9.8-2 Type of Resistance Bearing Capacity of Single Piles (static analysis methods)
Method/Soil/Condition φqs
Skin Friction in Clay: - α-method (Tomlinson, 1987) - β-method (Esrig and Kirby, 1979) - λ-method (Vijayvergiya and Focht, 1972) Skin Friction in Sand: - SPT Method (Meyerhof) - CPT Method - Nordlund Method
φqp
Resistance Factor 0.70 0.50 0.55 0.45 0.55 + 0.55
End Bearing in Clay and Rock: - Clay (Skempton, 1951) - Rock (Canadian Geotechnical Society, 1985)
0.70 0.50
End Bearing in Sand: - SPT Method (Meyerhof) - CPT Method - Thurman’s Method
0.45 0.55 + 0.55
φqs, φqp
Side and Base Resistance: - Load test
*0.70-0.80
Bearing Capacity of Single Piles (dynamic analysis methods)
φdyn
Side Resistance and End Bearing, All Soils: - WSDOT driving formula, per Standard Specifications - ENR driving formula - Wave Equation, without PDA - Wave Equation with PDA (PDA used on one pile/ pier and 2 to 5% of the piles) - PDA with CAPWAP (min. one pile/pier and 2 to 5% of the piles)
0.50 0.25 ‡0.50 ‡0.60 ‡0.60-0.75
Uplift Resistance of Single Piles
φup
a-method (clay) b-method (clay) l-method (clay) SPT-method (Meyerhof method for sand) CPT-method (sand) Nordlund Method (sand) CAPWAP Uplift Load Test
0.60 0.40 0.45 0.35 0.45 + 0.45 ? *0.70-0.80
Block Failure
φqgr
Clay
0.65
Group Uplift Resistance
φupgr
Sand Clay
0.55 0.55
Lateral Pile Resistance
φlat
Clay, sand, and rock (single piles and groups):
#
1.0
*For the load test resistance factor, the values shown are more conservative than as provided in the AASHTO specifications. They have been adjusted based on calibration to current WSDOT practice (FS = 2 if load test is conducted). Note that the number of load tests required will depend on the uniformity of the soil/rock conditions and whether or not a well defined bearing stratum is present. Assuming that an appropriate number of load tests are conducted, use the largest resistance factor in the specified range for very uniform conditions or for a well defined and highly resistant bearing stratum, and use the lowest resistance factor in the range for nonuniform conditions or a poorly defined bearing stratum. ‡For the wave equation and PDA resistance factors, the values shown are more conservative than as provided in the AASHTO specifications. They have been adjusted based on calibration to current WSDOT practice (FS = 2.25 if wave equation and PDA are conducted, and FS = 2.75 if wave equation without PDA is used). For PDA with CAPWAP, calibration of CAPWAP results to pile load test results indicate that a resistance factor as high as 0.75 to 0.8 could be used. However, that calibration assumes that a CAPWAP is performed on every pile, or the soil/rock conditions are perfectly uniform, which in actual applications is never the case. Assuming that the number of piles as specified in the table are tested using a PDA/CAPWAP, use the largest resistance factor in the specified range for very uniform conditions or for a well defined and highly resistant bearing stratum, and use the lowest resistance factor in the range for nonuniform conditions or a poorly defined bearing stratum. These resistance factors for pile capacity should be considered to be tentative until additional research and comparative designs are accomplished +
The approach defined above for the use of load test data or PDA/wave equation was also used to determine resistance factors for the Nordlund and Thurman pile capacity methods (current WSDOT practice is to use FS = 2.5 with these methods). Furthermore, statistical analysis provided by the FHWA course manual “Load and Resistance Factor Design (LRFD) for Highway Bridge Substructures,” 1998, for the Nordlund method confirms that resistance factors for this method should be on the order of 0.55 to 0.6.
#
For φlat, the value used will depend on the confidence in the soil parameters.
9.9-38
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
D. Determination of Pile Driveability If the required minimum tip elevation is deeper than the penetration depth estimated to obtain the desired pile capacity (Qult), the pile will need to be overdriven. Estimate the amount of overdrive (i.e., maximum driving capacity) required using the unfactored pile capacity versus depth curve as illustrated in Figure 9.9.7-3, but instead using the minimum tip elevation to determine the ultimate pile capacity at the minimum tip elevation. This will yield the maximum driving resistance per the WSDOT Standard Specifications to be used to size the pile hammer and to determine the minimum pile wall thickness. The pile hammer and minimum pile wall thickness are sized so that maximum driving stresses are not exceeded, and pile damage during driving is prevented. In this case, a preliminary wave equation analysis should be conducted during design by the Geotechnical Branch to evaluate potential pile driveability, and to set minimum pile wall thickness and minimum hammer energy requirements for the contract specifications as appropriate. E. What Geotechnical Branch Will Provide to Bridge Office for LRFD Pile Design To evaluate pile capacity, the Geotechnical Branch will provide information regarding pile capacity using one of the following two approaches: 1.
A plot of the unfactored ultimate bearing capacity (Qult) as a function of depth for various pile types and sizes for strength and extreme event limit state calculations would be provided. This design data would be used to determine the feasible ultimate pile capacity, the estimated depth for pile quantity determination, and the maximum driving resistance required to reach the minimum tip elevation. If scour and/or liquefaction is likely to occur, separate tables will usually be provided which summarize the estimated downdrag loads and capacity losses. Such assumptions/special considerations will also be identified on the plots. See Figure 9.9.8-3 for example of pile data presentation.
2.
Only Qult and the estimated depth at which it could be obtained, and tabulated capacity reductions necessary to account for the effects of scour and/or liquefaction, would be provided for one or more selected pile types and sizes.
In most cases, Qult and Qup for the strength, extreme event II, and extreme event I limit states will be the same, as loss of skin friction due to liquefaction downdrag will be taken into account separately. However, if soils are present which weaken but do not liquefy during an earthquake, a separate curve for the extreme event I limit state may be needed. For evaluating uplift, the Geotechnical Branch will provide, as a function of depth, the ultimate unfactored uplift capacity, Qup. This will be provided as a function of depth, or as a single value for a given minimum tip elevation, depending on the project needs, and will be reduced to account for scour and/or liquefaction. Resistance factors will also be provided for strength and extreme event limit states. Resistance factors for bearing capacity for all limit states will also be provided (see Table 9.9.8-2 for an example). If downdrag is an issue, the ultimate downdrag load, QDD, as a function of pile diameter will be provided, as well as the depth zone of the pile which is affected by downdrag, the downdrag load factor, and the cause of the downdrag (settlement due to vertical stress increase, liquefaction, etc.). If liquefaction occurs, the reduction in side friction resistance, Qs, to be subtracted off of the ultimate capacity plots will be provided.
July 2000
9.9-39
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
If lateral loads imposed by special soil loading conditions such as landslide forces are present, the ultimate lateral soil force or stress distribution, and the load factors to be applied to that force or stress, will be provided. The Geotechnical Branch will also provide group reduction factors for bearing capacity and uplift if necessary, as well as the associated resistance factors, but these will be rarely needed. The Geotechnical Branch will continue to provide P-Y curve data as a function of depth as has been done in the past. Two separate tables will typically be provided, one for static properties and one for dynamic properties (see Section 9.9.6C for an explanation on how they are to be used.) Resistance factors for lateral load analysis will not be provided, as the lateral load resistance factors will typically be 1.0. Minimum tip elevations for the pile foundations will be provided as appropriate. Minimum tip elevations will be based on pile foundation settlement, and, if uplift loads are available, the depth required to provide adequate uplift capacity. Minimum pile tip elevations provided in the Geotechnical Report may need to be adjusted depending on the results of the lateral load and uplift load evaluation performed by the Bridge and Structures Office. If adjustment in the minimum tip elevations is necessary, or if the pile diameter needed is different than what was assumed by the Geotechnical Branch for pile capacity design, the Geotechnical Branch should be informed so that pile driveability, as discussed below, can be re-evaluated. Pile driveability will be evaluated at least conceptually for each project, and if appropriate, a wave equation analysis will be performed and the results of the analysis provided in terms of special requirements for hammer size and pile wall thickness, etc. The maximum driving resistance required to reach the minimum tip elevation will also be provided. Note that it will not be possible to obtain the maximum driving resistance from the pile bearing capacity plots mentioned previously if the pile bearing capacities provided in the plots have been reduced to account for scour and/or liquefaction. A separate determination is required to estimate the maximum driving resistance if the pile capacity versus depth plots include the effects of scour or liquefaction. Once the pile analysis and design are completed in the Bridge and Structures Office, the Geotechnical Branch is to be contacted for final reivew ad comment. Example Presentation of Resistance Factors for Pile Design Table 9.9.8-3 Resistance Factor Limit State
9.9-40
Bearing Capacity, Qult
Uplift, Qup
Strength
X
X
Service
X
—
Extreme Event
X
X
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design Example Presentation of Downdrag Loads Table 9.9.8-4 QDDs Static Conditions
QDDliq Due to Liquefaction
Pier No.
Pile Dia = __
Pile Dia = __
Pile Dia = __
Pile Dia = __
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Example Presentation of Skin Friction Loss Due to Downdrag or Scour Table 9.9.8-5 Qs Loss to be Applied to Figure 9.9.8-2 Due to Static Downdrag or Scour for Strength Limit Qult
Qs Loss to be Applied to Figure 9.9.8-2 Due to Liquefaction Downdrag for Extreme Event Limit Qult
Pier No.
Pile Dia = __
Pile Dia = __
Pile Dia = __
Pile Dia = __
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
July 2000
9.9-41
BRIDGE DESIGN MANUAL Criteria Substructure Design
Application of LRFD Code to WSDOT Foundation Design
Bearing Capacity, Qult (unfactored)
Uplift Capacity, Qup (unfactored)
Strength and Extreme
Strength and Extreme Event II limit, Dia. = ___ Assumptions: Strength
Dia. = ____ mm Assumptions:
Elevation or Depth
Elevation or Depth
Strength Event II limit, Dia. _____ Dia. = ___ Assumptions: Assumptions:
▲
ExtremeEvent event Extreme I limit (assumes Dia. = ___ for this example
Extreme I limit ExtremeEvent event Dia. = ___ (assumes for this example
that liquefaction Dia. = _____
that liquefaction Dia. = _____
Example Presentation of Pile Bearing Capacity and Uplift Figure 9.9.8-3
P65:DP/BDM9
9.9-42
July 2000
BRIDGE DESIGN MANUAL Criteria Substructure Design 9.99
Bibliography
Bibliography 1.
W. T. Moody, “Moments and Reactions for Rectangular Plates,” U.S. Dept. of the Interior, Bureau of Reclamation, 1970.
2.
Richard Bares, “Tables for the Analysis of Plates, Slabs, and Diaphragms Based on the Elastic Theory,” Wiesbaden, 1971.
3.
Peck, Hansen, Thornburn, “Foundation Engineering,” John Wiley & Sons, Inc., 1967.
4.
Ultimate Strength Design Handbook, Volume 1, ACI Special Publication No. 17, American Concrete Institute, Detroit, 1967.
5.
S. Timoshenko, “Theory of Elastic Stability,” McGraw Hill.
6.
G. A. Leonards, Ed. “Foundation Engineering,” McGraw Hill, 1962. 624.15
7.
W. C. Huntington, “Earth Pressures and Retaining Walls,” Wiley, 1957.
8.
Wayne C. Teng, “Foundation Design,” Prentice-Hall, Inc., 1962.
9.
C. W. Dunham, “The Theory and Practice of Reinforced Concrete,” McGraw Hill, 1953.
L553f
10. Association of Drilled Shaft Contractors, Inc., 6060 N. Central Expressway, Dallas, TX 75206, “Standards and Specifications for the Drilled Shaft Industry,” Revised July 15, 1979. 11. L. C. Reese and S. J. Wright, “Drilled Shaft Manual, Volume I, Construction Procedures and Design for Axial Loading,” U.S. Department of Transportation, Office of Research and Development, Implementation Division, HDV-22, Washington, DC 20590, July 1977. 12. L. C. Reese and J. D. Allen, “Drilled Shaft Manual, Volume II, Structural Analysis and Design for Lateral Loading,” U.S. Department of Transportation, Office of Research and Development, Implementation Division, HDV-22, Washington, DC 20590, July 1977. 13. L. C. Reese, “Analysis of Laterally Loaded Piles, Software Documentation,” Department of Civil Engineering, University of Texas at Austin, Austin, TX 78712, July 1997. 14. Washington State DOT, Olympia, Washington, “Instructions to Engineers Structural Applications Computer Manual.” 15. McDonnell Douglas Automation Company, Box 516, St. Louis, MO 63166, “ICES STRUDL User Manual,” April 19890. 16. Noel J. Everard and Edward Cohen, “Ultimate Strength Design of Reinforced Concrete Columns,” ACI Publication SP-7. 17. R. J. Woodward, W. S. Gardner and D. M. Greer, “Drilled Pier Foundation.” 18. Karl Terzaghi, “Evaluation of Coefficient of Subgrade Reaction,” Geothechnique, Volume V, 1955. 19. Prakash S., “Behavior of Pile Groups Subject to Lateral Loads,” Ph.D. Thesis, University of Illinois, 1962.
9-99:WORK:BDM3
January 1991
9.99 - 1
BRIDGE DESIGN MANUAL Appendix A Substructure Design
Design Aids
24-Inch Diameter Round Column Section Capacity Chart
January 1991
9.2 - A1
BRIDGE DESIGN MANUAL Appendix A Substructure Design
Design Aids
36-Inch Diameter Round Column Section Capacity Chart
9.2 - A2
January 1991
BRIDGE DESIGN MANUAL Appendix A Substructure Design
Design Aids
48-Inch Diameter Round Column Section Capacity Chart
January 1991
9.2 - A3
BRIDGE DESIGN MANUAL Appendix A Substructure Design
Design Aids
60-Inch Diameter Round Column Section Capacity Chart
9.2 - A4
January 1991
BRIDGE DESIGN MANUAL Appendix A Substructure Design
Design Aids
72-Inch Diameter Round Column Section Capacity Chart
January 1991
9.2 - A5
BRIDGE DESIGN MANUAL Appendix A Substructure Design
Design Aids
Column Design Flow Chart
9.2 - A6
January 1991
BRIDGE DESIGN MANUAL Appendix A Substructure Design
Design Aids
Column Design Effective Length Factors
January 1991
9.2 - A7
BRIDGE DESIGN MANUAL Appendix A Substructure Design
Design Aids
Buckling Load — Round Columns
9.2 - A8
January 1991
BRIDGE DESIGN MANUAL Appendix A Substructure Design
Design Aids
Factor Charts
January 1991
9.2 - A9
BRIDGE DESIGN MANUAL Appendix A Substructure Design
Design Aids
Moment Magnification Factor
9.2 - A10
January 1991
BRIDGE DESIGN MANUAL Appendix A Substructure Design
Design Aids
Column Design Example
January 1991
9.2 - A11
BRIDGE DESIGN MANUAL Criteria Simplified Example for Pile Foundation Design, Including Resistance Factor Calibration
Appendix A 1.
Consider the following soil profile for a bridge pier: Factored Load = 900 tons for Strength I Factored Load = 2100 tons for Extreme I
Loose SAND 30 ft
Dense SAND
A pipe pile, closed end, will be used for this example. Assume that the pile supported footing has no bending moments applied to it to keep the example simple. Structural analysis of potential pile options (see AASHTO code for maximum loading allowed for pile stresses and to prevent buckling or crushing) and WSDOT policy indicates that a minimum 18 inch diameter is required for a 300 ton pile and 24 inch diameter is required for a 450 ton pile. Static analysis and previous experience with this bearing stratum indicates that the feasible ultimate pile capacity for the bearing stratum is 300 tons for an 18 inch diameter pipe pile (this is Qult, unfactored). 2.
Using a static analysis method (assume SPT method is used), the unfactored ultimate pile capacity versus depth curve is as follows: Ultimate Pile Capacity (tons) 100
200
300
10 20 Depth (ft) 30 40 50
July 2000
9.9-A-1
BRIDGE DESIGN MANUAL Criteria Simplified Example for Pile Foundation Design, Including Resistance Factor Calibration
Appendix A 3.
The WSDOT driving formula will be used as the quality control method for pile capacity in the field. For this method, φdyn = 0.5 for Strength I (see calibration in Steps 3.a to 3.d below), and φdyn = 1.0 for Extreme I. Pile capacity data which illustrates accuracy of WSDOT formula:
Predicted Ult. Capacity, 2000 Standard Spec. Equ. (kips)
a.
New (1998) Standard Specifications Equation - End of Driving Data - Ultimate Capacity 3500 Rult = FE Ln 10N F = 3.3 (steam) F = 3.1 (OE Diesel) F = 2.4 (CE Diesel)
3000
95% Confidence
2500 Steam Hammers OE Diesel Hammers CE Diesel Hammer
2000 1500
Spe1000
b.
9.9-A-2
500 0 0
500 1000 1500 2000 2500 3000 Load Test Rult - Davisson's Criteria (kips)
3500
Parameters for calibration to determine resistance factor: Parameter
Definition
Value
Bias Factor for Resistance, λR
Ratio of measured to predicted resistance, using log normal mean values
0.97
COVR
Log normal coefficient of variation for resistance prediction
0.356
QD/QL
Dead load to live load ratio
Typical value is 3.0
λQD
Bias factor for structure dead load, using log normal mean values
1.05 (assume CIP concrete structure)
COVQD
Log normal coefficient of variation for structure dead load
0.10 (assume CIP concrete structure)
λQL
Bias factor for structure live load, using log normal mean values
1.15
COVQL
Log normal coefficient of variation for structure live load
0.18
βT
Target reliability index
FS
ASD factor of safety typically used in practice
2 to 2.5 for pile groups 2.5 to 3.0
July 2000
BRIDGE DESIGN MANUAL Criteria Simplified Example for Pile Foundation Design, Including Resistance Factor Calibration
Appendix A c.
Check β implied by current ASD design safety factor:
β=
λ FS QD 2 2 + 1 R QL 1 + COVQD + COVQL ln QD 1 + COVR2 + λ QL λQD DL
[
(
2 2 + COVQL ln (1 + COVR2 ) 1 + COVQD
)]
0.97(2.5)(3.0 + 1) 1 + 0.12 + 0.182 ln 1 + 0.356 2 1.05(3.0) + 1.15 β= = 1.93 ln (1 + 0.356 2 )(1 + 0.12 + 0.182 )
[
]
For FS = 3.0, β = 2.39 (Note: The FS of 3.0 was used when our standard specifications specified the use of the ENR equation, which has a much higher coefficient of variation and tended to over-predict capacity (bias of 0.8, COVR of 0.61, implying a β = 1.11 for FS = 3.0) than our current driving formula. We now use FS = 2.5 with our current driving formula.) In conclusion, a β = 2.0 appears adequate for this analysis considering previous practice. d.
Check φR implied by current ASD safety factor:
γ D QD Q + γ L 1.25 3.0 + 1.75 ( ) L = φR = = 0.55 QD 2 . 5 3 . 0 1 + ( ) FS Q + 1 L For FS = 3.0, φR = 0.46 e.
Calculate the resistance factor, φdyn, for the strength limit state:
φ dyn =
2 2 + COVQL 1 + COVQD QD λR γ D Q + γ L L 1 + COVR2
[
)]
(
λ QD + λ exp β ln 1 + COV 2 1 + COV 2 + COV 2 ( QL R) QD QL QD QL T
γD = LRFD specified load factor for dead load = 1.25 γL = LRFD specified load factor for live load = 1.75
φ dyn
July 2000
1 + 0.12 + 0.182 0.97(1.25(3.0) + 1.75) 1 + 0.356 2 = 0.535 = (1.05(3.0) + 1.15) exp 2.0 ln (1 + 0.3562 )(1 + 0.12 + 0.182 )
[
]
9.9-A-3
BRIDGE DESIGN MANUAL Criteria Appendix A
Simplified Example for Pile Foundation Design, Including Resistance Factor Calibration
If use a βT = 2.5, get φdyn = 0.44. In conclusion, recommend a φdyn = 0.50 for design, based on the use of the WSDOT driving formula. (Note: If use the ENR equation, which has a bias of 0.80 and a coeff. of variation of 0.61, for a βT = 2.0, would need a φR = 0.27. If a CAPWAP is used to determine pile capacity, a bias of 1.45 and a coeff. of variation of 0.44 was obtained for end of driving conditions, resulting in a φR = 0.68 for a βT = 2.0. For a CAPWAP at beginning of redrive conditions, a bias of 1.61 and a coefficient of variation of 0.42 was obtained, resulting in a φR = 0.79 for a βT = 2.0.) 4.
The total factored load for the pier is as shown in the figure in Step 1.
5.
Determine the number of piles to required to support the pier load, using a feasible ultimate pile capacity Qult = 300 tons from Steps 1 and 2. Assume all piles have the same load for this simplified example. (Note that we have not considered a pier loading scenario where the corner piles are more heavily loaded than the interior piles, which would more normally be the case. This simplified uniform loading case was selected to keep this example simple.) For the Strength I limit state:
Factored pier load = 900 tons Resistance/pile = φdynQult = 0.5(300 tons) = 150 tons No. of piles = 900/150 = 6 piles
For the Extreme Event I limit state:
Factored pier load = 2100 tons Resistance/pile = φdynQult =1.0(300 tons) = 300 tons No. of piles = 2100/300 = 7 piles
6.
Determining the estimated pile length from the figure in step 2, Dest. = 50 ft.
7.
For the contract, the pile quantities will be based on an estimated pile length of 50 ft, and the pile capacity shown in the plans will be 300 tons ultimate. The pier will have a seven pile group, because the extreme event limit state controls design in this case.
8.
A pile group settlement analysis was performed with the tips up in the loose sand (depth of 25 ft) and with the pile tips 5 ft into the dense sand (depth of 35 ft). Group settlement in the first case was determined to be 1.5 inches, and in the second case was just below 1 inch. Therefore, minimum pile tips will be specified in the contract, but must check lateral load capacity and deflection, and uplift requirements before selecting a final minimum tip elevation.
9.
The uplift load per pile based on factored loads was determined to be 30 tons from the structural analysis for the strength limit state. For the extreme event limit state, the uplift load per pile was determined to be 100 tons.
10. Calculate the depth required to obtained the required uplift capacity, using static analysis methods. The resistance factor from the AASHTO LRFD design specifications, using the SPT method, φstatic, is 0.35 for the strength limit state and 1.0 for the extreme event limit state.
9.9-A-4
July 2000
BRIDGE DESIGN MANUAL Criteria Simplified Example for Pile Foundation Design, Including Resistance Factor Calibration
Appendix A
Factored Pile Uplift Capacity (tons) 50
100
150
30
10
0.35Qult for strength limit state
20 Depth (ft) 30
1.0Qult for extreme event limit state
40 50
From this figure, the minimum depth required is 31 ft for the strength limit state and 35 ft for the extreme event limit state. 11. Lateral load analysis for deflection and fixity indicates that the pile tips must be at least 27 ft deep. Uplift requirements for the extreme event limit state appears to control the minimum depth required, considering settlement, uplift, and lateral load requirements. Therefore, select a minimum tip elevation based on a minimum pile depth of 35 ft. 12. Based on the pile capacity vs. depth plot and a required minimum penetration of 35 ft, which is less than the estimated tip elevation, overdriving will not be required. Therefore, use a pile capacity of 300 tons ultimate for sizing the pile hammer and pile wall thickness required for constructability.
July 2000
9.9-A-5
BRIDGE DESIGN MANUAL Criteria Detailing Practice
Contents Page
10 10.1 10.1.1
10.1.2 10.1.3 10.1.4 10.1.5
Detailing Practice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Standard Office Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Drawing Orientation and Layout Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Lettering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Line Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. Grpahic Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Structural/Architectural Section, Views, and Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. Revisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Care of Original Manual Drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Final Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bar Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bridge Standard Plans and Office Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plotting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.1-1 1 1 1 1 2 2 5 5 6 6 6 9 11 12 12 12
Appendix A — Design Aids 10.1-A1-1 through 7 Abbreviations 10.1-A2 Structural Steel 10.1-A3 Footing Layout Appendix B — Examples 10.1-B1 Footing Layout
10-CON:V:BDM10
October 1993
10.0 - i
BRIDGE DESIGN MANUAL Criteria Detailing Practice
Drawings
10.0
Detailing Practice
10.1
Drawings The following is to provide the novice with basic information on computer drafting and the fundamentals of file management, and plotting for this activity. Drafting and plotting of drawings is done from BREWS (BRidge Engineers WorkStation) terminals. These terminals operate on the VMS operating system, and GDS is the drafting software used by the Bridge Division. GDS is designed with built-in macros that retrieve information based on filenames that you select from menus or input in batch mode. STDROOT:[FGB]TBFF.FGB is an example of a filename, where: STD:
is the root directory where all the files for the STD job are kept. A job is generally defined as the work to be done for a particular L-XXXX (where L = Location and XXXX = the accounting number assigned to the job)
[FGB]
is the subdirectory where all drawing files are kept.
TBFF
is the user's name for the file. This has a 32 character limit and the first 8 characters must be unique.
.FGB
is the file extension. FBG is always the GDS extension for all drawings.
Please note that all colons, brackets and periods must be used as shown in the example. Directories provide a convenient way to keep job files together, but only if they are used with consistency and updated regularly (clean out obsolete files etc.). Users should choose directory names that are relative to the job they are working on (State Route numbers, bridge numbers, ramp designations, acronyms). This makes it easier for someone to find files that pertain to your job should you be unavailable. Using directories is also important in terms of achieving job files. It is easy to transfer all files that pertain to a job (and only those files that pertain to the job) to a tape when these files are consolidated in one directory. A user can have personal directories or the computer support personnel can set up a job directory to be used by a group of users. To call up a CAD sheet, first select the job directory listing menu in the lower left of the GDS window. A listing of job directories appear on the screen; choose the proper job and then, from the next menu, the CAD sheet file you want.
10.1.1 Standard Office Practices A. Purpose The purpose of these standards is to enable the Bridge Branch to produce consistent and effective plan sheets which will have uniform appearance and information. Engineers and detailers are responsible for ensuring that these criteria are implemented. B. Planning The engineer coordinates with the structural detailer the scope of the detailing work involved. Similar bridge plans and details should be reviewed and kept as examples for maintaining consistent detailing practices. These examples should not be older than three years.
October 1993
10.1 - 1
BRIDGE DESIGN MANUAL Criteria Detailing Practice
Drawings
C. Drawing Orientation and Layout Control 1.
Standard bridge sheet format is 331/2 inches x 221/2 inches with the bottom 2 inches used for title block and related information.
2.
Regular graphite lead or ink shall be used on vellum drawings. Ink or plastic lead only shall be used on mylar drafting film.
3.
Drawings shall be carefully organized so the intent of the drawing can be read easily. North arrows shall be placed on layouts and footing layouts. (See Chapter 2 and 10.1.2 for special requirements for preliminary plan and layout sheets.) Related details shall be grouped together in an orderly arrangemnet. Do not overcrowd the drawing with details. The following is a standard sheet configuration when plan, elevation, and sectional views are required.
PLAN
SECTIONS & DETAILS ELEVATION
D. Lettering 1.
General a.
Text # 4 Ames Lettering Guide Manual, CBR 35 CADD. Titles #6 Ames Lettering Guide Manual, CBR 70 CADD. Underline all titles with a single line having the same weight as the lettering used. Use "bas TITLE".
2.
b.
Lettering shall be upper case only, slanted at approximately 68 degrees angle on the Ames Lettering Guide and of uniform height.
c.
Lettering shall be oriented so as to be read from the bottom right edge of the sheet.
Dimensioning a.
10.1 - 2
A dimension shall be shown once on a drawing, unless repeating it is necessary for clarity. Duplication and unnecessary dimensions should be avoided. All dimension figures shall be placed above the dimension line, and so that they may be read from the bottom of the right edge of the sheet, as shown in the following detail:
October 1993
BRIDGE DESIGN MANUAL Criteria Detailing Practice
October 1993
Drawings
b.
Reinforcing bar clearances need not be specified on plans unless different from the “general Notes.”
c.
When details or structural elements are complex, utilize two drawings. One for dimensions and the other for reinforcing bar details.
d.
Dimensions 12 inches or more shall be given in feet and inches unless the item dimensioned is conventionally designated in inches (for example, 16′ pipe).
e.
In dimensions more than 1 foot, fractions less than 1 inch shall be proceeded by 0 (for example, 3′-03/4″.
f.
Placement of dimensions outside the view, preferably to the right or below, is desirable. However, in the interest of clarity and simplicity it may be necessary to place them otherwise. Examples of dimensioning placement are shown on Figure 10.1.1-1.
10.1 - 3
BRIDGE DESIGN MANUAL Criteria Detailing Practice
Drawings
Figure 10.1.1-1
10.1 - 4
October 1993
BRIDGE DESIGN MANUAL Criteria Detailing Practice
Drawings
E. Line Work 1.
All line work must be of sufficient size, weight, and clarity so that it can be easily read from a print that has been reduced to one-half the size of the original drawing. The line style used for a particular structural outline, centerline, etc., shall be kept consistent wherever that line is shown within a set of bridge plans.
2.
Linework shall have appropriate gradations of width to give line contrast as shown below. Care shall be taken that the thin lines are dense enough to show clearly when reproduced.
3.
When drawing structural sections showing reinforcing steel, the outline of the section shall be a heavier line weight than the rebar. The Mark No. “bubble” for reinforcing steel shall be a rectangle. use “[” “]” to create text rectangles. Epoxy coated reinforcement shall be denoted by a triangle in the following manner.
42
E
#6
F. Scale When selecting a scale, it should be kept in mind that the drawing will be reduced. Generally, the minimum scale for a section detail with rebars is 3/8 inch = 1 foot. The scale used on steel bridge plans will be 3/4 inch = 1 foot minimum.
October 1993
10.1 - 5
BRIDGE DESIGN MANUAL Criteria Detailing Practice
Drawings
Sections and views may be enlarged to show more detail, but the number of different scales used should be kept to a minimum. G. Graphic Symbols 1.
2.
Graphic symbols shall be in accordance with the following: a.
Structural Steel Detailing: AISC Steel Construction Manual see structural steel chart.
b.
Welding symbols: See Lincoln Welding Chart.
Symbols for hatching different material is shown on Figure 10.1.1-2.
H. Structural/Architectural Sections, Views, and Details 1.
A section cuts through the structure; a view is from outside the structure; a detail shows a structural element in more detail — usually a larger scale.
2.
Whenever possible, sections and views shall be taken looking to the right ahead on station or down. Care shall be taken to ensure that the orientation of a detail drawing is identical to that of the plan, elevation, etc., from which it is taken.
3.
On plan and elevation drawings where it is impossible to show cut sections and details, the section and detail drawing should immediately follow the plan and elevation drawing unless there are a series of related plans. If it is impractical to show details on a section drawing, a detail sheet should immediately follow the section drawing. In other words, the order should be from general plan to more minute detail.
4.
Structural and architectural sections, views, and details shall be identified by a circle divided into upper and lower halves. Examples are shown in Figure 10.1.1-3.
I.
5.
Breaks are allowable in lines provided that their intent is clear.
6.
Each pier shall be detailed separately as a general rule. If the intermediate piers are identical except for height, then they can be shown together.
Revisions 1.
10.1 - 6
Manual Techniques a.
Pencil on paper can simply be erased and done over.
b.
Ink on film can be washed off with plain water. Older drawings may need to soak awhile or use rubbing alcohol, but this is preferable to erasing, which will remove the matte finish and make the area difficult to draw on.
c.
Photo lines can usually be eradicated using chemical eradicators (Solutions A and B) available from the vault. This preserves the surface finish. If the chemical is ineffective, check to see if the print is reverse reading in which case the eradicator must be applied to the back. (Reverse reading film positives are actually preferable so that changes are not made on the same surface from which the lines are removed.) Erasing on the front of a mylar sheet should be a last resort as it removes the surface finish.
October 1993
BRIDGE DESIGN MANUAL Criteria Detailing Practice
Drawings
Figure 10.1.1-2
October 1993
10.1 - 7
BRIDGE DESIGN MANUAL Criteria Detailing Practice
Drawings
Figure 10.1.1-3
10.1 - 8
October 1993
BRIDGE DESIGN MANUAL Criteria Detailing Practice
J.
May 1995
Drawings
d.
Plastic lead on film must be erased with a soft eraser, taking care to avoid removing the surface finish.
e.
Film surface damaged by erasing may be restored by careful roughening with a hand eraser.
f.
A chemical solution called sepia eradicator can be used to eradicate lines on sepias. The Bridge Branch seldom uses sepias, but if needed, this solution may be obtained from the stockroom if no one in Bridge has a bottle.
2.
Cadd sheets shall be changed on the cadd film and replotted.
3.
Plan Revisions Versus Addendums a.
All changes to plans require initials of the Bridge Engineer or the Unit Design Supervising Engineer. The locations of all changes (except deletions) shall be shaded so they can be easily found. Shading on preliminary plans is removed before printing the ad copies. The old method of using a number enclosed in a circle enclosed in a triangle is no longer acceptable.
b.
Use the revision block in the left margin to record changes, including the due date and description of each change, made after the preliminary plan is signed by the Bridge Engineer, but before the ad copy. This left margin block is also removed before printing the ad copies.
c.
The Olympia Service Center Plans Branch places a border along the bottom of the plan sheets. This border contains blocks where the Plans Branch assigns sheet numbers, a contract number, a title, and a revision block for the contract plans. For changes made after the ad copy is mailed out (addendum) fill in the revision block, including the due date and description of each addendum. Also, include the contract title, contract number, and sheet number assigned by the Plans Branch (e.g., if bridge sheet number 4 of 7 was assigned plan sheet number 18 or 30 by the Plans Branch, it must remain plan sheet 18 of 30 if revised).
Care of Original Manual Drawings 1.
Original manual drawings should be handled with care to avoid damaging them in any way.
2.
Original manual drawings should be stored flat, either in a designated file or in the drafter’s desk.
3.
If it is necessary to leave an original manual drawing out overnight, it should be covered to reduce exposure to mishap.
4.
An original manual drawing shall not be used for review or checking. All review or checking shall be done from prints.
10.1 - 9
BRIDGE DESIGN MANUAL Criteria Detailing Practice
Drawings
10.1 - 10
May 1995
BRIDGE DESIGN MANUAL Criteria Detailing Practice
Drawings
10.1.2 Final Layout a.
General — The original preliminary plan will be used to create the final layout. Views, data, and notes may be repositioned to improve the final product.
b.
Items on the preliminary plan which should not appear on the final layout are as follows:
c.
1.
Typical roadway sections.
2.
Notes to the district.
3.
Vertical curve, superelevation, and curve data for other than main line.
4.
Other information that was preliminary or that will be found elsewhere in the plans.
Items not normally on the preliminary plan which should be added are as follows: 1.
Test hole locations (designated by 3/16 inch circles, quartered) to plan view.
2.
Elevation view of footings, seals, piles, etc. Show elevation at bottom of footing and, if applicable, the type and size of piling.
3.
General notes above legend in upper right-hand corner usually in place of the typical section.
4.
Title “LAYOUT” in the title block and sheet number in the space provided.
5.
Other features, such as lighting, conduit, signs, excavation, riprap, etc., as determined by the designer.
6.
The layout check list can be used for reference. See Chapter 2.
October 1993
10.1 - 11
BRIDGE DESIGN MANUAL Criteria Detailing Practice
Drawings
10.1.3 Bar Lists Barlist files are different from regular drawing files in that they consist of nine sheets (or windows). In order to view the various sheets type in DR SHEETn where n is a number from 1 to 9. All special bend types must be drawn in the SPECIAL window (DR SPECIAL). If the special bends are drawn in any of Sheets 1 through 9 they will be erased when the BARLIST program is rerun. Special bend types drawn in the SPECIAL window will appear on all sheets and will not be erased when BARLIST is rerun. Barlists have a different set of menus in GDS. While you are in GDS make the following selections: DWG MGT FILES MENU PERS BARLIST This will get you into the special menus to put page numbers on the sheets and plot bar lists. To create page (or plan sheet) numbers for bar list sheets, select the First Sheet No. option in the NAMES menu then enter the value of the first page number. All subsequent sheets will be numbered automatically. If the page number is alphanumeric (that is, it contains both letter and number parts) then choose the Sheet No. Prefix(Letter) option in the NAMES menu. Do not use this option if there is no letter in the page number. There are three ways to plot barlist sheets. Plotting can be done interactively in a GDS session by typing DR SHEETn then using PLOT NOW, or by using the F9 AND F10 function keys (F9 will plot fullsize and F10 halfsize), or by using batch procedures as described in section 10.1.5. The batch routine will ask you how many sheets there are to the barlist and will plot them all whereas PLOTNOW and the function keys will plot only one sheet at a time. Barlist sheets do not require an engineers stamp.
10.1.4 Bridge Standard Plans and Office Standards a.
New standards and revisions to existing Standard Plans are made according to the same standard office practices as plan sheets.
b.
Use of standard sheets for contract plans from the CADD office.
c.
1.
Copy the standard file to your directory and rename the new file by picking “Copy STD file” from the FILES menu.
2.
A plot should be made on which the designer marks the required changes.
3.
Using the marked plot as a guide, the structural detailer makes changes and requests new plots.
4.
SR number, job number, sheet number, and title should be added on layout sheet only.
Changes are made to the master CADD standard file upon the receipt of the revision from the BDM coordinator with his signature/initials and current date of the new revision.
10.1.5 Plotting The user can plot either interactively in GDS or use the SPLOT command after a VMS prompt. Plotting may take as long as 20 minutes, so be patient. It depends on how many plots are already waiting. To see a listing of plot files waiting type PLIST at the VMS prompt. See section 10.1.3 for plotting bar lists.
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October 1993
BRIDGE DESIGN MANUAL Criteria Detailing Practice
Drawings
Interactive Plotting There are two interactive ways to plot in GDS. The user can make menu selections, or can use function keys. PLOT NOW is a menu pick that will plot what is on the screen. Depending on your selection, you can get full size, half size or laser printer plots on the screen. Functions Keys are a short cut method to menu selections. Function key F9 plots a full size sheet and F10 plots halfsize. Batch Plotting Using SPLOT (to Plot a Single Sheet) A drawing may be requested at any terminal by the commands given in the example below. You will need to know the filename, which is shown above the WSDOT logo on every sheet. The procedures would be as shown below for file, NRUP116ROOT:[FGB]LAYOUT.FGB. (beginning at the VMS prompt): VS15A>SPLOT (EXIT or Ctrl/Z to quit) FILENAME: LAYOUT PLOT SIZE: Large OR [Small], or 3 for Laser print: Hit the Return key for the default smal or enter ‘L’ for large. NUMBER OF COPIES [1]: Hit the Return key for the default 1 or enter the number of copies you want. Using MPLOT (to Plot Multiple Sheets) Please note that this routine can tie up a plotter for hours. First, create a data file that includes all the filenames for the sheets you want to plot. In the following example the data file PLOTLIST is set up to plot: NEBAR, JUNKTST, and LAYOUT. The routine begins at the VMS prompt (this is not in the menus). VS15A>MPLOT PLOT LIST INPUT FILE: PLOTLIST DIRECTORY NAME (NO FGB):NRUP116 PLOT SIZE: Large OR [Small]: Hit the Return key for the default small or enter large NOW SUBMITTING PLOT OF NRUP116FGB:NEBAR, TO BATCH Job SINGLE_BATCH_PLOT (queue VS15A_BATCH, entry 20) started on VS15A_BATCH ERROR IN LOCATING NRUP116FGB:JUNKTST.FGB NRUP116FGB:LAYOUT.FGB IS LOCKED BY [RUDEEN] UNABLE TO PLOT As you can see, only one file, NEBAR, was actually plotted. JUNKTST does not exist, and LAYOUT is currently being used by Jeff Rudeen. 10-1:V:BDM10
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BRIDGE DESIGN MANUAL Appendix A Detailing Practice
Design Aids
Abbreviations A. General 1.
Because different words sometimes have identical abbreviations, the word should be spelled out where the meaning may be in doubt.
2.
A few standard signs are in common use in the office of Bridge and Structures. These are listed with the abbreviations.
3.
A period should be placed after all abbreviations, except as listed below.
4.
Apostrophes are usually not used. Exceptions: pav’t., req’d., r’dway.
5.
Abbreviations for plurals are usually the same as the singular. Exceptions: figs., no., ctrs., pp.
6.
Abbreviations in titles should be avoided if possible.
B. List of abbreviations commonly used on bridge plan sheets: A about abutment adjust, adjacent aggregate alternate ahead aluminum Americal Society for Testing and Materials American Association of State Highway and Transportation Officials and angle point approved approximate area asbestos cement pipe asphalt concrete Asphalt concrete pavement asphalt treated base at
abt. abut. adj. agg. alt. ahd. al. ASTM AASHTO
avenue average
& A.P. apprd. approx. A Asb. Cp AC ACP ATB @ (used only to indicate spacing or pricing, otherwise spell out). Ave. avg.
B back back of pavement seat bearing begin horizontal curve (Point of Curvature) begin vertical curve bench mark between bituminous surface treatment bottom boulevard bridge bridge drain
bk. B.P.S. Brg. P.C. BVC BM betw. or btwn. BST bot. Blvd. Br. Br. Dr.
April 1991
10.1 - A1 - 1
BRIDGE DESIGN MANUAL Appendix A Detailing Practice building buried cable C cast-in-place cast iron pipe center, centers centerline center of gravity center to center Celsius (formerly Centrigrade) cement treated base centimeters class clearance, clear compression, compressive column concrete conduit concrete pavement (Portland Cement Concrete Pavement) construction continuous corrugated corrugated metal corrugated steel pipe countersink county creek cross beam crossing cross section cubic feet cubic inch cubic yard culvert D degrees, angular degrees, thermal diagonal(s) diameter diaphragm dimension district double drive E each each face easement East edge of pavement edge of shoulder
10.1 - A1 - 2
Design Aids bldg. BC CIP (C.I.P.) ctr., ctrs. CG ctr. to ctr., c/c C CTB cm. Cl. clr. comp. col. conc. cond. PCCP const. or constr. cont. or contin. corr. CM CSP csk. Co. Cr. X-Bm. Xing X-Sect. CF or cu. ft. or ft.3 cu. in. or in.3 CY or cu. yd. or yd.3 culv. ° or deg. C or F diag. diam. or diaph. dim. Dist. dbl. Dr. ea. E.F. ease., esmt. E. EP ES
April 1991
BRIDGE DESIGN MANUAL Appendix A Detailing Practice endwall electric elevation embankment end horizontal curve (Point of Tangency) end vertical curve Engineer equal(s) estimate(d) excavation excluding expansion existing exterior F Fahrenheit far face far side feet (foot) feet per foot field splice figure, figures flat head foot kips foot pounds footing forward freeway G gallon(s) galvanized galvanized steel pipe gauge General Special Provisions girder ground guard railing H hanger height height (retaining wall) hexagonal high strength high water high water mark highway horizontal hour(s) hundred(s)
April 1991
Design Aids EW elect. el. or elev. emb. P.T. EVC Engr. eq. (as in eq. spaces) or = (mathematical result) est. exc. excl. exp., expan. exist. ext. F FF FS ft. or ’ ft./ft or ’/’ or ’/ft. F.S. fig., figs. F.H. ft-kips ft-lb Ftg. fwd. Fwy. gal. galv. GSP ga. GSP gir. gr. GR hgr. ht. H hex. H.S. H.W. H.W.M. Hwy. horiz. hr. hund.
10.1 - A1 - 3
BRIDGE DESIGN MANUAL Appendix A Detailing Practice I included. including inch(es) inside diameter inside face interior intermediate invert J joint junction K kilometer(s) kilopounds L layout left length of curve linear feet longitudinal lump sum M maintenance malleable manhole manufacturer maximum mean high water mean higher high water mean low water mean lower low water meters mile(s) miles per hour millimeters minimum minute(s) miscellaneous modified monument N National Geodetic Vertical Datum near face near side North Northbound not to scale number; numbers
10.1 - A1 - 4
Design Aids
incl. in. or ” I.D. I.F. int. interm. inv. jt. jct. km. kips, K. LO lt. L.C. L.F. longit. L.S. maint. mall. MH mfr. max. MHW MHHW MLW MLLW m. mi. mph mm. min. min. or ’ misc. mod. Mon. N.G.V.D. NF NS N. NB NTS #, No.; Nos.
April 1991
BRIDGE DESIGN MANUAL Appendix A Detailing Practice O original ground ounce(s) outside diameter outside face out to out overcrossing overhead P page; pages pavement pedestrian per cent pivot point Plans, Specifications and Estimates plate point point of compound curve point of curvature point of intersection point of reverse curve point of tangency point of vertical curve point of horizontal curve point of tangent polyvinyl chloride portland cement concrete pound, pounds pounds per square foot pounds per square inch power pole precast pressure prestressed prestressed concrete pipe Puget Sound Power and Light Q quantity quart R radius railroad railway Range regulator reinforced, reinforcing reinforced concrete reinforced concrete box reinforced concrete pipe required retaining wall
April 1991
Design Aids
O.G. oz. O.D. O.F. O to O O-Xing OH p.; pp. pav’t. Ped. % PP PS&E or PL pt. PCC P.C. P.I. PRC P.T. PVC POC POT PVC PCC lb., lbs., # psf, lbs./ft.2,lbs./ ’,#/ ’ psi, lbs./in.2, lbs./ ”,#/ ” PP P.C. pres. P.S. P.C.P. P.S.P.&L. quant. qt. R. RR Rwy. R. reg. reinf. RC RCB RCP req’d. Ret. Wall
10.1 - A1 - 5
BRIDGE DESIGN MANUAL Appendix A Detailing Practice revised (date) right right of way road roadway route S seconds Section (map location) Section (of drawing) sheet shoulder sidewalk South southbound space(s) splice specification square foot (feet) square inch square yard station standard stiffener stirrup street structure, structural support surface, surfacing symmetrical T tangent telephone temporary test hole thick(ness) thousand thousand feet board measure ton(s) total township transition transportation transverse treatment typical U ultimate undercrossing
10.1 - A1 - 6
Design Aids rev. rt. R/W Rd. rdwy. Rte. sec. or ” Sec. Sect. sht. shldr., shld. or sh. SW, sdwk S. SB spa. spl. spec. sq. ft. or ft.2 sq. in. or in.2 SY, sq. yd. or yd.2 Sta. std. stiff. stirr. St. str. supp. surf. symm. Tan. or T. Tel. temp. T. H. th. M MBM T. tot. T. trans. transp. transv. tr. typ. ult. U-Xing
April 1991
BRIDGE DESIGN MANUAL Appendix A Detailing Practice V variable, varies vertical vertical curve vitrified clay pipe volume W water surface weight(s) welded steel pipe swelded wire fabric West Willamette Meridian wing wall with without Y yard, yards year(s)
Design Aids
var. vert. BV VCP vol. or V W.S. wt. WSP W.W.F. W. W.M. W.W. w/ w/o yd., yds. yr.
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April 1991
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BRIDGE DESIGN MANUAL Appendix A Detailing Practice
Design Aids
Structural Steel Flat pieces of steel are termed plates, bars, sheets, or strips, depending on their dimensions. Bars and plates aregenerally classified as follows: Bars:
up to 6 inches wide, .203 in. (3/16 inch) and over in thickness 6 inches to 8 inches wide, .230 in. (7/32 inch) and over in thickness
Plates:
over 8 inches wide, .230 in. (7/32 inch) and over in thickness over 48 inches wide, .180 in. (11/64 inch) and over in thickness
Thinner pieces up to 12 inches wide are strips and over 12 inches are sheets. A complete table of clasification may be found in the AISC Manual of Steel Construction, 8th Ed. page 6-3. The following table shows the usual method of labeling some of the most frequently used structural steel shapes. Note that the inches symbol (″) is omitted, but the foot symbol (′) is used.
April 1991
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BRIDGE DESIGN MANUAL Appendix A Detailing Practice
Design Aids
Footing Layout The Footing Layout is a plan of the bridge limiting the details shown to those needed to locate the footings. The intent of the footing layout is to minimize the possibility of error at this initial stage of construction. Other related information and/or details such as pile locations, pedestal sizes, and column sizes are considered part of the pier drawing and should not be included in the footing layout. The Footing Layout should be shown on the layout sheet if room allows. It need not be in the same scale. When the general notes and footing layout cannot be included on the first (layout) sheet, the footing layout should then be included on the second sheet. Longitudinally, footings should be located using the survey line to reference such items as the footing, centerline pier, centerline column, or centerline bearing, etc., as shown on the pier details sheet. Appendix 10.5-B1-1 is an example of a footing layout showing: The basic information needed. The method of detailing from the survey line. Notes: 1.
When seals are required, their locations and sizes should be clearly indicated on the footing layout.
2.
This example shows a complicated geometry as the result of the combined efforts of a horizontal curve and the presence of the sharp skew. This is the reason for the odd dimensions shown in factuions of an inch. In most designs the footing layout would be much simpler.
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10.1 - A3
BRIDGE DESIGN MANUAL Criteria Quantities
Contents Page
11.1 11.1.1
General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cost Estimating Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Conceptual Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Preliminary Plan Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Design Stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Final Contract Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.2 Not Included in Bridge Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Computation of Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.1 Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Design Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Bridge Projects Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.2 Procedure for Computation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.3 Data Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.4 Accuracy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Preliminary Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Final Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.5 Excavation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Structure Excavation, Class A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Special Excavation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Shaft Excavation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.6 Shoring or Extra Excavation, Class A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.7 Piling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix A 11.2-A1 Not Included in Bridge Quantities List 11.2-A2 Bridge Quantities Form
11.1-1 1 1 1 1 1 1 11.2-1 1 1 1 1 1 1 1 2 2 2 5 5 5 8
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BRIDGE DESIGN MANUAL Criteria Quantities 11.1
General Considerations
General Considerations The quantities of the various materials involved in the construction of a project are needed for determining the estimated cost of the project and for establishing a base for the contractor’s bid and payment.
11.1.1 Cost Estimating Quantities Quantities for determining cost estimates are often necessary during various stages of project development and required at the completion of the Contract Plans. These quantities are calculated from the best information available at the time (see Chapter 11.2.3). The policy regarding the preparation of quantity calculations is as follows: A. Conceptual Stage During the conceptual stage of a project, estimated quantities may be required to arrive at an estimated cost. The need for quantities will be determined by the Bridge Projects Unit. B. Preliminary Plan Stage Upon completion of the preliminary plan, estimated quantities may be required to arrive at an estimated cost. The need for quantities will be determined by the Bridge Projects Unit. C. Design Stage If requested, quantity calculations shall be made, reviewed, and submitted to the Bridge Projects Unit by the Bridge Design Unit as the design progresses. The first submittal of estimated quantities shall be made as soon as the major dimensions of the structure are determined. As refinements in the design are made, quantities varying more than 10 percent from those previously submitted shall be resubmitted. D. Final Contract Quantities Upon completion of structural design and plans, the quantities of materials involved in the construction of the project shall be computed.
11.1.2 Not Included in Bridge Quantities Items of work which appear in the bridge plan sheets, but for which details, specifications, and quantities are supplied by the district, shall be listed in the “Not Included in Bridge Quantities List” (Form 230-038). This list is required for every bridge, even if no items of work are in the Plans that are in this category. (In this case, fill out the bridge information at the top of the form and write “NONE” across the form.) This form is transmitted to other agencies for further processing. Particular care shall be taken in the preparation of this list as omissions result in inaccurate quantities and frequently necessitate construction change orders.
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11.1-1
BRIDGE DESIGN MANUAL Criteria Quantities 11.2
Computation of Quantities
Computation of Quantities
11.2.1 Responsibilities A. Design Unit The Design Unit is responsible for alerting the Bridge Projects Unit when alterations are made after turn-in to the design features and quantities which will affect the cost of the structure. B. Bridge Projects Unit The Bridge Projects Unit will not be responsible for computing quantities. However, they will be responsible for ensuring that the quantities listed in the Bid Proposal correspond to those received from the Design Unit.
11.2.2 Procedure for Computation Quantities are to be computed and checked independently. The originator and checker shall separately summarize their results on Form 230-031 “Bridge Quantities” in the units shown thereon. The two summaries shall be submitted to the Design Unit Supervisor for comparison. The originator and checker shall use identical breakdowns for each quantity. For example, the originator’s figures for excavation for each of Piers 1, 2, and 3 should be compared separately against the corresponding figures made by the checker. When the desired accuracy is achieved, a Supervisor’s Bridge Quantities form shall be prepared. (This form is the same as previously mentioned except that it is labeled “Supervisor’s Bridge Quantities” and is completed by the supervisor or his designee. If the supervisor elects, the originator’s or the checker’s Bridge Quantities form may be designated as “Supervisor’s Bridge Quantities.”) This form is used by the Bridge Projects Unit to prepare the final bridge cost estimate. All quantity calculations and bridge quantities forms are to be filed in the job file. All subsequent revisions shall be handled in the same manner as the original quantities. On the “Bridge Quantities” form, any revision to the original figure should not be erased but crossed out and replaced by the new figure using a different colored pencil. If there are too many revisions, the old summary sheet should be marked void, left in the file, and a new sheet made out, marked “Revised,” dated, and the original forwarded to the Bridge Projects Unit. Mistakes in quantities can be very costly to the department. The originator and checker must account for all items of work on the “Bridge Quantities” form but must also be careful to enter an item of work only once (e.g., concrete or steel rebar in the superstructure should not be entered both in the lump sum superstructure breakdown and in the unit bid item quantity).
11.2.3 Data Source Quantities of materials for use in preliminary cost estimates can often be obtained from the materials calculated for previous similar designs. This information is available from the Bridge Projcts Unit.
11.2.4 Accuracy A. Preliminary Quantities Quantities used for cost estimates during the conceptual stage of the design are expected to have an accuracy of ±10 percent. The first iteration of quantities, after the preliminary plan has been completed, is expected to have an accuracy of ±5 percent.
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BRIDGE DESIGN MANUAL Criteria Quantities
Computation of Quantities
B. Final Quantities Final quantities to be listed in the Special Provisions and Bid Proposal sheet are to be calculated to have an accuracy of ±1 percent, including bar list.
11.2.5 Excavation A. Structure Excavation, Class A Excavation necessary for the construction of bridge piers and reinforced concrete retaining walls is classified as Structure Excavation, Class A. Payment for such excavation is generally at the unit contract price per cubic yard. The quantity of excavation to be paid for is measured as outlined in Section 209.4 of the Standard Specifications. Computation of the quantity shall follow the same provisions. Designers shall familiarize themselves with this section of the Standard Specifications. Any limits for structure excavation not conforming to the limits specified in the Standard Specifications shall be shown in the Plans. Structure excavation for footings and seals shall be computed using a horizontal limit of 1 foot 0 inches outside and parallel to the neat lines of the footing or seal or as shown in the Plans. The upper limit shall be the ground surface or stream bed as it exists at the time the excavation is started. See Figure 11.2.6-1(A), (B), and (C).
Figure 11.2.6-1
11.2-2
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BRIDGE DESIGN MANUAL Criteria Quantities
Computation of Quantities
Structure excavation for the construction of wing walls shall be computed using limits shown in Figure 11.2.6-2.
Figure 11.2.6-2
Figure 11.2.6-3
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BRIDGE DESIGN MANUAL Criteria Quantities
Computation of Quantities
When bridge approach fills are to be constructed in the same contract as the bridge and the foundation conditions do not require full height fills to be placed prior to the construction of the pier, the approach fill is constructed in two stages, i.e., constructed up to the bottom of footing or 1 foot above the bottom of footing and then completed after the bridge construction. (The Materials Laboratory shall be consulted on the staging method.) The structure excavation shall be computed from the top of the first stage fill. The bottom of a spread footing will be placed 1 foot 0 inches below the top of the first stage fill. See Figure 11.2.6-4(A). The bottom of footings supported on piling will be placed at the top of the first stage fill; therefore, no structure excavation is required (see Figure 11.2.6-4(B)). The limits for stage fills shall be shown in the Plans with the structure excavation, if any.
Figure 11.2.6-4 Prior to pier construction, when (1) a full height fill with or without surcharge is required for settlement, or (2) the original ground line is above the finish grade line, structure excavation shall be computed to 1 foot 0 inches below the finish grade (pavement) line (see Figure 11.2.6-5).
Figure 11.2.6-5
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BRIDGE DESIGN MANUAL Criteria Quantities
Computation of Quantities
B. Special Excavation The excavation necessary for placement of riprap around bridge piers is called Special Excavation (see Figure 11.2.6-6). Special excavation shall be computed from the top of the seal to the existing stream bed or ground line along the slopes indicated in the Plans. Special excavation will only include excavation outside the limits of structure excavation. The limits for special excavation shall be shown in the Plans.
Figure 11.2.6-6 C. Shaft Excavation Excavation necessary for the construction of shaft foundations is generally measured by the cubic yard and paid for at the unit contract price per cubic yard for “Soil Excavation for Shaft Including Haul.” The usual limits for computing shaft excavation shall be the neat lines of the shaft diameter and from the bottom elevation of the shaft as shown in the Plans to the ground surface as it exists at the time of shaft excavation. The methods of measurement and payment and the limits for shaft excavation shall be specified in the Special Provisions.
11.2.6 Shoring or Extra Excavation, Class A All excavation in the dry which requires workmen to enter the excavated area and which has a depth of 4 feet or more is required to be shored, unless the earth face is excavated at its angle of repose (Extra Excavation). All excavation which is 15 feet or less from the edge of a traveled pavement is also required to be shored. All excavation adjacent to railroad tracks shall also be shored. Cofferdams are required for all underwater excavation or excavation affected by ground water. Shoring, cofferdams, or caissons or extra excavation required for the construction of bridge footings and reinforced concrete retaining walls constructed in the wet or dry is classified as Shoring or Extra Excavation, Class A.
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BRIDGE DESIGN MANUAL Criteria Quantities
Computation of Quantities
For the purpose of estimating the cost for cofferdams or for shoring or extra excavation, Class A, it is necessary to compute the peripheral area of an assumed sheet pile enclosure of the excavated area. While payment for Shoring or Extra Excavation, Class A, is made at a lump sum contract price, the costs are a function of overall height of excavation. In general, each side of the excavation for each pier shall be categorized into an average overall height range as shown on Form 230-031 (i.e., less than 6 feet, 6 to 10 feet, 10 to 20 feet, or greater than 20 feet), the area for the side computed using the appropriate width times the average overall height, the overall area for the side shall be entered in the category that matches the side’s average overall height. These calculations are required for each pier of the bridge as applicable. See accompanying Figure 11.2.6-7 and sample calculation. For excavation in the dry, the peripheral area shall be the perimeter of the horizontal limits of structure excavation times the height from the bottom of the footing to the ground surface at the time of excavation. For excavation in water, the peripheral area shall be the perimeter of the horizontal limits of structure excavation times the height from the bottom of the seal to 2 feet above the seal vent elevation. For shaft-type foundations, it is not necessary to compute the area for shoring because the cost for shoring is normally included in the contract price for shaft excavation.
Figure 11.2.6-7
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BRIDGE DESIGN MANUAL Criteria Quantities
Computation of Quantities
Sample Calculation: For this pier (Figure 11.2.6-7): Side A: average height = (4 + 6)/2 = 5 feet width = 15 feet area = 5 × 15 = 75 square feet Side B: average height = (6 + 15)/2 = 10.5 feet width = 20 feet area = 10.5 × 20 = 210 square feet Side C: average height = (10 + 15)/2 = 12.5 feet width = 15 feet area = 12.5 × 15 = 187.5 square feet Side D: average height = (4 + 10)/2 = 7 feet width = 20 feet area = 7 × 20 = 140 square feet For this example height category
area
less than 6 feet
75 square feet
6 feet to 10 feet
140 square feet
10 feet to 20 feet
210 + 188 = 398 square feet
greater than 20 feet
N.A.
These numbers would be entered on Form 230-031 as follows: Std. Item No.
Item Use
Item Description
4012
Std. Item
Shoring or Extra Excavation, Class A Dry:
Quant. (Enter Total for Bridge Here)
Unit of Meas. L.S.
Average Overall Height Pier
6 ft. to 10 ft.
6 ft.
__Example_
_
__________
75
_ S.F.
_
140
10 ft.* to 20 ft.
20 ft.*
_ S.F.
_398(11.5*) S.F.
__ —
_ S.F.
__________ S.F.
__________ S.F.
__________ S.F.
__________ S.F.
__________
__________ S.F.
__________ S.F.
__________ S.F.
__________ S.F.
__________
__________ S.F.
__________ S.F.
__________ S.F.
__________ S.F.
*Indicate Average Height
August 1998
11.2-7
BRIDGE DESIGN MANUAL Criteria Quantities
Computation of Quantities
11.2.7 Piling The piling quantities are to be measured and paid for as outlined in Section 6-05.3(1)D Test Piles, and measurement and payment Sections 605.4 and 6-05.5 of the Standard Specifications. Computation of piling quantities shall follow the same provisions. Designers shall familiarize themselves with these sections of the Standard Specifications. Timber test piles are driven outside the structure limits and are extra or additional piling beyond the required number of production piling. Concrete or steel test piles are driven within the structure limits and take the place of production piling. In this case, the number of production piling is reduced by the number of test piling. The quantity for “Furnishing _____ Piling _____” is the linear feet of production piling below cut-off to the “estimated” pile tip (not “minimum” tip) shown in the soils report. (Does not include test piles.) The quantity for “Driving _____ Piling _____” is the number of production piling driven. (Does not include test piles.) Pile tips are required if so stated in the soils report. The tips on the test piles are incidental to the test pile; therefore, the number of pile tips reported on the Bridge Quantities Form 230-031 should not include the number of pile tips required on the test piles.
DP:BDM11
11.2-8
August 1998
BRIDGE DESIGN MANUAL Appendix A Quantities
Not Included in Bridge Quantities List
Not Included In Bridge Quantities List Environmental And Engineering Service Center Bridge and Structures Office
SR
Job Number
Designed By
Checked By
Project Title Date
Supervisor
Type of Structure
The following is a list of items for which the Bridge and Structures Office is relying on the Region to furnish plans, specifications and estimates. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. DOT
Form 230-038 EF Revised 2/97
11.2-A1 Not Included in Bridge Quantities Form August 1998
11.2-A1
BRIDGE DESIGN MANUAL Appendix A Quantities
Bridge Quantities Form
Bridge Quantities Indicate Unit of Measure: English Metric
Bridge and Structures St. Item No.
Item Use
Item Description
Quantity
0001(E) 0001(M)
Std. Item
Mobilization
0061 0061
GSP Item
Removing Portion of Existing Bridge
Unit of Measure L.S.
Type
L.S. SF/SM
Area
Greater than 12”/305 mm long: Drilled Holes: Less than 12”/305 mm long: Number Diameter Number Diameter Length Inch/mm Inch/mm LF/M Inch/mm
Inch/mm
Inch/mm
Inch/mm
Core Drilled Holes: Less than 12”/305 mm long: Number
0071 0071
GSP Item
Diameter Inch/mm
Sp. Prov.
Std. Item
LF/M LF/M
Inch/mm
Inch/mm
LF/M L.S.
Area
SF/SM L.S.
Area
SF/SM CY/CM
Structure Excavation Class A Incl. Haul Unsuitable: Pier Soil CY/CM CY/CM CY/CM CY/CM Soil
Rock CY/CM CY/CM CY/CM CY/CM
GSP Item
Length
Inch/mm
Removing Temporary Structure
Cofferdam: Pier
4010/8835
Diameter Inch/mm
Inch/mm
Type 4006/8331
Greater than 12”/305 mm long:
Number
Removing Existing Bridge Type
LF/M LF/M
Special Excavation Pier Soil
CY/CM CY/CM CY/CM CY/CM CY/CM
CY/CM CY/CM CY/CM CY/CM
DOT Form 230-031 EF Revised 8/2000
Page 1 of 6
11.2-A2 Bridge Quantities Form August 2000
11.2-A2-1
BRIDGE DESIGN MANUAL Appendix A Quantities
Bridge Quantities Form
St. Item No.
Item Use
Item Description
4013/4013
Std. Item
Shoring or Extra Excavation Class A Dry:
Pier
Quantity
L.S. AVERAGE O VERALL HEIGHT 6 ft./2 m to 10 ft./3 m
20 ft./6 m * SF/SM SF/SM SF/SM SF/SM
AVERAGE O VERALL HEIGHT 20 ft./6 m * SF/SM SF/SM SF/SM SF/SM
AVERAGE HEIGHT
Each
GSP Item
Rock Bolt
---
Sp. Prov.
Soil Excavation For Shaft Including Haul
CY/CM
Sp. Prov.
Rock Excavation For Shaft Including Haul
CY/CM
--
Sp. Prov.
Furnishing and Placing Temp. Casing For
---
Sp. Prov.
Furnishing Permanent Casing For
Sp. Prov.
Placing Permanent Casing For
--
Sp. Prov.
CSL Access Tube
LF/M
4151/8426
Std. Item
St. Reinf. Bar For Shaft
LB/KG
---
Sp. Prov.
Conc. Class 4000P For Shaft
CY/CM
GSP Item
Excavation For Piling
LF/M
4055/8355
Std. Item
Preboring For Pile
LF/M
4060/4060
Std. Item
Furnishing and Driving Concrete Test Pile
Each
4070/8363
Std. Item
Furnishing Concrete Piling -
LF/M
4080/4080
Std. Item
Driving Concrete Pile -
4085/4085
Std. Item
Furnishing and Driving Steel Test Pile
Diam. Shaft Diam. Shaft Diam. Shaft
Diameter Diameter
LF/M LF/M Each
Each Each
4090/8373
Std. Item
Furnishing Steel Piling
LF/M
4095/4095
Std. Item
Driving Steel Pile
Each
4100/4100
Std. Item
Furnishing and Driving Timber Test Pile
Each LF/M
4105/8381
Std. Item
Furnishing Timber Piling - Untreated
4106/8383
Std. Item
Furnishing Timber Piling - Creosote Treated
LF/M
4108/4108
Std. Item
Driving Timber Pile - Untreated
Each
4110/4110
Std. Item
Driving Timber Pile - Creosote Treated
Each
4116/4116
Std. Item
Pile Splice - Timber
Each
--
Sp. Prov.
Pile Tip
Each
DOT Form 230-031 EF
Page 2 of 6
Revised 8/2000
11.2-A2-2
August 2000
BRIDGE DESIGN MANUAL Appendix A Quantities
Bridge Quantities Form
St. Item No.
Item Use
Item Description
Quantity
Unit of Measure
4120/8393
Std. Item
Furnishing Prestressed Hollow Concrete Piling
LF/M
4130/4130
Std. Item
Placing Prestressed Hollow Concrete Pile
Each
4140/4140
Std. Item
Driving Prestressed Hollow Concrete Pile
Each
4145/4145
Sp. Prov.
Pile Loading Test
LF/M
No. of Tests
Each
Pile Size
Ton/Tonne
4147/8410
Std. Item
Epoxy-Coated St. Reinf. Bar For
LB/KG
4147/8410
Std. Item
Epoxy-Coated St. Reinf. Bar For Traffic Barrier
LB/KG
4148/8412
Std. Item
Epoxy-Coated St. Reinf. Bar For Bridge
LB/KG
4149/8420
Std. Item
St. Reinf. Bar For Bridge
LB/KG
4151/8426
Std. Item
St. Reinf. Bar For Traffic Barrier
LB/KG
4151/8426
Std. Item
St. Reinf. Bar For
LB/KG
4165/8428
Std. Item
Wire Mesh
SY/SM
4166/8430
Std. Item
Lean Concrete
CY/CM
--
GSP Item
Conc. Class
CY/CM
4322/8452
Std. Item
Conc. Class 4000/28 for Bridge
CY/CM
4202/8442
Std. Item
Conc. Class 4000/28 for Traffic Barrier
CY/CM
4202/8442
Std. Item
Conc. Class 4000/28 for
CY/CM
4320/8441
Std. Item
Conc. Class 3000/20 for Bridge
CY/CM
4200/8440
Std. Item
Conc. Class 3000/20 for
CY/CM
4325/8477
Std. Item
Conc. Class 5000/35 for Bridge
CY/CM
4205/8475
Std. Item
Conc. Class 5000/35 for
CY/CM
4324/8468
Std. Item
Conc. Class 4000W/28W for Bridge
CY/CM
4204/8466
Std. Item
Conc. Class 4000W/28W for
CY/CM
4183/4183
GSP Item
Conc. Class EA
CY/CM
4185/4185
GSP Item
Conc. Class HE
CY/CM
--
Std. Item
Conc. Class
4184/4184
GSP Item
Cylinder Concrete
LS
CY/CM CY/CM
4188/4188
GSP Item
Fractured Fin Finish
SY/SM
4230/4230
Std. Item
Structural Carbon Steel
LB/KG
4235/4235
Std. Item
Structural Low Alloy Steel
LB/KG
4240/4240
Std. Item
Structural High Strength Steel
LB/KG
4246/4536
Std. Item
Cast Steel
LB/KG
4251/8540
Std. Item
Forged Steel
LB/KG
4256/8546
Std. Item
Cast Iron
LB/KG
4261/8549
Std. Item
Malleable Iron
LB/KG
4267/8552
Std. Item
Ductile Iron
LB/KG
4271/8555
Std. Item
Cast Bronze
LB/KG
DOT Form 230-031 EF Revised 8/2000
August 2000
Page 3 of 6
11.2-A2-3
BRIDGE DESIGN MANUAL Appendix A Quantities
Bridge Quantities Form
St. Item No.
Item Use
Item Description
Quantity
Unit of Measure
4280/8560
Std. Item
Timber and Lumber - Untreated
MBM/M3
4282/8582
Std. Item
Timber and Lumber - Creosote Treated
MBM/M3 MBM/M3
4284/8584
Std. Item
Timber and Lumber - Salts Treated
4300/4300
Std. Item
Superstructure Bridge Plan Area
SF/SM
Roadway Deck Bridge Plan Area
SF/SM
4311/4311
4390/8595
Std. Item
GSP Item
GSP Item
LF/M
LF/M
Electrical Conduit Diameter
4400/8600
LS
Inch
Length
LF/M
Steel Handrail
LF/M LF/M
4405
GSP Item
Bridge Rail - Low Fence Type
4406
GSP Item
Bridge Rail - High Fence Type
LF/M LF/M
4410/8605
GSP Item
Bridge Railing Type
4420
GSP Item
Bridge Grate Inlet
Each
4453/4453
GSP Item
Pigmented Sealer
SY/SM
7169/9572
Sp. Prov.
Structural Earth Wall
SF/SM
---
Sp. Prov.
DOT Form 230-031 EF
Sp. Prov.
Page 4 of 6
Revised 8/2000
11.2-A2-4
August 2000
BRIDGE DESIGN MANUAL Appendix A Quantities
Bridge Quantities Form
Breakdown of Items for Superstructure or Roadway Deck St. Item No.
Item Use
Item Description
Std. Item
Epoxy-Coated Steel Reinforcing Bar
LB/KG
Std. Item
Epoxy-Coated Steel Reinforcing Bar (Traffic Barrier)
LB/KG
--
Std. Item
Steel Reinforcing Bar
LB/KG
--
Std. Item
Steel Reinforcing Bar (Traffic Barrier)
LB/KG
--
GSP Item
Conc. Class
CY/CM
--
Std. Item
Conc. Class 4000D/28D
CY/CM
---
Quantity
Unit of Measure
--
Std. Item
Conc. Class 4000/28
CY/CM
--
Std. Item
Conc. Class 4000/28 (Traffic Barrier)
CY/CM
--
Std. Item
Conc. Class 5000/35
--
Std. Item
Conc. Class
--
GSP Item
Fractured Fin Finish
SY/SM
--
Std. Item
Structural Carbon Steel
LB/KG
--
Std. Item
Structural Low Alloy Steel
LB/KG
--
Std. Item
Structural High Strength Steel
LB/KG LB/KG
CY/CM LS
CY/CM
--
Std. Item
Cast Steel
--
Std. Item
Forged Steel
LB/KG
--
Std. Item
Cast Iron
LB/KG
--
Std. Item
Malleable Iron
LB/KG
--
Std. Item
Ductile Iron
LB/KG
--
Std. Item
Cast Bronze
LB/KG
--
Std. Item
Timber and Lumber - Untreated
MBM/M3
--
Std. Item
Timber and Lumber - Creosote Treated
MBM/M3
--
Std. Item
Timber and Lumber - Salts Treated
MBM/M3
--
Sp. Prov.
Glulam Deck Panels
MBM/M3
--
Std. Item
Electrical Conduit Diameter
LF/M Inch Length
LF/M
---
GSP Item
Steel Handrail
LF/M
GSP Item
Bridge Rail - Low Fence Type
LF/M
--
GSP Item
Bridge Rail - High Fence Type
LF/M
--
Std. Item
Bridge Railing Type
LF/M
--
GSP Item
Traffic Barrier
LF/M
4430/4430
GSP Item
Special Bridge Drain
Each
4433/4433
Sp. Prov.
Modify Bridge Drain
Each
4434/4434
Sp. Prov.
Plugging Existing Bridge Drain
Each
4420/4420
GSP Item
Bridge Grate Inlet
Each
DOT Form 230-031 EF Revised 8/2000
August 2000
Page 5 of 6
11.2-A2-5
BRIDGE DESIGN MANUAL Appendix A Quantities
St. Item No. --
4444/8634
Bridge Quantities Form
Item Use GSP Item
Sp. Prov.
Item Description
Quantity
Expansion Joint System Type
LF/M Length
LF/M
Type
Length
LF/M
Type
Length
LF/M
Expansion Joint Modification Type
Unit of Measure
Length
LF/M LF/M CF/M3
4232/8515
Sp. Prov.
Modified Concrete Overlay
4233/8516
Sp. Prov.
Finishing and Curing Modified Concrete Overlay
SY/SM
4456/8644
Sp. Prov.
Scarifying Concrete Surface
SY/SM
Sp. Prov.
Polymer Concrete Overlay
SY/SM
Sp. Prov.
Further Deck Preparation Volume CF/CM Avg. Depth
Inch/mm
Bridge Deck Repair Volume CF/CM Avg. Depth
Inch/mm
4445/4445
-4455/8643
GSP Item
L.S.
GSP Item
Pigment Sealer
SY/SM
GSP Item
Membrane Waterproofing (Deck Seal)
SY/SM
--
Sp. Prov.
Pot Bearing
Each
--
Sp. Prov.
Disc Bearing
Each
--
Sp. Prov.
Spherical Bearing
Each
--
Sp. Prov.
Cylindrical Bearing
Each
--
Std. Item
Elastomeric Bearing Pad
Each
--
GSP Item
Fabric Pad Bearing
Each
--
Std. Item
Prestressed Conc. Girder Series W42G/W42MG
LF/M
--
Std. Item
Prestressed Conc. Girder Series W50G/W50MG
LF/M
--
Std. Item
Prestressed Conc. Girder Series W58G/W58MG
LF/M
--
Std. Item
Prestressed Conc. Girder Series W74G/W74MG
LF/M
--
Std. Item
Prestressed Conc. Girder Series W83G/W83MG
LF/M
--
Std. Item
Prestressed Conc. Girder Series W95G/W95MG
LF/M
--
Std. Item
Prestressing
LB/KG
--
Sp. Prov.
Precast Prestressed Slab Volume
--
Sp. Prov.
--
Sp. Prov.
Sp. Prov.
--
Sp. Prov.
--
Sp. Prov.
DOT Form 230-031 EF Revised 8/2000
LF/M
CF/CM Length
SF/SM LF/M
Precast Prestressed Double Tee Beam Volume
--
SF/SM
CF/CM Length
Precast Prestressed Tri Beam Volume
11.2-A2-6
L.S.
Precast Segment Volume
CF/CM Length
SF/SM LF/M LF/M
CY/CM
Page 6 of 6
August 2000
BRIDGE DESIGN MANUAL Criteria Construction Costs
Contents Page
12.0 12.1 12.2 12.2.1 12.2.2 12.2.3 12.2.4 12.2.5 12.3 12.3.1
Construction Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Factors Affecting Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Type of Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Location of Project Site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Size of Project Contract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Foundation Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sequencing of Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Development of Cost Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Prospectus and Design Report Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Preliminary Design Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Estimate Updates During Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Contract Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3.2 Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Bridge Projects Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3.3 Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3.4 Cost Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Square Foot Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix A 12.3-A1 Bridge and Structures Estimating Aids 12.3-A2 Substructure Estimating Aids 12.3-A3 Superstructure Estimating Aids 12.3-A4 Miscellaneous Estimating Aids
12.1-1 1 12.2-1 1 1 1 1 1 12.3-1 1 1 1 1 1 1 1 2 2 2 2
P:DP/BDM12
August 1998
12.0-i
BRIDGE DESIGN MANUAL Criteria Construction Costs 12.0
Construction Costs
12.1
Introduction
Introduction
The construction costs itemized in Appendix A are to aid the user in estimating the cost of bridge projects. The costs are based on historical data retrieved from recent WSDOT Contracts. Requests for cost estimates from outside offices should be submitted in writing to the Bridge Projects Unit and a written response will be sent within a reasonable time. Estimates requiring input from the Bridge Design Section will take longer due to project schedule priorities. Telephone requests for cost estimates from outside the Bridge and Structures Office shall be referred to the Bridge Projects Unit. All cost estimates prepared by the Bridge and Structures Office should have the concurrence of the Bridge Projects Engineer.
12-1:P:BDM12
August 1998
12.1-1
BRIDGE DESIGN MANUAL Criteria Construction Costs 12.2
Factors Affecting Costs
Factors Affecting Costs
12.2.1 Type of Structure Many factors, as outlined in Section 2.2.3, must be considered in the selection of the type, size, and location of a bridge or wall. Common structures with normal detail will be on the low end and mid-range of costs. Unique or complex structures will be on the high end.
12.2.2 Location of Project Site Projects in remote areas or with difficult access will generally be on the high end of the cost range, and sometimes beyond.
12.2.3 Size of Project Contract Small projects tend to be on the high end of the cost range while large projects tend to be on the low end of the cost range.
12.2.4 Foundation Requirements Foundation requirements greatly affect costs. Water crossings requiring seals and piles are generally very expensive. Scour requirements can push the costs even higher. The earlier foundation information can be made available the more accurate the cost estimate will be. The Bridge Projects Unit should be made aware of unusual foundation requirements or changes to foundation type as soon as possible for updating of the estimate.
12.2.5 Sequencing of Project Projects with stage construction, detours, temporary construction, etc., will be more expensive.
12-2:P:BDM12
August 1998
12.2-1
BRIDGE DESIGN MANUAL Criteria Construction Costs 12.3
Development of Cost Estimates
Development of Cost Estimates Estimates prepared by the Bridge and Structures Office shall include mobilization but not sales tax, engineering, construction contingencies, or inflation.
12.3.1 Types A. Prospectus and Project Summary Estimates Conceptual cost estimates are prepared when little information about the project is available. Use the construction costs in Appendix A, assuming the worst case conditions, unless actual conditions are known. An example of a worst case condition is pile supported footings. In remote areas, or for small projects, use the high end of the cost range. Use mid-range costs for usual conditions. To cover unforeseen project modifications, add a 20 percent estimate contingency to a prospectus estimate and a 10ˇpercent estimate contingency to a project summary estimate. These contingencies can be adjusted depending on the preliminary information available. B. Preliminary Design Estimates Preliminary design estimates are prepared during the preliminary design stage when the type and size of bridge is known. Limited foundation information is sometimes available at this stage. The construction costs in Appendix A shall be used with an appropriate inflation factor, assuming the worst case conditions, unless foundation conditions are known, along with a minimum of 10 percent contingency to cover scope creep. For bridge rehabilitation projects, add a minimum 20 percent contingency amount to specific items, such as mechancical rehabilitation and structural steel repair, to cover potential increases in costs that often surface after indepth inspections are completed. C. Estimate Updates During Design During the design period, the designer should keep the Bridge Projects Unit informed of significant changes to the design that might affect the cost. Examples of significant changes are: deeper than expected footing and seals, use of piles when none were expected, change of substructure types, and changes to superstructure. This is a critical element in the project budgeting process. D. Contract Estimates The contract estimate is prepared by the Bridge Projects Unit after the Plans and Final Quantities have been submitted to the Bridge Projects Unit for final processing. The contract estimate is prepared using the quantities furnished by the Design Section, unit bid prices from Appendix A, other historical data, and the judgment of the engineer preparing the estimate. Unique, one-of-a-kind projects require special consideration and should include an appropriate construction cost contingency.
12.3.2 Responsibilities A. Bridge Projects Unit The Bridge Projects Unit is responsible for preparing the prospectus, project summary, preliminary, and final contract estimates and updating the preliminary estimate as needed during the design phase of the project. The Bridge Projects Unit assists the regions and outside agencies, such as counties and cities, to prepare conceptual design report and preliminary estimates when requested in writing.
August 1998
12.3-1
BRIDGE DESIGN MANUAL Criteria Construction Costs
Development of Cost Estimates
B. Designer The designer is responsible for providing preliminary quantities and final quantities to the Bridge Projects Unit to aid in the updating of preliminary estimates and the preparation of contract estimates.
12.3.3 Documentation Whenever a cost estimate is prepared by the Bridge and Structures Office for an outside office, a Cost Estimate Summary sheet (Form 230-040) shall be filled out by the engineer preparing the estimate. The Cost Estimate Summary shall be maintained in the Job File. During the design stage, the summary sheet shall be maintained by the Structural Design Unit. It is the design unit supervisor’s responsibility to ensure the summary sheet is up to date when the job file is submitted to the Bridge Projects Unit.
12.3.4 Cost Data A. General The bridge costs summarized in Appendix A represent common highway, railroad, and water crossings. Consult the Bridge Projects Engineer for structures spanning across large rivers or canyons and other structures requiring high clearances or special design and construction features. The square foot costs are useful in the conceptual and preliminary design stages when details or quantities are not available. The various factors affecting costs as outlined in Section 12.2 must be considered in selecting the square foot cost for a particular project. As a general rule, projects including none or few of the high-cost factors will be close to the mid-range of the cost figures. Projects including many of the cost factors will be on the high side. The user must exercise good judgment to determine reasonable costs. During the preliminary stage, it is better to be on the conservative side for budgeting purposes. B. Square Foot Area Compute the square foot area to be used with the square foot cost shall be computed as follows: Bridge Widenings and New Bridges The area of bridges is based on the actual width of the new portion of the roadway slab constructed (measured to the outside edge of the roadway slab) times the length, measured from end of wingwall to end of wingwall, end of curtain wall to end of curtain wall, or back to back of pavement seat if there are no wingwalls or curtain walls. Wingwalls are defined as walls without footings which are cast monolithically with the bridge abutment wall and may extend past the abutment footing. Curtain walls are defined as walls that are cast monolithically with the bridge abutment wall and footing and only extend to the edge of footing. Bridge Rail Replacement The bridge rail and curb removal is based on the total length of the rail and curb removed. Bridge Lengths With Unequal Wingwalls If a bridge has wingwalls or curtain walls of unequal length on opposite sides at a bridge end or wingwalls or curtain walls on one side of a pier only, the length used in computing the square foot area is the average length of the walls. If the wingwalls are not parallel to the centerline of the bridge, the measurement is taken from a projected line from the end of the wingwall normal to the centerline of the roadway.
12.3-2
August 1998
BRIDGE DESIGN MANUAL Criteria Construction Costs
Development of Cost Estimates
Retaining Walls If retaining walls (walls that are not monolithic with the abutment) extend from the end of the bridge, the cost of these walls is computed separately. The area of the wall is based on the height from the top of footing to the top of the wall.
DP:BDM12
August 1998
12.3-3
BRIDGE DESIGN MANUAL Appendix A Construction Costs
Bridge and Structures Estimating Aids BRIDGE AND STRUCTURES (Note: Unit struture costs include mobilization but do not include sales tax, engineering, or contingency) LOW
AVERAGE
HIGH ∆∆
PRESTRESSED CONCRETE GIRDERS SPAN 50-140 FT. Water Crossing w/piling
SF
$ 75.00
$ 90.00
$ 110.00
Water Crossing w/spread footings
SF
70.00
80.00
100.00
Dry Crossing w/piling
SF
75.00
85.00
100.00
Dry Crossing w/spread footings
SF
60.00
70.00
90.00
Water Crossing w/piling
SF
80.00
100.00
130.00
Water Crossing w/spread footings
SF
75.00
95.00
120.00
Dry Crossing w/piling
SF
80.00
100.00
120.00
Dry Crossing w/spread footings
SF
65.00
90.00
110.00
REINFORCED CONCRETE FLAT SLAB SPAN 20-60 FT.
SF
45.00
60.00
80.00
PRESTRESSED CONCRETE SLABS SPAN 13-69 FT.
SF
50.00
70.00
95.00
PRESTRESSED CONCRETE DECKED BULB-TEE GIRDER SPAN 40-115 FT.
SF
80.00
90.00
115.00
STEEL GIRDER — SPAN 60-400 FT.
SF
105.00
125.00
160.00
STEEL TRUSS — SPAN 300-700 FT.
SF
135.00*
STEEL ARCH — SPAN 30-400 FT.
SF
145.00*
CONCRETE BRIDGE REMOVAL
SF
10.00
25.00
40.00
WIDENING EXISTING CONCRETE BRIDGES (Including Removal)
SF
100.00
130.00
185.00
RAILROAD UNDERCROSSING — SINGLE TRACK
LF
RAILROAD UNDERCROSSING — DOUBLE TRACK
LF
REINFORCED CONCRETE AND POST-TENSIONED CONCRETE BOX GIRDER-SPAN 50-200 FT.
July 2000
$7,000.00*(Steel Underdeck Girder) $8,000.00*(Steel Thru-Girder) $11,000.00*
12.3-A1-1
BRIDGE DESIGN MANUAL Appendix A Construction Costs
Bridge and Structures Estimating Aids BRIDGE AND STRUCTURES (Continued) LOW $ 70.00
AVERAGE $ 80.00
HIGH ∆∆
PEDESTRIAN BRIDGE — REINFORCED CONCRETE
SF
$ 90.00
REINFORCED CONCRETE RIGID FRAME (TUNNEL)
SF
REPLACING EXISTING CURBS & BARRIER WITH NEW JERSEY BARRIER (INCLUDING REMOVAL)
LF
100.00
150.00
200.00
REINFORCED CONCRETE RETAINING WALL (EXPOSED AREA)
SF
35.00
50.00
65.00
SOLDIER PILE TIEBACK WALL (EXPOSED AREA)
SF
100.00
120.00
150.00
80.00*
MSE WALL PRECAST CONCRETE PANELS
SF
13
24
35
MSE WALL WELDED WIRE
SF
11
18
25
MSE WALL CIP CONCRETE FACE
SF
30
35
40
SOIL NAIL WALL
SF
20
30
40
CONCRETE FACING PERMANENT GEOSYNTHETIC WALL
SF
11
15
30
CONCRETE CRIB WALL CONCRETE HEADERS
SF
20
30
40
*Based on limited cost data. Check with the Bridge Support Engineer. Bridge areas are computed as follows: Typical Bridges: Width x Length Width: Total width of deck, including portion under the barrier. Length: Distance between back of pavement seats, or for a bridge having wingwalls, 3″-0″ behind the top of the embankment slope; typically end of wingwall to end of wingwall, reference Standard Plans H9. Special Cases: Widenings — Actual area of new construction. Tunnel — Outside dimension from top of footing to top of footing over the tunnel roof, i.e., including walls and top width. ∆∆ For small jobs (less than $100,000), use the high end of the cost range as a starting point. P65:DP/BDM12
12.3-A1-2
July 2000
BRIDGE DESIGN MANUAL Appendix A Construction Costs
Substructure Estimating Aids SUBSTRUCTURE
BID ITEMS
COST/UNIT ∆∆
UNIT
Structure Excavation Class A Incl. Haul Earth Rock Inside Cofferdam — Earth — Rock
Cu. Yd. Cu. Yd. Cu. Yd. Cu. Yd.
Shoring Extra Excavation Class A Dry — Depth under 6′ Dry — 6′ - 10′ Dry — 10′ - 20′
$
10.00 100.00 20.00 100.00
— — — —
$
25.00 200.00 30.00 175.00
Sq. Ft. Sq. Ft. Sq. Ft.
2.00 6.00 10.00
— — —
6.00 10.00 20.00
Cofferdam
Sq. Ft.
20.00
—
30.00
Preboring For Standard Piles
Lin. Ft.
25.00
—
45.00
3,000.00 3,000.00 1,500.00
— — —
5,000.00 4,000.00 2,500.00
30.00 25.00 8.00 7.00
— — — —
40.00 30.00 10.00 9.00
Furnishing & Driving Test Piles Concrete Steel Timber
Each Each Each
Furnishing Piling Conc. _____ Diam. Steel — TYP HP 12x53 Timber — Creosote Treated Timber — Untreated
Lin. Ft. Lin. Ft. Lin. Ft. Lin. Ft.
Pile Tip CIP Concrete (Steel Casing — Short Tip) CIP Concrete (Steel Casing — 10 Stinger) Steel (H-Pile) Timber (Arrow Tip)
Each Each Each Each
150.00 4,000.00 100.00 20.00
— — — —
200.00 5,000.00 200.00 40.00
Driving Piles (40′ - 70′ Lengths) Concrete _____ Diam. Steel Timber
Each Each Each
400.00 300.00 200.00
— — —
800.00 700.00 400.00
Cu. Yd. Cu. Yd.
200.00 350.00
450.00 650.00
Lin. Ft.
100.00
300.00
Lin. Ft. Each Est. Cu. Yd.
100.00 1,000.00 10,000.00 125.00
600.00 1,500.00 25,000.00 200.00
Shafts Soil Excavtion For Shaft Including Haul Rock Excavation For Shaft Including Haul Furnishing and Placing Temp. Casing For Shaft Furnishing Permanent Steel Casing For Shaft Placing Permanent Steel Casing For Shaft Shoring or Extra Excavation cl. A — Shaft Conc. Class 4000P For Shaft
July 2000
12.3-A2-1
BRIDGE DESIGN MANUAL Appendix A Construction Costs St. Reinf. Bar For Shaft CSL Access Tubes Force Account Remvoing Obstrucitons For Shaft
Substructure Estimating Aids Lb. Lin. Ft.
40.00 1.50
50.00 3.50
Est.
10% of all of above shaft ______
St. Reinf. Bar For Bridge
Lbs.
0.45
—
0.60
Epoxy-Coated St. Reinf. Bar For Bridge
Lbs.
0.60
—
0.80
Conc. Class 4000W
Cu. Yd.
100.00
—
150.00
Conc. Class 4000P
Cu. Yd.
100.00
—
150.00
Conc. Class 4000 (Footings)
Cu. Yd.
300.00
—
400.00
Conc. Class 4000 (Abut. & Ret. Walls)
Cu. Yd.
300.00
—
400.00
Conc. Class 5000
Cu. Yd.
350.00
—
450.00
Lean Concrete
Cu. Yd.
100.00
—
130.00
Concrete Class 4000 P (CIP Piling)
Cu. Yd.
100.00
—
175.00
P65:DP/BDM12
12.3-A2-2
July 2000
BRIDGE DESIGN MANUAL Appendix A Construction Costs
Superstructure Estimating Aids SUPERSTRUCTURE
BID ITEMS Elastomeric Bearing Pads Girder Seat Girder Stop
COST/UNIT ∆∆
UNIT Each Each
Spherical and Disc, Bearings (In place with plates)
Kip
Fabric Pad Bearing (In place, including all plates, TFE, etc.)
Each
$
80.00 50.00
— —
$ 100.00 70.00
7.00
—
10.00
1,000.00
—
2,000.00
Prestressed Concrete Girder W42G (Series 6) W50G (Series 8) W58G (Series 10) W74G (Series 14) W83G W95G
Lin. Ft. Lin. Ft. Lin. Ft. Lin. Ft. Lin. Ft. Lin. Ft.
Structural Carbon Steel (Steel girder, etc. when large amount of steel is involved)
Lbs.
0.80
—
1.35
Structural Low Alloy Steel (Steel girder, etc. when large amount of steel is involved)
Lbs.
1.00
—
1.40
Structural Steel (Sign supports, etc. when small amounts of steel are involved)
Lbs.
2.00
—
4.00
Timber & Lumber Creosote Treated Salts Treated Untreated Lagging (in place) Untreated Lagging (in place) Creosote Treated
MBM MBM MBM MBM MBM
1,500.00 1,800.00 1,000.00 1,400.00 1,900.00
— — — — —
2,000.00 2,500.00 1,500.00 1,800.00 2,500.00
Expansion Joint Modification
Lin. Ft.
250.00
—
350.00
Expansion Joint System Compression Seal Modular (Approx. $100 per inch of movement) Strip Seal
Lin. Ft. Lin. Ft. Lin. Ft.
20.00 500.00 100.00
— — —
50.00 2,000.00 200.00
Bridge Drains
Each
250.00
—
500.00
Bridge Grate Inlets
Each
1,200.00
—
1,500.00
Conc. Class 5000
Cu. Yd.
500.00
—
600.00
Con. Class 5000 (Segmental Constr.)
Cu. Yd.
600.00
—
700.00
Con. Class 4000D (Deck Only)
Cu. Yd.
450.00
Conc. Class 4000
Cu. Yd.
400.00
July 2000
85.00 90.00 100.00 110.00 130.00 140.00
550.00 —
500.00
12.3-A3-1
BRIDGE DESIGN MANUAL Appendix A Construction Costs
Superstructure Estimating Aids SUPERSTRUCTURE (Continued)
BID ITEMS
COST/UNIT ∆∆
UNIT
Concrete Class EA (Exposed Aggregate)
Cu. Yd.
350.00
—
500.00
Concrete Class 4000 LS (Low Shrinkage)
Cu. Yd.
$300.00
—
$400.00
Concrete Class 5000 LS
Cu. Yd.
400.00
—
500.00
St. Reinf. Bar
Lb.
0.40
—
0.55
Epoxy-Coated Steel Reinforcing Bar
Lb.
0.50
—
0.75
Post-tensioning Prestressing Steel (Includes Anchorages)
Lbs.
1.50
—
2.50
Traffic Barrier
Lin. Ft.
55.00
—
75.00
Metal Railing (Type BP & BP-B)
Lin. Ft.
35.00
—
55.00
Metal Railing (Thrie Beam)
Lin. Ft.
40.00
—
65.00
Modified Conc. Overlay
C.F.
25.00
—
60.00
Furnishing and Curing Modified Conc. Overlay
Sq. Yd.
40.00
—
70.00
Scarifying Conc. Overlay
Sq. Yd.
8.00
—
12.00
Polymer Concrete
Sq. Yd.
45.00
—
100.00
P65:DP/BDM12
12.3-A3-2
July 2000
BRIDGE DESIGN MANUAL Appendix A Construction Costs
Miscellaneous Estimating Aids Miscellaneous
BID ITEMS
COST/UNIT ∆∆
UNIT
Electrical Conduit, metal 2≤
Lin. Ft.
Sign Support (Brackets, Mono, or Truss Sign Bridges)
Lbs.
Concrete Surface Finishes Fractured Fin Finish Exposed Aggregate Finish* Pigmented Sealer
Sq. Yd. Sq. Yd. Sq. Yd.
$ 8.00
—
$ 15.00
2.00
—
4.00
17.00 17.00 5.00
— — —
28.00 22.00 8.00
500.00
—
700.00
.08
—
.10
ˇ *Requires the use of concrete Class EA Painting Existing Steel Bridges (Lead Base)
Ton. (Steel)
Painting New Steel Bridges
Lb. (Steel)
Mobilization
Sum of Items
Masonry Drilling ∆ Holes up to 1 foot deep 1″ diameter 1 12 ″ 2″ 2 12 ″ 3″ 3 12 ″ 4″ 5″ 6″ 7″
24.00 25.00 28.00 30.00 32.50 42.50 47.50 53.00 60.00 77.00
10%
∆ For holes greater than 1-foot deep up to 20 feet deep, use 1.5 × above prices. If drilling through steel reinforcing, add $16.00 per lineal inch of steel drilled. Removal of Rails and Curbs
Lin. Ft.
$ 80.00
—
$130.00
Removal of Rails, Curbs, and Slab
Sq. Ft.
25.00
—
50.00
Further Deck Preparation
Cu. Ft.
100.00
—
150.00
Bridge Deck Repair
Cu. Ft.
110.00
—
160.00
Removing ACP from bridge deck
Sq. Yd.
6.00
—
10.00
P65:DP/BDM12
July 2000
12.3-A4
BRIDGE DESIGN MANUAL Criteria Construction Specifications and Estimates
Contents Page
13.0 13.1
Construction Specifications and Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Standard Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Amendments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Special Provisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Addendum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. AD Copy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.3 Reviewing a Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Job File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Bridge Rating Form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. PS&E Check List (Form 230-037) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D. Summary of Quantities (Form 230-031) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Not Included in Bridge Quantities (Form 230-038) (see example 13.0 B-3) . . . . . . . . . . . . . . G. Foundation Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.4 Preparing the Cost Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.5 Preparing the Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.6 Preparing the Working Day Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.7 Reviewing Projects Prepared by Consultants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.8 Submitting the PS&E Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.9 Office Copy Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix A — Design Aids and Forms 13.6-A1 Construction Time Rates Appendix B — Design Examples 13.0-B1 Construction Working Day Schedule 13.0-B2 Cost Estimate Summary 13.0-B3 Project Cost vs. Time Chart
1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 3 3 3 3 3 3 4 4 4 4 4 4 5 5 5
P:DP/BDM13
August 1998
13.0-i
BRIDGE DESIGN MANUAL Criteria Construction Specifications and Estimates 13.0
Construction Specifications and Estimates
13.1
General Introduction The Bridge Projects Unit prepares the specifications and estimates (S&E) for all structural projects designed or reviewed by the Bridge and Structures Office. The preparation includes reviewing the job file, plans, PS&E check list, “Not Included in Bridge Quantities List,” foundation report, and preparing the cost estimates, specifications, and working day schedules; and submitting the PS&E package to the Region or Plans Branch. For projects designed by a Bridge Design Unit, the Bridge Projects Unit normally has three weeks to prepare the S&E package and submit it to the Bridge and Structures Engineer and another week to submit it to the Region or Plans Branch. For projects designed by a consultant, the Bridge Projects Unit normally has three weeks to review and comment on the 90 percent design package. After the consultant submits the 100 percent design package, the Bridge Projects Unit has three weeks to prepare the S&E package and submit it to the Bridge and Structures Engineer and another week to submit it to the Region or Plans Branch.
13.2
Definitions A. Standard Specifications Standard Specifications for Road, Bridge, and Municipal Construction, provisions and requirements for the prescribed work. B. Amendments Approved revisions or supplements to specific sections of the standard specifications. C. Special Provisions Supplemental specifications and modifications to the standard specifications and the amendments to the standard specifications that apply to an individual project. D. Addendum A written or graphic document issued to all bidders and identified as an addendum prior to bid opening, which modifies or supplements the bid documents and becomes a part of the contract. E. AD Copy The AD copy is the contract document advertised to prospective bidders. F. The governing order is as follows: Special Provisions, Contract Plans, then Standard Specifications for Road, Bridge, and Municipal Construction.
13.3
Reviewing a Project A. Job File Check for the items of work that need to be included in the PS&E; items that need special provisions or cost estimates; and items that require additional research and information. Check that the job file fly leaf information has been completed by the designer (Form 221-076).
August 1998
13-1
BRIDGE DESIGN MANUAL Criteria Construction Specifications and Estimates B. Bridge Rating Form Bridge rating forms are prepared by the designer and submitted as part of the design package to the Bridge Projects Unit which are then forwarded to the Bridge Preservation Unit. C. PS&E Check List (Form 230-037) Check for special materials, construction requirements, permits, etc., that may need Special Provisions such as: • Permits:
United States Coast Guard
• Agreements:
utilities on bridge, etc.
• Materials:
structural steel, etc.
• Construction Requirements:
temporary access, stage construction, or construction over railroad
• Special Items:
modified concrete overlay or architectural treatment
D. Summary of Quantities (Form 230-031) Verify that the Summary of Quantities is labeled as “Supervisor’s Bridge Quantities.” That is, the supervisor shall summarize the quantities and resolve all discrepencies between the designer and checker. E. Plans Check the plans for materials, special items, stage construction, standard notes and consistent terminology, etc. F. Not Included in Bridge Quantities (Form 230-038) (see example 13.0 B-3) Check for items shown on the plans that will be included in region’s PS&E work such as items outside the structure limits. These shall be listed on the Not Included in Bridge Quantities List. For example: temporary traffic barrier, gravel backfill for walls, etc. G. Foundation Report Check that recommended foundation types and elevations are shown on the plans. Obtain a copy of the final Foundation Report for the S&E file. Check for settlement period of embankment, special excavation, etc., that need special provisions and/or cost estimates. Check for the number of test holes and the locations listed on the layout sheet against the final Foundation Report.
13.4
Preparing the Cost Estimates A. General Preparing the Bridge Cost Estimate consists of listing the standard and nonstandard bid items. The software Excel is used to prepare the Cost Estimate. The Bridge Projects Unit uses a standard output format for Cost Estimates. This output includes the tabulation of all items, a breakdown for each lump sum item, and square foot cost of the structure. B. Procedure Pricing for the bid items above can be based on the Construction Cost Estimating Aids listed in Appendix A of Chapter 12, bid tabulations from previous contracts, and the Unit Bid Average listing from the Plan Branch Office. The engineer needs to make adjustments for inflation, site location, quantities involved, total of the work involved, etc.
13-2
August 1998
BRIDGE DESIGN MANUAL Criteria Construction Specifications and Estimates Each standard item has a corresponding code number. Both the item and code number are stored on the Excel worksheet. The nonstandard unit contract items do not have standard item numbers for coding. All estimates shall include mobilization, but do not include sales tax, engineering, or contingencies.
13.5
Preparing the Specifications A. General There are three types of specifications: (1) Standard Specifications and Amendments to the Standard Specifications, (2) General Special Provisions (GSP), and (3) Bridge Special Provisions (BSP). All of the Amendments, GSP’s, and BSP’s texts are stored in the computer system and can be retrieved from the Plans Branch Text Processing. The texts are divided into topic documents. Each document is named under a coded name list under the Amendments, GSP, or BSP indexes. If any modifications are made to a GSP, then the date must be dropped and the document code must be changed. B. Procedure In preparation of the bridge specifications, all of the applicable documents of the Amendments, GSPs, and BSPs are each listed in numerical order, and required fill-ins are provided, then these are submitted to text processing. The Plans Branch Text Processing will process the requested list using standard Form 220-013A (Appendix 13.5-A1.) For special provisions not covered by a GSP or BSP, appropriate documents must be written in the standard format including description, materials, construction requirements, measurement, and payment. These documents are coded and placed on the appropriate order of the listing and are sent to the Plans Branch Text Processing for text processing. The completed text of the bridge specifications shall be checked for typing errors, contents of the texts, consistent terminology for materials called for in the plans, and pay items called for in the estimates. They shall be revised and reviewed as necessary before the final office copy is printed for the S&E package.
13.6
Preparing the Working Day Schedule A. General The Bridge Projects Unit calculates the number of the working days necessary to construct the bridge portion of the contract, and enters the time in the special provision “Time for Completion.” The working days are defined in the Section 1-08.5 of the Standard Specifications. B. Procedure The first task of estimating the number of working days is to list all the construction activities involved in the project. These include all actual construction activities such as excavation, forming, concrete placement, and curing; and the nonconstruction activities such as mobilization, material and shop plan approval. Special conditions such as staging, limited access near wetlands, limited construction windows for work in rivers and streams, limited working hours due to traffic and noise restrictions, require additional time.
August 1998
13-3
BRIDGE DESIGN MANUAL Criteria Construction Specifications and Estimates The second task is to assign the number of working days to each construction activity above (see Appendix 13.6-A1). “Construction Time Rate” can be used as a guide to estimate construction time required. This table shows the average rate of output for a single shift, work day only. Adjustment to the rates of this table should be made based on the project size, type of work involved, location of the project, etc. In general, larger project will have higher production rates than smaller projects, new construction will have higher production rates than widening, and unstaged work will have higher production rates than staged work. The last step is to arrange construction activities, with corresponding working days, into a construction schedule on a bar chart, either by hand on the Construction Working Day Schedule Form 230-041 (see Appendix 13.0 B7) or by computer on the Microsoft Project Program. List the activities in a logical construction sequence, starting from the substructure to the superstructure. Items shall overlap where practical and the critical path shall be identified.
13.7
Reviewing Projects Prepared by Consultants A. General Consultants are required to submit the 90 percent complete design package to the Bridge and Structures Office for review and comment three weeks prior to submiting the 100 percent complete design package. The package shall be in the same format as those prepared by the Bridge and Structures Office. B. Procedure The Bridge Projects Unit reviews and comments on the 90 percent complete design package. After the consultant makes corrections and resubmits the package as 100 percent complete, the Bridge Projects Unit prepares and forwards the PS&E package to the Plans Branch.
13.8
Submitting the PS&E Package A. General The PS&E package includes: 1.
Cover letter to the Bridge and Structures Engineer
2.
Cover letter to the Region or Plans Branch. For Region Ad and Award projects, the paragraph regarding “As Constructed Plans” and the cc: to “Construction Support Unit Technician” are only used when work related to a bridge is part of the project, not for retaining walls, signs, etc. away from a bridge.
13-4
3.
Bridge Construction Cost Estimate
4.
Not Included in Bridge Quantity List
5.
Special Provisions
6.
Log of Test Borings
7.
One Reduced Xerox Set of Plans
8.
Cost Estimate Summary (see Appendix 13.0-B2)
9.
Construction Working Day Schedule
August 1998
BRIDGE DESIGN MANUAL Criteria Construction Specifications and Estimates B. Procedure Check with a resident specification and estimate engineer for the latest and most current acceptable distribution list for the region in question.
13.9
Office Copy Review A. Description The Office Copy Review is a set of plans and special provisions to be reviewed before the AD Copy is printed. Normally, the Office Copy is received for reviewing two weeks prior to the AD date. B. Procedure The review of the Office Copy is to make sure the Bridge PS&E and Log of Test Boring have been properly incorporated before the printing of the AD Copy; and to check the coordination between the region’s plans and Bridge Office’s plans. Revisions, changes, additions, deletions shall be submitted to the regions or the Plans Branch by the Specifications and Estimate Engineer.
P:DP/BDM13
August 1998
13-5
BRIDGE DESIGN MANUAL Appendix A Construction Specifications and Estimates
Construction Time Rates
Construction Time Rates Operation Substructure Structure Exc. & Shoring *Seals *Footings *Abutment Walls *Wingwalls *Retaining Walls with Footings *Columns Falsework for X-beams *X-beams Driving Test Piles Furnishing Piles Precast Concrete Cast-in-Place Concrete Steel Timber Driving Piles Concrete Steel Timber Prestressed Girders Girder Fabrication Set Girders *Slab & Diaphragms Box Girders Span Falsework *Bottom Slab *Webs, Diaphragms, and X-beams *Top Slab Stress and Grout Strands Strip Falsework T-Beam Span Falsework *Girders, Diaphragms, and Slab Strip Falsework Flat Slab Span Falsework *Slab and X-beams Strip Falsework Steel Girder Girder Fabrication Girder Erection *Slab Painting Miscellaneous *Traffic Barrier *Traffic Railing & Sidewalk *Concrete Overlay Expansion Joint Replacement
Units**
Minimum Output
Maximum Output
Average Output
C.Y./Day C.Y./Day C.Y./Day C.Y./Day C.Y./Day C.Y./Day C.Y./Day C.Y./Day C.Y./Day Each/Day
20 10 6 4 1 4 3 13 16 1
150 20 14 19 2 17 8 4 20 2
Days Days Days Days
40 15 30 20
20 2 2 2
30 5 10 5
L.F./Day L.F./Day L.F./Day
100 100 100
200 200 200
150 150 150
Days L.F./Day C.Y./Day
70 200 6
35 1,450 18
45 550 11
S.F./Day C.Y./Day C.Y./Day C.Y./Day LBS/Day S.F./Day
150 3 5 7 4,500 1,500
900 11 25 12 8,000 3,000
700 8 18 9 6,000 2,200
S.F./Day C.Y./Day S.F./Day
500 6 1,000
1,000 15 2,000
700 10 1,500
S.F./Day C.Y./Day S.F./Day
100 6 300
600 15 1,000
250 10 500
Days L.F./Day C.Y./Day S.F./Day
200 50 6 1,000
110 200 15 3,000
150 100 10 2,000
L.F./Day L.F./Day S.Y./Day Days/Lane Closure
20 15 200 4
80 60 300 6
40 35 250 8
80 15 10 7 1.5 11 4 10 18 1
* Concrete ** All times are based on 8-hour work days 13-6A:P:BDM13
August 1998
13.6-A1
BRIDGE DESIGN MANUAL Appendix B Construction Specifications and Estimates
Cost Estimate Summary
P:DP/BDM13
August 1998
13.0-B2
BRIDGE DESIGN MANUAL Appendix B Construction Specifications
Project Cost vs. Time Chart
P:DP/BDM13
August 1998
13.0-B3
BRIDGE DESIGN MANUAL Criteria Bridge Rating
Contents Page
14.0 14.1 14.1.1 14.1.1.1 14.1.1.2 14.1.2 14.1.2.1 14.1.2.2 14.1.3 14.1.4 14.1.4.1 14.1.4.2 14.1.5 14.1.6 14.1.6.1 14.1.6.2 14.1.7 14.1.8 14.2 14.2.1 14.2.1.1 14.2.1.2 14.2.2 14.2.2.1 14.2.2.2 14.2.2.3 14.2.3 14.2.4 14.2.5 14.2.6 14.2.6.1 14.2.6.2 14.2.7 14.2.8 14.2.9 14.3 14.4 14.99
Bridge Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rating Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Resistance Factor Rating (LRFR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Factor Design Rating (LFDR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Live Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Resistance Factor Rating (LRFR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Factor Design Rating (LFDR) for National Bridge Inventory (NBI) . . . . . . . . . . . . . . . . . Dead Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Resistance Factor Rating (LRFR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Factor Design Rating (LFDR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Capacity Reduction Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Resistance Factor Rating (LRFR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Factor Rating (LFDR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reduction Factors (for both LRFR and LFDR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ratings for Overloads (LRFR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Special Rating Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prestressed Concrete Bridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Resistance Factor Rating (LRFR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Factor Design (LFD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reinforced Concrete Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Decks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Crossbeams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . In-Span Hinges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Box Girder Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete T-Beam Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Concrete Flat Slab Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steel Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steel Floor Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Steel Truss Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Timber Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Widened or Rehabilitated Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Other Special Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Rating Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Load Rating Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
August 1998
14.1-1 1 1 2 3 3 3 3 4 4 4 7 7 7 7 8 8 8 14.2-1 1 1 1 2 2 3 3 3 3 3 3 4 4 4 4 5 14.3-1 14.4-1 1
14.0-i
BRIDGE DESIGN MANUAL Criteria Bridge Rating
Contents
Appendix A — Design Aids 14.0-A1 Load Rating Flow Chart 14.0-A2 Source of Rating Factors 14.0-A3 Bridge Inspection Report Condition Codes 14.0-A4 Span Type Abbreviations 14.0-A5 Bridge Rating Summary 14.0-A6 Load Rating Flow Chart 14.0-A7 3D Live Load Modeling Guidelines for Truss Bridges
P:DP/BDM14 9807-0802
14.0-ii
August 1998
BRIDGE DESIGN MANUAL Criteria Bridge Rating 14.0
Bridge Rating
14.1
General
General
Bridge Rating is a procedure to evaluate the adequacy of various structural components to carry predetermined applied loads. The WSDOT Bridge Preservation Section is responsible for the bridge inventory and load rating of existing and new bridges in accordance with the NBIS and the AASHTO Manual for Condition Evaluation of Bridges, latest edition. As presently required, only elements of the superstructure will be rated. Generally, superstructure shall be defined as all structural elements above the column tops including drop cross-beams. Load rating shall be part of structural design for all, widened (one lane width or more throughout the length of the bridge), or rehabilitated bridges where the rehabilitation alters the load carrying capacity of the structure. The carrying capacity of a widened or rehabilitated structure shall equal or exceed the capacity of the existing structure. The Bridge Design Section generally will not be required to load rate new bridges/designs. However, for the more complex structures where computer models are used in the design/analysis, a copy of the computer models shall be made and submitted to the Bridge Load Rating Engineer in the Bridge Preservation Section. In order to provide a baseline rating for new bridges, the bridge designer shall make rating calculations and complete a Bridge Rating Summary (see Appendix 14.0-A5) as part of the design process. The designer shall place the original rating calculations and report and a copy of the bridge plans in an Accopress-type binder (see Section 14.4). When the bridge design is complete, the designer shall forward the completed bridge rating package to the Bridge Projects Unit, then the Bridge Projects Unit will forward the rating package to the Bridge Preservation Section. The bridge rating will go into service at the completion of bridge construction. The Bridge Preservation Section shall then be responsible to maintain an updated bridge load rating throughout the life of the bridge based on current bridge condition (see Appendix 14.0-A1). Conditions of existing bridges change resulting in the need for reevaluation of their load rating. Such changes may be caused by damage to structural elements, extensive maintenance or rehabilitative work, or any other deterioration identified by the Bridge Preservation Section through their regular inspection program. This criteria applies only to concrete and steel bridges. For timber bridges, rating procedure shall be as per Chapters 6 and 7 of the 1994 AASHTO Manual for Condition Evaluation of Bridges.
14.1.1
Rating Procedure Structural elements as defined above shall be evaluated for flexural, vertical shear, and torsional capacities based on Load Resistance Factor Design (LRFD) as outlined in the AASHTO 1989 Guide Specifications for Strength Evaluation of Existing Steel and Concrete Bridges and Load Factor Design (LFD) as outlined in the 1994 AASHTO Manual for Condition Evaluation of Bridges. Consider all reinforcing, including temperature/distribution reinforcing, in the rating analysis. By definition, the adequacy or inadequacy of a structural element to carry a specified truck load will be indicated by the value of its rating factor (RF); that is, whether it is greater or smaller than 1.0. For a specific loading, the lowest RF value of the structural elements will be the overall rating of the bridge.
August 1998
14.1-1
BRIDGE DESIGN MANUAL Criteria Bridge Rating 14.1.1.1
General
Load Resistance Factor Rating (LRFR) For HS-20, AASHTO-1, AASHTO-2, and AASHO-3 trucks, the basic rating equation shall be: φM CAP − γD M DL ± γP M P γL M ( L + I )
R.F. = (for flexure)
R.F. = (for vertical shear)
φV CAP − γDV DL ± γPV P γLV ( L + I )
For Overload (OL)-1 and Overload-2 trucks, the basic rating equation shall be:
( ) ( γL M(L+I) ) OL - Truck φV CAP − γDV D ± γPV P − ( γLV ( L + I ) ) AASHTO - Truck ( γLV(L+I) ) OL - Truck
φM CAP − γD M D ± γP M P − γL M ( L + I ) AASHTO - Truck
R.F. = (for flexure)
R.F. = (for vertical shear) Where: R.F.
=
Rating Factor (Ratio of Capacity to Demand)
MCAP
=
Ultimate Bending Moment Capacity
* MDL
=
Calculated Dead Load Bending Moment
MP
=
Secondary Bending Moment Due to Prestressing
* M(L+I)
=
Calculated Live Load and Impact Bending Moment
f
=
Resistance Factor (Capacity Reduction Factor)
γD
=
Dead Load Factor
γL
=
Live Load Factor
γP
=
Prestress Factor
I
=
Impact
VCAP
=
Ultimate Shear Capacity
VDL
=
Calculated Dead Load Shear Force
VP
=
Calculated Prestressing Shear Force
V(L+I)
=
Calculated Live Load Plus Impact Shear Force
*For continuous structures, a one-half support width moment increase is to be used.
14.1-2
August 1998
BRIDGE DESIGN MANUAL Criteria Bridge Rating 14.1.1.2
General
Load Factor Design Rating (LFDR) For HS-20 Inventory and HS-20 Operating Ratings, the basic equation shall be: R.F. =
φR n − A1D ± S A 2 L (1 + I )
Where: R.F.
=
Rating Factor (Ratio of Capacity to Demand)
φRn
=
Nominal Capacity of the Member
D
=
Unfactored Dead Load Moment or Shear
L
=
Unfactored Live Load Moment or Shear
S
=
Unfactored Prestress Secondary Moment or Shear
I
=
Impact Factor to Be Used With the Live Load Effect
A1
=
Factor for Dead Load (see Section 14.1.4.2)
A2
=
Factor for Live Load (see section 14.1.4.2)
Additional rating consideration shall be given to prestressed and post-tensioned members and is discussed in further detail in Section 14.2.1.2.
14.1.2
Live Loads The vehicles specified in the AASHTO Guide Specifications for Strength Evaluation of Existing Steel and Concrete Bridges represent legal weights and are to be used to determine posting limits. The two overload vehicles represent extremes in the limits of permitted vehicles in Washington State. The HS-20 vehicle and lane load as specified in the AASHTO Manual for Condition Evaluation of Bridges are to be used in reporting the inventory and operating ratings to the National Bridge Inventory. For new designs, the number of lanes shall be the actual designated lanes as shown on the bridge layout (not the number of lanes as per AASHTO Specification 3.6). For existing bridges, the number of lanes shall be the actual striped lanes at the time of rating. When multiple lanes are considered, apply the appropriate multilane reduction factor given in Section 14.1.7. Load distribution methods are discussed under specific bridge types. Do not consider sidewalk live loads in rating analysis.
14.1.2.1
Load Resistance Factor Rating (LRFR) The six moving loads for the initial rating shall be the HS-20 truck loading (Figure 14.1.2-4), three AASHTO vehicles and two overload trucks (Figure 14.1.2-1). In addition, use the lane loading as shown on Figure 14.1.2-2 to rate structures with spans over 200 feet. For the two overload trucks (OL-1 and OL-2), use only one overload truck occupying one lane in combination with one of the AASHTO trucks in each of the remaining lanes.
14.1.2.2
Load Factor Design Rating (LFDR) for National Bridge Inventory (NBI) The live load to be used in the basic rating equation should be the HS-20 truck (Figure 14.1.2-4) or lane loading (Figure 14.1.2-3) as defined in the AASHTO Design Specifications. Where the effects are greater than those produced by HS-20 truck, the bridge should also be rated using the lane loading.
August 1998
14.1-3
BRIDGE DESIGN MANUAL Criteria Bridge Rating 14.1.3
General
Dead Loads Dead Loads shall be as defined in the AASHTO Standard Specifications for Highway Bridges, except for concrete weight shall be 155 pcf. Dead Load shall include weight of any existing bridge deck overlay. When overlay depth is not known, allowance shall be as per Section 3.3.2.1 of the AASHTO Guide Specifications.
14.1.4
Load Factors
14.1.4.1
Load Resistance Factor Rating (LRFR) Dead Load
γD = 1.20
Prestress Load
γP = 1.00
Live Load* 1. 2. 3.
14.1-4
Low volume roadways (ADTT less than 1,000), significant sources of over weight trucks without effective enforcement.
γL = 1.65
Heavy volume roadways (ADTT greater than 1,000), significant sources of over weight trucks without effective enforcement.
γL = 1.80
OL-1 and OL-2 (or other permit vehicles).
γL = 1.30
August 1998
BRIDGE DESIGN MANUAL Criteria Bridge Rating
General
*Notes: If unavailable from traffic data, ADTT may be estimated as 20 percent of ADT. The listed factors are essentially the same as Table 2 of AASHTO Guide Specifications except that Live Load Category 1 and 2 have been eliminated based on the assumption that Washington State does not have fully effective enforcement or control of overloads.
Trucks for Rating (for LRFR)
Figure 14.1.2-1
August 1998
14.1-5
BRIDGE DESIGN MANUAL Criteria Bridge Rating
General Lane Load Rating (for LRFR)
Figure 14.1.2-2
Lane Load Rating (for LFDR)
Figure 14.1.2-3
HS-20 Truck (for both LRFR and LFDR)
Figure 14.1.2-4
14.1-6
August 1998
BRIDGE DESIGN MANUAL Criteria Bridge Rating 14.1.4.2
General
Load Factor Design Rating (LFDR) Dead Load Live Load
14.1.5
A1 = 1.30 A2 = 1.30 A2 = 2.17
Operating Inventory
Load Capacity Reduction Factors Use the evaluating procedures and equations found in the AASHTO Standard Specifications for Highway Bridges under the section on load factor design to determine nominal resistance. The following resistance factors (capacity reduction) apply only to structural members in good condition. Generally, condition of the structure and other pertinent information are listed on the Bridge Inspection Report and rating information sheets. The engineer should use this data to make adjustments to the resistance factors. For deck rating, the condition code found in field 8 (visual) of the old Bridge Inspection Report or 507 of the new Bridge Management Inspection Report should be used to adjust resistance factors. For superstructure rating, the lowest code of fields 14-19 of the old Inspection Report or fields 38 through 156 of the new Bridge Management Inspection Report should be used. Normally, adjustments can be made based on the AASHTO Guide Specifications Tables 3(a) and 3(b). Questions regarding interpretation of these tables should be directed to the Bridge Load Rating Engineer. For new designs, all ratable elements shall be considered an “8” for new condition. Resistance Factors: Redundant Steel Members: Nonredundant Steel Members: Prestressed Concrete Elements: Reinforced Concrete Elements:
φ0.95 φ0.80 φ0.95 flexure φ0.90 shear φ0.90 flexure φ0.85 shear
14.1.6
Impact
14.1.6.1
Load Resistance Factor Rating (LRFR) For new designs, impact shall be 10 percent (0.1). For existing bridges, the impact shall be determined by the approach roadway condition (field 33) and the amount of severe scaling on the bridge (field 12) as shown on the old Bridge Inspection Report or (field 533) and (field 512) respectively on the current Bridge Management Inspection Report. For approach roadway condition codes 6 or greater, assume 10 percent impact; for codes 5 or less, assume 20 percent impact. If the bridge has 0 to 4 percent severe scaling (S00 to S04 for the first three entries in field 12 or 512), assume 10 impact; if between 5 and 15 percent severe scaling, assume 20 percent impact; if greater than 15 percent severe scaling, assume 30 percent impact.
February 2000
14.1-7
BRIDGE DESIGN MANUAL Criteria Bridge Rating 14.1.6.2
General
Load Factor Rating (LFDR) Impact is expressed as a fraction of the live load stress, and shall be determined by the following formula: *I =
50 L + 125
Where: I = Impact Fraction (maximum 30%) L = Length in Feet of the Portion of the Span That is Loaded to Produce the Maximum Stress in the Member. *AASHTO Standard Specifications for Highway Bridges 3.8.2.1.
14.1.7
14.1.8
Reduction Factors (for both LRFR and LFDR) Number of Loaded Lanes
Reduction Factor
One or two lanes Three lanes Four lanes or more
1.0 0.8 0.7
Ratings for Overloads (LRFR) The OL-1 and OL-2 truck loads listed in Section 14.1.2 are considered to be overloads. Due to the infrequent nature of the overloads, it is more reasonable to use reduced live load factors for rating rather than those specified for design. For special cases, such as checking prestressed concrete members by the service load method, the rating factors should be established by using higher allowable stresses (see Section 14.2, Special Rating Criteria). For overload ratings, the load factors to be used in the basic rating equation shall be: γD
= 1.2
γL
= 1.3
γP
= 1.0
P:DP/BDM14 9807-0802
14.1-8
August 1998
BRIDGE DESIGN MANUAL Criteria Bridge Rating
General
14.2
Special Rating Criteria
14.2.1
Prestressed Concrete Bridges
14.2.1.1
Load Resistance Factor Rating (LRFR) For prestressed concrete members, rating is to be determined by the service load method for bending moments.* For prestressed girders designed for continuous of live load and impact, rate the negative moment zone at interior supports as a conventional reinforced concrete member, considering only the deck reinforcement (by load factor method). For loading conditions that produce positive moment at the supports, the prestressed girders extended strands can be considered as positive reinforcement. Rating for shear in the girder shall begin at a distance h/2 from the centerline of the pier (h = overall girder depth). When rating for AASHTO vehicles, allowable stresses shall be: Tensile stress for top and bottom = 6(f′c)1/2 Compressive stress = 0.4 f′c When rating for overload trucks (OL-1 and OL-2), allowable stresses shall be: Tensile stress for top and bottom = 1.15 [6(f′c)1/2] Compressive stress = 0.53 (1.3 f′c) For all loadings, prestress losses shall be as per design or current AASHTO Design Specifications. *When the rating for the overload vehicles is less than 1.0, a check by the ultimate load method shall also be made. The rating recorded on the summary sheet shall be the value determined by the ultimate load method divided by 1.30 but no greater than 1.0.
14.2.1.2
Load Factor Design (LFD) The rating of prestressed concrete members at both Inventory and Operating level should be established in accordance with the strength requirements of Article 9.17 of the AASHTO Design Specifications. Additionally at Inventory level, the rating must consider the allowable stresses at service load as specified in Article 9.15.2.2 of the AASHTO Design Specifications. In situations of unusual design with wide dispersion of the tendons, the operating rating might further be controlled by stresses not to exceed 0.90 of the yield point stresses in the prestressing steel nearest the extreme tendon fiber of the member. Typically, prestressed concrete members used in bridge structures will meet the minimum reinforcement requirements of Article 9.18.2.1 of the AASHTO Design Specifications. While there is no reduction in the flexural strength of the member and, in the event that these provisions are not satisfied, the Bridge and Structures office, may choose, as part of the flexural rating, to limit live loads to preserve the relationship between φMn and 1.2Mcr that is prescribed for a new design. The use of this option necessitates an adjustment to the value of the nominal moment capacity φMn, used in the flexural strength rating equations. Thus when φMn < 1.2Mcr, the nominal moment capacity becomes (k)φ(Mn), φM n
k = 1.2 M cr
August 1998
14.2-1
BRIDGE DESIGN MANUAL Criteria Bridge Rating
General
Inventory Rating To establish the Inventory rating for Prestressed Concrete, use the lowest rating factor from the basic rating equation, shown in Section 14.1.1.2, and the following equations: 6 (f ′ c )
12
R.F. = (Concrete Tension)
− F d + F p ± Fs F1
R.F. = (Concrete Compression)
0.6f ′ c − F d − F p ± F s F1
R.F. = (Concrete Compression)
0.4 f ′ c − 12 F d − F p ± F s F1
R.F. = (Prestressing Steel Tension)
(
)
(
)
0.8f ∗ y − F d + F p ± F s F1
Operating Rating To establish the operating rating for Prestressed Concrete, use the lowest rating factor, from the basic rating equation, shown in Section 14.1.1.2, and the following equation should be used: R.F. = (Prestressing Steel Tension)
(
0.9f ∗ y − F d + F p ± F s
)
F1
Where:
14.2.2
R.F.
=
Rating Factor (Ratio of Capacity to Demand)
f′c
=
Concrete Compressive Strength
Fd
=
Unfactored Dead Load Stress
Fp
=
Unfactored Stress Due to Prestress Forces After All Losses
Fs
=
Unfactored Stress Due to Secondary Prestress Forces
Fl
=
Unfactored Live Load Stress Including Impact
f*y
=
Prestress Steel Yield Stress (per AASHTO 9.1.2)
Reinforced Concrete Structures For conventional reinforced concrete members of existing bridges, checking of serviceability shall not be part of the rating evaluation. Rating for shear in the longitudinal direction shall begin at a distance h/2 from the centerline of the pier (h = total depth).
14.2.2.1
Concrete Decks For all concrete roadway deck slabs, except flat slab bridges, that are designed per current AASHTO criteria for HS-20 loading or heavier, loading will be considered structurally sufficient and need not be rated. However, for existing roadway slabs having any of the following conditions, rating will be required:
14.2-2
1.
Slab was designed for live loads lighter than HS-20.
2.
Slab overhang is more than half the girder spacing.
3.
Bridge Inspection Report Code is below 4 (field 8 or 508 — visual deck condition).
August 1998
BRIDGE DESIGN MANUAL Criteria Bridge Rating 4.
General When the original traffic barrier(s) or rail have been replaced by heavier barrier.
When rating of the slab is required, live load shall include all vehicular loads as specified in Section 14.1.2 and load distribution shall be per current AASHTO Standard Specifications for Highway Bridges.
14.2.2.2
Concrete Crossbeams For concrete crossbeams integral with the superstructure (raised crossbeam) on new bridges, rating will be for the number of designated lanes (see 14.1.2). For existing structures, ratings will be for the number of striped lanes. Live loads conforming to these lane configurations can be applied to the crossbeam as moving point loads at any location between curbs which produce the maximum effect. When rating for shear in crossbeams, current AASHTO Design Specifications requires shear design to be at the face of support if there is a concentrated load within a distance “d” from the face of support. This requirement is new relative to earlier editions of AASHTO Design Specifications which allowed shear reinforcement design to be at a distance “d” from the face of support. When rating existing crossbeams which show no indication of distress on the latest inspection report, but have a rating factor of less than one (1.0), a more detailed/accurate shear analysis should be performed. One acceptable method is the “truss analogy” as published in Bibliography 14.99-1(1). For existing box girder and integral T-beam crossbeams, in lieu of this detailed analysis, dead and live loads can be assumed as uniformly distributed and the shear rating performed at a distance “d” from the face of support.
14.2.2.3
In-Span Hinges For in-span hinges, rating for shear and bending moment should be performed based on the reduced cross-sections at the hinge seat. Diagonal hairpin bars are part of this rating as they provide primary reinforcement through the shear plane.
14.2.3
Concrete Box Girder Structures Rating shall be on the per bridge basis for all applied loads. This is consistent with the current design procedures regarding live load applications.
14.2.4
Concrete T-Beam Structures Rate on a per member basis, except for precast girder units, which are to be rated per unit.
14.2.5
Concrete Flat Slab Structures Rate cast-in-place solid slabs on a per foot of width basis. Rate precast panels on a per panel basis. Rate cast-in-place voided slabs based on a width of slab equal to the predominant center-to-center spacing of voids. Load distribution shall be per current AASHTO Standard Specifications for Highway Bridges. When rating flat slabs on concrete piling, assume pin-supports at the slab/pile interface of interior piers and the slab continuous over the supports. If ratings using this assumption are less than 1.0, the piles should be modeled as columns with fixity assumed at 10 feet below the ground surface. Pile caps are to be rated if deemed critical by the engineer.
14.2.6
Steel Structures On existing bridges, checking of fatigue and servicability shall not be part of the rating evaluation.
August 1998
14.2-3
BRIDGE DESIGN MANUAL Criteria Bridge Rating 14.2.6.1
General
Steel Floor Systems Floorbeams and stringers shall be rated as if they are simply supported. Assume the distance from outside face to outside face of end connections as the lengths for the analysis. For steel floorbeams on new bridges, rate for the number of designated lanes (see 14.1.2). For existing structures, rate for the number of striped lanes. Live loads conforming to these lane configurations can be applied to the floorbeam as moving point loads at any location between curbs which produce the maximum effect. The end connections for stringers and floorbeams shall be rated. Do not rate connections unless there is evidence of deterioration.
14.2.6.2
Steel Truss Structures The capacity of steel truss spans, regardless of length, shall follow the AASHTO Guide Specifications for Strength Design of Truss Bridges (load factor design) and the AASHTO Standard Design Specifications. In the event the two specifications are contradictory, the guide specification is to be followed. Rate on a per truss basis using either 3-D analysis or simplified distribution methods. Assume nonredundancy of truss members and pinned connections. In general, rate chords, diagonals, verticals, end posts, stringers, and floorbeams. Do not rate connections unless there is evidence of deterioration, except for pinned connections with trusses. For pin-connected trusses, also analyze pins for shear, and the side plates for bearing capacity. For truss members that have been heat-straightened three or more times, deduct 0.1 from φ(Phi).
14.2.7
Timber Structures Unless the species and grade is known, assume Douglas fir, select structural for members installed prior to 1955 and Douglas fir, No. 1 after 1955. The allowable stresses for beams and stringers, as listed in the AASHTO Standard Design Specifications, should be used. The inventory rating for HS-20 vehicle is calculated using allowable stresses as directed in the AASHTO Standard Design Specifications. For calculating the operating rating for the HS-20 vehicle, the 3 AASHTO, and two overload vehicles, use 133 percent of the inventory allowable stress. The nominal dimensions should be used to calculate deadload, and the net dimensions to calculate section modulus. If the member is charred, it may be assumed the 1/4-inch of material is lost on all surfaces. Unless the member is notched or otherwise suspect, shear need not be calculated. When calculating loads, no impact is assumed and distribution factors are selected assuming one traffic lane where the roadway is less than 20 feet wide or two or more traffic lanes where the roadway is 20 feet or wider.
14.2.8
Widened or Rehabilitated Structures For widened bridges, rate crossbeams in all cases. Since the longitudinal capacity of the widened portion of the structure will equal or exceed the capacity of the existing structure, a longitudinal rating for the widened portion will be required only when the width of the widened portion on one side of the structure is greater than or equal to 12′-0″ or more throughout the length of the structure. For rehabilitated bridges, a load rating will be required if the load carrying capacity of the structure is altered by the rehabilitation.
14.2-4
August 1998
BRIDGE DESIGN MANUAL Criteria Bridge Rating 14.2.9
General
Other Special Cases For nonredundant structures such as through girder, arches, and/or any superstructure with less than three main load carrying members, rating shall be on the per member basis.
P:DP/BDM14 9807-0802
August 1998
14.2-5
BRIDGE DESIGN MANUAL Criteria Bridge Rating
14.2-6
General
August 1998
BRIDGE DESIGN MANUAL Criteria Bridge Rating 14.3
General
Load Rating Software Use the current version of BRIDG for Windows software for all applicable ratings. The capabilities and release dates of the BRIDG software are as follows: Release Version
Release Date
Rating Capabilities
BRIDG v.105.
July 1996
LRFD and LF of concrete bridges.
BRIDG v.11.0.
December 1995
LRFD and LF of steel girder bridges.
BRIDG v.97
September 1997
LRFD and LF of concrete, steel girder, and steel truss bridges.
*Tenative release dates.
P:DP/BDM14 9807-0802
August 1998
14.3-1
BRIDGE DESIGN MANUAL Criteria Bridge Rating 14.4
General
Load Rating Reports Rating reports shall consist of: 1.
A Bridge Rating summary sheet as shown on Appendix 14.0-A5 reflecting the lowest rating factor, including superstructure components not analyzed by BRIDG, for each loading condition.
2.
A brief report of any anomalies in the ratings and an explanation of the cause of any rating factor below 1.0.
3.
Hard copy of computer output files (RPT files) used for rating, and any other calculations or special analysis required.
4.
A complete set of plans for the bridge.
5.
Two 3.5-inch data diskettes which contains the final versions of all input files (BDF files) created in performing the load rating.
All reports shall be bound in Accopress-type binders. When the load rating calculations are produced as part of a design project (new, widening, or rehabilitation,) the load rating report and design calculations shall be bound separately. Any questions on the BRIDG Program or load rating can be directed to the bridge Load Rating Engineer.
14.99
Bibliography 1.
Manual for Condition Evaluation of Bridges (1994) AASHTO, 444 North Capitol Street NW, Suite 249, Washington, D.C. 20001.
P:DP/BDM14 9807-0802
August 1998
14.4-1
BRIDGE DESIGN MANUAL Appendix A Bridge Rating
Load Rating Flow Chart
Bridge Designer complete Load Rating as part of Design Project
Load Rating turned into Bridge Project Unit
Load Rating sent to Load Rating Engineer
No
S&E schedule distributed monthly to Load Rating Engineer
Complete
yes
List of missing Load Ratings Distributed quarterly to the Bridge Design Engineer
Load Rating Engineer tracks Load Ratings
Load Rating Engineer Update Database and File Load Rating
14.0-A1 Load Rating Flow Chart
August 1998
14.0-A1
BRIDGE DESIGN MANUAL Appendix A Bridge Rating
Source of Rating Factors
14.0-A2 Source of Rating Factors
14.0-A2
August 1998
BRIDGE DESIGN MANUAL Appendix A Bridge Rating
Bridge Inspection Report Condition Codes Bridge Inspection Report Condition Codes
9
Not applicable.
8
Very good condition. No defects. Bridge can carry normal traffic levels. No action required to monitor or repair.
7
Good condition. Minor defects with potential for minor repair. Bridge can carry normal traffic levels. Record and monitor bridge conditions.
6
Satisfactory condition. Moderate defects with potential for major repair. Bridge is adequate for normal traffic levels. Record and monitor bridge conditions and/or add to repair schedule.
5
Fair condition. Moderate defects with potential for minor rehabilitation. Bridge is minimally adequate for highway traffic. Monitor bridge conditions and/or add to repair schedule.
4
Poor Condition. Major defects requiring major repair. Bridge is marginally adequate for truck traffic. Make repairs as soon as possible.
3* Serious condition. Major defects. Member is failing. Bridge is inadequate for truck traffic. Repair bridge immediately or restrict truck traffic. 2* Critical condition. Major defects. Member has failed. Bridge is inadequate for all highway traffic. Repair bridge immediately or close bridge. 1* Imminent failure. Bridge is closed and inadequate for all highway traffic. Bridge cannot be rehabilitated. 0* Failed. Bridge is closed and inadequate for all highway traffic. Bridge is beyond repair. *These codes are used to rate the condition of primary bridge members only (i.e., trusses, beams, abutments, etc.). For changing values in the rating factor equation, a condition code of 7 or 8 corresponds to good or fair condition. A condition code of 5 or 6 corresponds to a deteriorated condition; generally the report would identify the deficient structural elements with specifics such as section loss. A condition code of 4 or less corresponds to a heavily deteriorated condition. The report should state the specific element with its section loss. Inspection is considered to be estimated except in a specific case associated with identifiable deteriorated and/or deteriorating structures. Maintenance is considered intermittent unless specifically directed in unusual circumstances.
August 1998
14.0-A3
BRIDGE DESIGN MANUAL Appendix A Bridge Rating
Span Type Abbreviations Span Type Abbreviations
BAS
Bascule Lift Span
SA
Steel Arch
CA
Concrete Arch
SB
Steel Beam
CBOX
Concrete Box Girder
SBOX
Steel Box Girder
CFP
Concrete Floating Pontoon
SCULV
Steel Culvert
CG
Concrete Girder
SFP
Steel Floating Pontoon
CS
Concrete Slab
SG
Steel Girder
CST
Concrete Slab on Timber Piling
SL
Steel Lift Span
CTB
Concrete T-Beam
SS
Steel Swing Span
CTRU
Concrete Truss
ST
Steel Truss
CTUN
Concrete Lined Tunnel
SUSP
Steel Suspension Span
CCULV
Concrete Culvert
TCULV
Timber Culvert
ESB
Encased Steel Beam
TTLB
Treated Timber Laminated Beam
PCB
Pretensioned Concrete Beam
TTLL
Treated Timber Longitudinal Laminated
PCS
Pretensioned Concrete Slab
TTRU
Treated Timber Truss
PCTB
Pretensioned Concrete T-Beam
TTS
Salts-Treated Timber Trestle
POB
Post-tensioned Concrete Beam
TTT
Creosote-Treated Timber Trestle
POTB
Post-tensioned Concrete T-Beam
TTUN
Timber-Lined Tunnel
PTBX
Post-tensioned Box Girder
TUN
Tunnel
PRC
Precast Reinforced Concrete Beam
UTL
Untreated Log
PRPOB
Pretensioned and Post-tensioned Beam
UTRU
Untreated Timber Truss
UTT
Untreated Timber Trestle
UTLB
Untreated Timber Laminated Beam
14.0-A4
August 1998
BRIDGE DESIGN MANUAL Appendix A Bridge Rating
Bridge Rating Summary Bridge Rating Summary
Bridge Name: _________________________________________________________________________________ Bridge Number: _______________________________________________________________________________ Span Types: __________________________________________________________________________________ Bridge Length: ________________________________________________________________________________ Design Load: _________________________________________________________________________________ Rating By: ___________________________________________________________________________________ Checked By: __________________________________________________________________________________ Date: ________________________________________________________________________________________
Truck
RF
γ
HS-20
_________________
_________________
_____________________________
AASHTO 1
_________________
_________________
_____________________________
AASHTO 2
_________________
_________________
_____________________________
AASHTO 3
_________________
_________________
_____________________________
OL-1
_________________
_________________
_____________________________
OL-2
_________________
_________________
_____________________________
Inventory
_________________
_________________
_____________________________
Operations
_________________
_________________
_____________________________
Controlling Point
NBIS Rating
Remarks: _____________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________ ____________________________________________________________________________________________
August 1998
14.0-A5
BRIDGE DESIGN MANUAL Appendix A Bridge Rating
Load Rating Flow Chart
3D Live Load Modeling Guidelines for Truss Bridges Live Load Criteria The live loads to be considered and the application thereof, shall be consistent with those described in the AASHTO Guide Specifications for Strength Evaluation of Existing Steel and concrete Bridges and the WSDOT Bridge Design Manual. To summarize the criteria: • In computing load effects, one vehicle shall be considered present in each rating lane. • The positioning of the vehicle in each rating lane shall be according to AASHTO specifications. These specifications require the vehicle to be positioned in such a way as to produce the extreme structural response under consideration. • For the purpose of load rating, the number of rating lanes shall be considered the number of striped lanes. • The rating lanes shall be positioned between the curbs in accordance with the AASHTO specifications.
Live Load Modeling Guidelines The purpose of these guidelines is to provide the rating engineer with a live load modeling scheme that will capture the significant load effects for typical, well conditioned truss bridges, while reducing the time required to perform a detailed live load analysis. Typical truss bridges are symmetrical about their longitudinal axes, with parallel trusses, straight members, and uniform spacing of floor beams. It is ultimately the responsibility of the rating engineer to determine the minimum rating factor for the structure. For unique and/or poorly conditioned structures, this may require a more detailed evaluation of the live load effects. BRIDG™ for Windows® implements a brute force live load analysis method. To improve live load analysis performance, the generation of live load cases must be reduced. These guidelines describe live load generation in terms of longitudinal step sizes for the movement of the trucks along the bridge and transverse lane positions between the curb lines.
Minimum Longitudinal Step Size Longitudinal step shall not be less than the distance between floor beams.
Transverse Placement of Rating Lanes The transverse placement of rating lanes is guided by the Lane Shift Sensitivity Factor (LSSF). This factor is used to determine if the response of the structure is sensitive to lane positioning. The Lane Shift Sensitivity Factor is computed by: LSSF = (# of Design Lens - # of Rating Lanes) / # of Rating Lanes Where: Number of rating Lanes is the equal to the number of lanes currently striped on the bridge. Number of Design Lanes is as specified by the AASHTO Standard Specification for Bridges.
14.0-A6
August 1998
BRIDGE DESIGN MANUAL Appendix A 3D Live Load Modeling Guidelines for Truss Bridges
Bridge Rating The position of rating lanes is described in the following table:
Sensitivity
LSSF
Lane Group Positioning
Insensitive
LSSF < 0.25
Center of the bridge
Sensitive
0.25 ≤ LSSF ≤ 1.0
Left Edge, Center, Right Edge
Hypersensitive
LSSF > 1.0
Left Edge, Left Quarter Point, Center, Right Quarter Point, Right Edge
This method of transverse placement will be used to determine the Inventory and Operating Ratings for reporting to the National Bridge Inventory. This method will also be used to determine if the bridge needs further investigation by the WSDOT Bridge Preservation office. This investigation will determine the need for posting, restriction to permit (a.k.a. overload) vehicles, and need for retrofit or rehabilitation.
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August 1998
14.0-A7