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Highway Bridge Design for Beginners

Dr. M. Azhar Saleem May 10, 2016 One Day, 1 CPD Point Seminar

Department of Civil Engineering University of Engineering and Technology Lahore, Pakistan

Introduction Outline – Part A, Dr. Azhar Saleem ◦ ◦ ◦ ◦

Introduction to Bridges and Bridge Aesthetics AASHTO LRFD Bridge Design Specifications West Pakistan Highway Code of Practice Deck analysis and design

Outline – Part B, Engr. Hafiz M. Ahmad ◦ General Design Considerations ◦ Prestressed girder – Analysis and Design ◦ Substructures 2

Introduction References











Barker M. and Puckett J., Design of Highway Bridges, An LRFD Approach, 2nd Ed, Wiley & Sons, 2007. AASHTO LRFD Bridge Design Specification, 5th Edition, 2010. Tonias D. and Zhao J., Bridge Engineering, 2nd Edition, Mc Graw-Hill, 2007. Leonardo Fernández Troyano, Bridge Engineering: a global perspective, Thomas Telford, Ltd, 2003. Menn, Christian, Prestress Concrete Bridges, Birkhäuser Verlag, 1990. Nigel R. Hewson, Prestressed Concrete Bridges: Design and Construction, Thomas Telford, Ltd, 2003. Schlaich J. and Scheef H., Concrete Box Girder Bridges, IABSE, 1982. Publications by FHWA, www.fhwa.org Publications by AASHTO, lrfd.aashtoware.org Publications by the National Steel Bridge Alliance, www.steelbridge.org

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Bridges…Definition


Bridges are structures that connect and/or cross two points separated by a road, river or valley.




In social terms they connect communities, nations, races, etc. and are sign of friendship and peace.




In structural terms, bridges are fascinating structures, a source of challenge to engineers and builders.




In many respects, bridge engineers can express their talent through these art forms and sculptures.

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Bridges…Design


Bridges are essential elements of a transportation network since they control the capacity of the system, and as such they should be carefully planned and engineered.




Unlike other structural systems, bridge design depends on how the different bridge components (deck, girders, etc) are put together or built. In some cases, loads generated during bridge construction control the member sizes. Hence, special attention shall be given on how a bridge is built and shall be clearly expressed or described in contractual documents.

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Bridges Do Not Just Happen They must be planned and Engineered Before They can be Constructed 6

Transportation Project Financing

Procurement

Design

Planning

Construction

Project

Maintenance

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Bridge Engineering

Design ProcessProcess-1 Phase 1: Owner’s Requirements

Functional

Aesthetics

Budget

Design Criteria

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Bridge Engineering

Design ProcessProcess-2 Phase 2: Design Development Preliminary Designs Development of Alternatives

Selection of Recommended Alternative

Adequate

Cost Effective

Constructible and Maintainable 9

Bridge Engineering

Design ProcessProcess-3 Phase 3: Contract Plans Structural Analysis

Structural Design

Plan Production

Specifications and Bid Documents 10

Construction Process





Construction Engineering ◦ Shop drawings production ◦ Construction analysis ◦ False work design Construction ◦ Crew efficiency ◦ Geometry control ◦ Storage ◦ Equipment staging ◦ Temporary bracing ◦ Maintenance of Traffic (MOT) ◦ Erection sequence ◦ Casting 11

Types of Bridges







Slab-on-stringer (95% of all types) Steel and Concrete Box Girders Steel and Concrete Arch Trusses Moveable (Lift, bascule and swing etc.) Suspension

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Bridge Engineering

Types of Bridges

Slab on Stringer

Box Girder

Arch

Truss

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Bridge Engineering

Types of Bridges

Bascule

Lift

Moveable Bridge

Swing

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Bridge Engineering

Types of Bridges Golden Gate Bridge

Suspension Bridge 15

Types of Bridges

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Bridge Engineering

Span Rang

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Bridge Engineering

Bridge Selection

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Bridge Engineering

Bridge Components

The stone clapper Darth River (Dartmoor) bridge, built in 111 BC by Celtic tribes of Scotland is shown above. It has the same fundamental elements of a modern highway bridge: a super-structure and a substructure. The stones are quality grade granite. 19

Bridge Components


Julius Caesar’s temporary bridge across the Rhine in 56 BC, was built in 3 days, and then dismantled in one day after a successful campaign in Germany. (“The Conquest of Gaul”, by J. Caesar, 50 BC).




Note the basic elements still present in today’s bridges.

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Bridge Components

The Roman aqueduct/bridge Pont du Gard in France is over 19 21 centuries old

Bridge Components

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Bridge Engineering

Bridge Components

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Bridge Engineering

Bridge Components

End Bent

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Bridge Engineering

Bridge Components

Typical Components of Box Girder Bridge

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Bridge Engineering

Bridge Components

Typical Components of Composite I-girder Bridge

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Bridge Engineering

Bridge Components

A modern slab-on-stringer highway bridge, with steel stringers and lateral bracing

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Bridge Engineering

Bridge Components

Welded curved steel stringers.

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Bridge Components

Elements of Substructure

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Bridge Aesthetics

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Bridge Aesthetics


Architects




Landscape Artists




Illumination Experts

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Hegel Said: It is impossible to discover a rule that can be used to judge what is beautiful and what is not.

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AASHTO LRFD Bridge Design Specifications

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American Association of State Highway Officials (AASHO (AASHO)) Founded on:

Dec. 12, 1914 Standard Specifications for Highway Bridges and Incidental Structures,

1931 41

In 1963, AASHO became

TO

AASH

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History of Bridge Codes in USA











From 1931 to 2002 the American Association of State Highway and Transportation Officials (AASHTO) published the Standard Specifications for Design of Highway Bridges (17 Eds.). Updates in the form of interims were done annually In the late 1970’s, the Ontario Ministry of Transportation published limit-state design bridge specifications. In 1986, the American Institute of Steel Construction (AISC) published the LRFD Manual of Steel Construction In 1988, NCHRP 12-33 sponsored the “Development of Comprehensive Specifications and Commentary” In 1994, the AASHTO LRFD Specifications for Design of Highway Bridges, Ist Edition, was published.

AASHTO LRFD, 7th Ed. , 2016 is the Latest 43

American Association of State Highway and Transportation Officials (AASHTO (AASHTO)) AASHTO is a nonprofit, nonpartisan association highway and transportation representing departments in the 50 states, the District of Columbia, and Puerto Rico. It represents all five transportation modes: air, highway, public transportation, rail, and water. Its primary goal is to foster the development, operation, and maintenance of an integrated national transportation system

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American Association of State Highway and Transportation Officials (AASHTO (AASHTO))

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AASHTO LRFD Bridge Design Specifications The provisions of these specifications are intended for the design, evaluation, and rehabilitation of both fixed and movable highway bridge. Horizontally curved concrete girders are not fully covered and were not part of calibration data. These specifications are not intended to supplant proper training or exercise of judgment by designer, and state only minimum requirements necessary to provide for public safety. AASHTO 1.1

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More than 2000 Pages

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Bridge Engineering

AASHTO LRFD Bridge Design Specifications Bridge: Any structure having an opening not less than 20 ft. that forms part of a highway or that is located over or under a highway Design Life: Period of time on which the statistical derivation of transient load is based: 75 years for these specification. Ductility: Property of a component or connection that allows inelastic response. Extreme Event Limit States: Limit states relating to events such as earthquakes, ice load, and vehicle and vessel collision, with return periods in excess of the design life of the bridge AASHTO 1.2

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Bridge Engineering

AASHTO LRFD Bridge Design Specifications Factored Load: The nominal loads multiplied by the appropriate load factors specified for the load combination under consideration. Factored Resistance: The nominal resistance multiplied by the resistance factor. Limit State: A condition beyond which the bridge or component ceases to satisfy the provisions for which it was designed. Load and Resistance Factor Design (LRFD): A reliability-based design methodology in which force effects caused by factored loads are not permitted to exceed the factored resistance of components AASHTO 1.2

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Bridge Engineering

AASHTO LRFD Bridge Design Specifications Load Factor: A statistically-based multiplied applied to force effects accounting primarily for variability of loads, the lack of accuracy in analysis, and probability of simultaneous occurrence of different loads, but also related statics of the resistance through the calibration process. Nominal Resistance: Resistance of a component or connection to force effects, as indicated by the dimensions specified in the contract documents and by permissible stress, deformations, or specified strength of materials. Resistance Factor: A statistically-based multiplier applied to nominal resistance accounting primarily for variability of material properties, structural dimensions and workmanship, and uncertainty in the prediction of resistance, but also related to statistics of the loads through the calibration process. AASHTO 1.2

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Bridge Engineering

AASHTO LRFD Bridge Design Specifications Regular Service: Condition excluding the presence of special permit vehicles, wind exceeding 55 mph, and extreme events, including scour. Service Life: The period of time that the bridge is expected to be in operation. Service Limit States: Limit states relating to stress, deformation and cracking under regular operating conditions. Strength Limit States: Limit states relating to strength and stability during the design life. AASHTO 1.2

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Design ApproachApproach-AASHTO In the beginning, the design philosophy utilized in the Standard Specification was Allowable Stress Design. In the 1970s, variations in the uncertainties of loads were considered and Load Factor Design was introduced as an alternative method.

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Load and Resistance Factor Design (LRFD) LRFD is the prevailing method for design of bridges structures. This is reliability-based methodology which uses state-of-the-art analysis and design technique. The l0ad and resistance factor are calibrated from actual bridge statistics to ensure a uniform level of safety. Modern codes around the world use this design philosophy which leads to superior serviceability.

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AASHTO LRFD Survey in the U.S.A. May 2006

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Move to AASHTO LRFD Specification

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Design Philosophy The current design philosophy used the same principles as in concrete buildings (ACI) and steel (AISC), that factoring loads and adjusting resistance: LRFD

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Strength--I Limit State Strength (Load Combination)

1.75 LL + 1.25 DC + 1.5 DW

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Influence Lines

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Influence Lines


Influence lines are graphical representations of the effect of moving loads (live loads) in structural systems. They are represented by a unit load of variable position at a given point in the structural system,. These diagrams are used to compute the maximum response at a given section in the structures.

Influence lines play a primary role in structures subjected to moving load, such as bridges, industrial crane rails, and systems where loads move across spans.

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ILD for Moment

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Maximum Positive Moment

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Bridge System Analysis A bridge is a 3-D structure that in addition to gravity loads is subjected to moving loads. A full blown analysis will require the use of finite element methods, however, for many years bridge engineering practice has reduce the computational effort by a more manageable and simpler structural modeling.

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Bridge System Analysis AASHTO LRFD provides a simplified way of computing effects of moving loads. This approximate model is called Line Girder Analysis. Line girder analysis is simple to understand and calculate, however, the big unknown is, how to compute the effects of moving loads? These effects are obtained through what is called as

Distribution

Factor. The distribution factor is defined as the ratio of a maximum effect (shear and moment) to the simplified results of a line girder (onedimensional analysis). 64

Move to AASHTO LRFD Specification

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AASHTO Design Procedure for Distribution Factors To determine the moment and shear in a particular beam: 1. Compute moment and shear per lane 2. Compute distribution factor for both M and V (DFm and DFv) 3. Add IM – only to truck and/or tandem 4. Determine the moment and shear for the specified beam

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AASHTO Design Procedure for Distribution Factors M LL+IM = DFM x MLL+IM (Lane) VLL+IM = DFV x VLL+IM (Lane)

The DF for AASHTO LRFD tables already include the multipresence factor m. If using lever rule, add factor m. 67

Move to Example in the Handout

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Deck Design

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Deck Design


Empirical Design Method (9.7.2)




Traditional Method (9.7.3)

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Move to AASHTO

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Empirical Design Method


Bottom Reinforcement = 0.27 in2/ft

◦#6@18” c/c ◦#4@8” c/c


Top Reinforcement = 0.18 in2/ft

◦#4@12c/c ◦ Bar spacing < 18” 72

Tradition Design Methods

Move to AASHTO

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Concluded

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