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SPECIFICATION FOR THE DESIGN OF COLD-FORMED STEEL STRUCTURAL MEMBERS With Commentary 1996 EDITION SUPPLEMENT NO. 1 July 30, 1999

American Iron and Steel Institute

SPECIFICATION FOR THE DESIGN OF COLD-FORMED STEEL STRUCTURAL MEMBERS 1996 EDITION SUPPLEMENT NO. 1

American Iron and Steel Institute

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Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

The material contained herein has been developed by the American Iron and Steel Institute Committee on Specifications for the Design of Cold-Formed Steel Structural Members. The Committee has made a diligent effort to present accurate, reliable, and useful information on cold-formed steel design. The Committee acknowledges and is grateful for the contributions of the numerous researchers, engineers, and others who have contributed to the body of knowledge on the subject. Specific references are included in the Supplement to the Commentary on the Specification. With anticipated improvements in understanding of the behavior of cold-formed steel and the continuing development of new technology, this material may eventually become dated. It is anticipated that AISI will publish updates of this material as new information become available, but this can not be guaranteed. The materials set forth herein are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered professional engineer. Indeed, in most jurisdictions, such review is required by law. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.

1st Printing – April 2000

Produced by American Iron and Steel Institute Washington, DC Copyright American Iron and Steel Institute 2000

Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

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TABLE OF CONTENTS AISI 1996 SPECIFICATION FOR THE DESIGN OF COLD-FORMED STEEL STRUCTURAL MEMBERS SUPPLEMENT NO. 1 Section A3.1........................................................................................................................................................ 5 Section A3.3........................................................................................................................................................ 5 Section A5.1.3 ..................................................................................................................................................... 6 Section A9........................................................................................................................................................... 6 Section B1.1 ........................................................................................................................................................ 7 Section B2.4 ........................................................................................................................................................ 7 B2.4 C-Section Webs With Holes Under Stress Gradient ............................................................... 7 Section B6.1 ........................................................................................................................................................ 8 Section C2 ........................................................................................................................................................... 8 C2 Tension Members .................................................................................................................... 8 Section C3.1 ........................................................................................................................................................ 9 Section C3.1.2 ..................................................................................................................................................... 9 C3.1.2.1 Lateral-Torsional Buckling Strength for Open Cross Section Members................................. 9 C3.1.2.2 Lateral-Torsional Buckling Strength for Closed Box Members............................................ 11 Section C3.1.3 ................................................................................................................................................... 12 C3.1.3 Beams having One Flange Through-Fastened to Deck or Sheathing.................................... 12 Section C3.1.4 ................................................................................................................................................... 13 Section C3.1.5 ................................................................................................................................................... 13 C3.1.5 Strength for Standing Seam Roof Panel Systems.................................................................. 13 Section C3.2 ...................................................................................................................................................... 14 C3.2.2 Shear Strength of C-Section Webs With Holes..................................................................... 14 Section C3.4 ...................................................................................................................................................... 15 C3.4.2 Web Crippling Strength of C-Section Webs With Holes ...................................................... 15 Section C3.5.1 ................................................................................................................................................... 16 Section C4 ......................................................................................................................................................... 16 Section C6.1 ...................................................................................................................................................... 16 Section C6.2 ...................................................................................................................................................... 16 Section D3.2.1 ................................................................................................................................................... 16 Section D3.3...................................................................................................................................................... 17 Section E2.6 ...................................................................................................................................................... 17 Section E2.7 ...................................................................................................................................................... 18 E2.7 Shear Lag Effect in Welded Connections of Members Other Than Flat Sheets ................... 18 Section E3.2 ...................................................................................................................................................... 18 E3.2 Shear Lag Effect in Bolted Connections ............................................................................... 18 Section E3.3 ...................................................................................................................................................... 20 Section E5 ......................................................................................................................................................... 20 E5.2 Tension Rupture .................................................................................................................... 21 E5.3 Block Shear Rupture.............................................................................................................. 21 Section E6.1 ...................................................................................................................................................... 21 Section F1.......................................................................................................................................................... 21 APPENDIX A: Base Test Method for Purlins Supporting a Standing Seam Roof System.............................. 23 APPENDIX B: Standard Procedures for Panel and Anchor Structural Tests .................................................. 31

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Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

TABLE OF CONTENTS COMMENTARY ON AISI 1996 SPECIFICATION FOR THE DESIGN OF COLD-FORMED STEEL STRUCTURAL MEMBERS SUPPLEMENT NO. 1 Section A3.1...................................................................................................................................................... 37 Section A3.3...................................................................................................................................................... 37 Section A7.1...................................................................................................................................................... 38 Section A8......................................................................................................................................................... 38 Section B2.4 ...................................................................................................................................................... 38 B2.4 C-Section Webs With Holes Under Stress Gradient ............................................................. 38 Section B6.1 ...................................................................................................................................................... 39 Section C2 ......................................................................................................................................................... 40 C2 Tension Members .................................................................................................................. 40 Section C3.1.2 ................................................................................................................................................... 40 C3.1.2.1 Lateral-Torsional Buckling Strength for Open Cross Section Members............................... 40 C3.1.2.2 Lateral-Torsional Buckling Strength for Closed Box Members............................................ 45 Section C3.1.3 ................................................................................................................................................... 45 Section C3.1.4 ................................................................................................................................................... 45 Section C3.1.5 ................................................................................................................................................... 46 C3.1.5 Strength for Standing Seam Roof Panel Systems.................................................................. 46 Section C3.2 ...................................................................................................................................................... 47 C3.2.2 Shear Strength of C-Section Webs With Holes..................................................................... 47 Section C3.4 ...................................................................................................................................................... 47 C3.4.2 Web Crippling Strength of C-Section Webs With Holes ...................................................... 48 Section C4 ......................................................................................................................................................... 48 Section C6.1 ...................................................................................................................................................... 49 Section C6.2 ...................................................................................................................................................... 49 Section D3.2.1 ................................................................................................................................................... 49 Section D3.3...................................................................................................................................................... 49 Section E2 ......................................................................................................................................................... 50 Section E2.6 ...................................................................................................................................................... 51 Section E2.7 ...................................................................................................................................................... 51 E2.7 Shear Lag Effect in Welded Connections of Members Other Than Flat Sheets ................... 51 Section E3.2 ...................................................................................................................................................... 51 Section E3.3 ...................................................................................................................................................... 52 Section E5 ......................................................................................................................................................... 53 E5 Fracture.................................................................................................................................. 53 Section E6.1 ...................................................................................................................................................... 54 Section F1.......................................................................................................................................................... 54 Section F3.3....................................................................................................................................................... 54 REFERENCES ................................................................................................................................................. 54

Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

AISI 1996 SPECIFICATION FOR THE DESIGN OF COLD-FORMED STEEL STRUCTURAL MEMBERS SUPPLEMENT NO. 1 JULY 30, 1999 1.

Section A3.1 •

Update the titles of ASTM A611 and A653/A653M as follows: ASTM A611 (Grades A, B, C, and D), Structural Steel (SS), Sheet, Carbon, ColdRolled ASTM A653/A653M (SS Grades 33, 37, 40, and 50 Class 1 and Class 3; HSLAS Types A and B, Grades 50, 60, 70 and 80), Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process

•

Add ASTM A847 and ASTMA875/A875M to the section: ASTM A847 Cold-Formed Welded and Seamless High Strength, Low Alloy Structural Tubing with Improved Atmospheric Corrosion Resistance ASTM A875/A875M (SS Grades 33, 37, 40, and 50 Class 1 and Class 3; HSLAS Types A and B, Grades 50, 60, 70, and 80), Steel Sheet, Zinc-5% Aluminum Alloy-Coated by the Hot-Dip Process

2.

Section A3.3 • •

Move the first footnote on page V-26 to the Commentary (See Supplement to the Commentary for details). Revise Section A3.3.2 as follows: A3.3.2 Steels conforming to ASTM A653 SS Grade 80, A611 Grade E, A792 Grade 80, A875 SS Grade 80 and other steels which do not meet the provisions of Section A3.3.1 shall be permitted for multiple-web configurations such as roofing, siding and floor decking provided that: (1) the yield point, Fy, used for determining nominal strength in Chapters B, C, and D is taken as 75 percent of the specified minimum yield point or 60 ksi (414 MPa), whichever is less, and (2) the tensile strength, Fu, used for determining nominal strength in Chapter E is taken as 75 percent of the specified minimum tensile strength or 62 ksi (427 MPa), whichever is less. Alternatively, the suitability of such steels for any configuration shall be demonstrated by load tests according to the provisions of Section F1. Design strengths based on these tests shall not exceed the strengths calculated according to Chapters B through E, using the specified minimum yield point, Fy, and the specified minimum tensile strength, Fu. Exception: For multiple-web configurations, a reduced yield point, RbFy, shall

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Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

be permitted for determining the nominal flexural strength in Section C3.1.1(a), for which the reduction factor, Rb, shall be determined as follows: (a) Stiffened and Partially Stiffened Compression Flanges For w t ≤ 0.067 E Fy Rb = 1.0 For 0.067 E Fy < w t < 0.974 E Fy Rb = 1 − 0.26 [wFy ( tE) − 0.067]0.4

(Eq. A3.3.2-1)

For 0.974 E Fy ≤ w t ≤ 500 Rb = 0.75 (b) Unstiffened Compression Flanges For w t ≤ 0.0173E Fy Rb = 1.0 For 0.0173E Fy < w t ≤ 60 Rb = 1.079 − 0.6 wFy /( tE)

(Eq. A3.3.2-2)

where E = Modulus of elasticity Fy = Yield point as specified in Section A7.1 ≤ 80 ksi (552 MPa) t = Thickness of section w = Flat width of compression flange The above Exception Clause does not apply to the use of steel deck for composite slabs, for which the steel deck acts as the tensile reinforcement of the slab.

3.

Section A5.1.3 Revise the whole section as follows: When the seismic load model specified by the applicable code or specification is limit state based, the resulting earthquake load (E) shall be permitted to be multiplied by 0.67. Additionally, except for Section D5, when the load combinations specified by the applicable code or specification or Section A5.1.2 include wind or earthquake loads, the resulting forces shall be permitted to be multiplied by 0.75.

4.

Section A9 Update the referenced documents as follows: • In the fourth referenced document, change “AWS D1.3-89” to “AWS D1.3-98”. • Update the ASTM Standards as follows: • Change “ASTM A242/A242M-93a” to “ASTM242/A242M-97”, • Change “A283/A283M-93a” to “A283/A283M-97”, • Change “A307-94a” to “A307-97”, • Change “A325-94” to “A325-97”, • Change “A325M-93” to “A325M-97”, • Change “A354-95” to “A354-97”, • Change “A370-95” to “A370-97a”, • Change “A490-93” to “A490-97”,

Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

• • • • • • • • • • • • • • • • • 5.

Change “A500-93” to “A500-98”, Change “A529/A529M-94” to “A529/A529M-96”, Change “A563-94” to “A563-96”, Change “A563M-94” to “A563M-97”, Change “A570/A570M-95” to “A570/A570M-96”, Change “A572/A572M-94c” to “A572/A572M-98”, Change “A588/A588M-94” to “A588/A588M-97”, Change “A606-91a” to “A606-97”, Change “A607-92a” to “A607-96”, Revise the ASTM A611 title to “ASTM A611-97, Structural Steel (SS), Sheet, Carbon, Cold-Rolled”, Change “A653/A653M-95” to “A653/A653M-97”, and change “(Galvanealed)” to “(Galvannealed)”, Change “A715-92a” to “A715-96”, Change “ASTM A792/A792M-95” to “ASTM A792/A792M-97”, Add “ASTM A847-93, Cold-Formed Welded and Seamless High Strength, Low Alloy Structural Tubing with Improved Atmospheric Corrosion Resistance”, Add “ASTM A875/A875M-97 (SS Grades 33, 37, 40, and 50 Class 1 and Class 3; HSLAS Types A and B, Grades 50, 60, 70, and 80), Steel Sheet, Zinc-5% Aluminum Alloy-Coated by the hot-Dip Process”, Change “F959-95” to “F959-96”, and Change “F959M-95” to “F959M-96”.

Section B1.1 Revise three conditions as follows: (1) Stiffened compression element having one longitudinal edge connected to a web or flange element, the other stiffened by: Simple lip 60 Any other kind of stiffener i) when Is < Ia 60 ii) when Is ≥ Ia 90 (2) Stiffened compression element with both longitudinal edges connected to other stiffened elements 500 (3) Unstiffened compression element 60

6.

Section B2.4 Add the following new section: B2.4 C-Section Webs With Holes Under Stress Gradient These provisions shall be applicable within the following limits: (1) d0 / h < 0.7 (2) h / t ≤ 200 (3) Holes centered at mid-depth of the web (4) Clear distance between holes ≥ 18 in. (457 mm) (5) Non-circular holes, corner radii ≥ 2t

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Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

(6) Non-circular holes, d0 ≤ 2.5 in. (64 mm) and b ≤ 4.5 in. (114 mm) (7) Circular hole diameters ≤ 6 in. (152 mm) (8) d0 > 9/16 in. (14 mm) (a) Strength Determination When d0/h < 0.38, the effective widths, b1 and b2, shall be determined by Section B2.3(a) by assuming no hole exists in the web. When d0/h ≥ 0.38, the effective width shall be determined by Section B3.1(a) assuming the compression portion of the web consists of an unstiffened element adjacent to the hole with f = f1 as shown in Figure B2.3-1. (b) Deflection Determination The effective widths shall be determined by Section B2.3(b) by assuming no hole exists in the web. where d0 = Depth of web hole b = Length of web hole b1, b2 = Effective widths defined by Figure B2.3-1 h

7.

= Depth of flat portion of the web measured along the plane of the web

Section B6.1 Change “0.37” in the last paragraph to “0.42”.

8.

Section C2 Revise the whole section as follows: C2 Tension Members For axially loaded tension members, the nominal tensile strength, Tn, shall be the smallest value obtained according to the limit states of (a) yielding in the gross section, (b) fracture in the net section away from connections, and (c) fracture in the effective net section at the connection: (a) For yielding: (Eq. C2-1) Tn = AgFy Ωt = 1.67 (ASD) φt = 0.90 (LRFD) (b) For fracture away from the connection: (Eq. C2-2) Tn = AnFu Ωt = 2.00 (ASD) φt = 0.75 (LRFD) where Tn = Nominal strength of member when loaded in tension Ag = Gross area of cross section An = Net area of cross section Fy = Yield point as specified in Section A7.1 Fu = Tensile strength as specified in Section A3.1 or A3.3.2

Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

(c)

9.

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For fracture at the connection: The nominal tensile strength shall also be limited by Sections E2.7, E3, and E4 for tension members using welded connections, bolted connections, and screw connections, respectively.

Section C3.1 Add the following footnote to the section title: *

The provisions of this Section do not consider torsional effects, such as those resulting from loads that do not pass through the shear center of the cross section. See Section D3 for the design of lateral bracing required to restrain lateral bending or twisting.

10. Section C3.1.2 Section C3.1.2, Lateral-Torsional Buckling, is revised to include two subsections: C3.1.2.1, Lateral-Torsional Buckling Strength for Open Cross Section Members, and C3.1.2.2, Lateral-Torsional Buckling Strength for Closed Box Members. Section C3.1.2.1 contains design provisions given in current Section C3.1.2 with revisions, and Section C3.1.2.2 is a new added section. The full text of both subsections is provided as follows: C3.1.2.1Lateral-Torsional Buckling Strength for Open Cross Section Members For laterally unbraced segments of singly-, doubly-, and point-symmetric sections∗ subject to lateral-torsional buckling, the nominal flexural strength, Mn, shall be calculated as follows: Mn = S c Fc (Eq. C3.1.2.1-1) Ωb = 1.67 (ASD) φb = 0.90 (LRFD) where Sc = Elastic section modulus of effective section calculated at a stress Fc relative to the extreme compression fiber Fc = Elastic or inelastic critical lateral-torsional buckling stress calculated as follows: For Fe ≥ 2.78Fy Fc = Fy (Eq. C3.1.2.1-2) For 2.78Fy > Fe > 0.56Fy Fc =

10  10Fy Fy 1 −  9 36Fe 

   

(Eq. C3.1.2.1-3)

For Fe ≤ 0.56Fy Fc = Fe (Eq.C3.1.2.1-4) where Fe = Elastic critical lateral-torsional buckling stress calculated according to (a) or (b) below: ∗

The provisions of this Section apply to I-, Z-, C- and other singly-symmetric section flexural members (not including multiple-web deck, U- and closed box-type members, and curved or arch members). The provisions of this Section do not apply to laterally unbraced compression flanges of otherwise laterally stable sections. Refer to C3.1.3 for C- and Zpurlins in which the tension flange is attached to sheathing.

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Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

(a) For singly-, doubly-, and point-symmetric sections: C r A σ ey σ t for bending about the symmetry axis. = bo Fe S

(Eq. C3.1.2.1-5)

f

Sf

= Elastic section modulus of full unreduced section relative to the extreme compression fiber For singly-symmetric sections, x-axis is the axis of symmetry oriented such that the shear center has a negative x-coordinate. For point-symmetric sections, use 0.5 Fe. X-axis of Z-sections is the centroidal axis perpendicular to the web. Alternatively, Fe can be calculated using the equation given in (b) for doublysymmetric I-sections or point-symmetric sections. For singly-symmetric sections bending about the centroidal axis perpendicular to the axis of symmetry: C Aσ   = s ex  j + C s j2 + ro2 (σ t /σ ex ) (Eq.C3.1.2.1-6) Fe C TF S f   Cs = +1 for moment causing compression on the shear center side of the centroid = -1 for moment causing tension on the shear center side of the centroid Cs σex

=

σey

=

σt A Cb

where: Mmax MA MB MC

E CTF

π2E

(K x L x / rx )2 π2E

(K y L y / ry ) 2

π 2 EC w  1  GJ +  (K t L t )2  Aro2  = Full unreduced cross-sectional area 12.5Mmax = 2.5Mmax + 3M A + 4M B + 3MC =

(Eq. C3.1.2.1-7)

(Eq. C3.1.2.1-8)

(Eq. C3.1.2.1-9)

(Eq. C3.1.2.1-10)

= Absolute value of maximum moment in unbraced segment = Absolute value of moment at quarter point of unbraced segment = Absolute value of moment at centerline of unbraced segment = Absolute value of moment at three-quarter point of unbraced segment Cb is permitted to be conservatively taken as unity for all cases. For cantilevers or overhangs where the free end is unbraced, Cb shall be taken as unity. For members subject to combined compressive axial load and bending moment (Section C5.2), Cb shall be taken as unity. = Modulus of elasticity = 0.6 - 0.4 (M1/M2) (Eq. C3.1.2.1-11) where M1 is the smaller and M2 the larger bending moment at the ends of the unbraced length in the plane of bending, and where M1/M2, the ratio of end moments, is positive when M1 and M2 have the same

Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

ro

11

sign (reverse curvature bending) and negative when they are of opposite sign (single curvature bending). When the bending moment at any point within an unbraced length is larger than that at both ends of this length, and for members subject to combined compressive axial load and bending moment (Section C5.2), CTF shall be taken as unity. = Polar radius of gyration of the cross section about the shear center

(Eq. C3.1.2.1-12) = rx2 + ry2 + x 2o rx, ry = Radii of gyration of the cross section about the centroidal principal axes G = Shear modulus Kx, Ky, Kt = Effective length factors for bending about the x- and y-axes, and for twisting Lx, Ly, Lt = Unbraced length of compression member for bending about the x- and y-axes, and for twisting xo = Distance from the shear center to the centroid along the principal x-axis, taken as negative J = St. Venant torsion constant of the cross section Cw = Torsional warping constant of the cross section j

=

1  x 3dA + xy 2 dA - x o   A 2I y  A

∫

∫

(Eq. C3.1.2.1-13)

(b) For I- or Z-sections bent about the centroidal axis perpendicular to the web (x-axis): In lieu of (a), the following equations may be used to calculate Fe: Fe

=

=

C b π 2 EdI yc S f L2 C b π 2 EdI yc 2Sf L2

for doubly-symmetric I-sections

(Eq. C3.1.2.1-14)

for point-symmetric Z-sections

(Eq. C3.1.2.1-15)

where d L Iyc

= Depth of section = Unbraced length of member = Moment of inertia of the compression portion of a section about the centroidal axis of the entire section parallel to the web, using the full unreduced section Other terms are defined in (a).

C3.1.2.2 Lateral-Torsional Buckling Strength for Closed Box Members For closed box members, the nominal flexural strength, Mn, shall be determined as follows: If the unbraced length of the member is less than or equal to Lu, the nominal flexural strength shall be determined by using Section C3.1.1. where 0.36Cb π EGJI y Lu = (Eq. C3.1.2.2-1) Fy S f If the lateral unbraced length of a member is larger than Lu, the nominal flexural strength shall be determined in accordance with C3.1.2.1, where the critical lateral buckling stress, Fe, is calculated as follows:

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Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

Fe

C π = b EGJIy LSf

(Eq. C3.1.2.2-2)

where L =Lateral unbraced length of member Iy =Moment of inertia of full unreduced section about its centroidal axis parallel to web J = Torsional Constant of box section Other variables are defined in Section C3.1.2.1. 11. Section C3.1.3 Replace the whole section as follows: C3.1.3 Beams Having One Flange Through-Fastened to Deck or Sheathing This section does not apply to a continuous beam for the region between inflection points adjacent to a support, or to a cantilever beam. The nominal flexural strength, Mn, of a C- or Z-section loaded in a plane parallel to the web, with the tension flange attached to deck or sheathing and with the compression flange laterally unbraced shall be calculated as follows: Mn =RSeFy (Eq. C3.1.3-1) Ωb =1.67 (ASD) φb =0.90 (LRFD) where R is obtained from Table C3.1.3-1 for simple span C- or Z-sections, and R = 0.60 for continuous span C-sections = 0.70 for continuous span Z-sections Se and Fy are defined in Section C3.1.1. The reduction factor, R, shall be limited to roof and wall systems meeting the following conditions: (1) Member depth less than 11.5 inches (292 mm) (2) Member flanges shall have edge stiffeners (3) 60 ≤ depth/thickness ≤ 170 (4) 2.8 ≤ depth/flange width ≤ 4.5 (5) 16 ≤ flat width/thickness of flange ≤ 43 (6) For continuous span systems, the lap length at each interior support in each direction (distance from center of support to end of lap) shall not be less than 1.5 d (7) Member span length shall be no greater than 33 feet (10 m) (8) For continuous span systems, the longest member span length shall not be more than 20% greater than the shortest span length (9) Both flanges shall be prevented from moving laterally at the supports (10) Roof or wall panels shall be steel sheets with 50 ksi (345 MPa) minimum yield strength, and a minimum of 0.018 in. (0.46 mm) base metal thickness, having a minimum rib depth of 1-1/4 in. (32 mm), spaced a maximum of 12 in. (305 mm) on centers and attached in a manner to effectively inhibit relative movement between the panel and purlin flange (11) Insulation shall be glass fiber blanket 0 to 6 inches (152mm) thick compressed between the member and panel in a manner consistent with the fastener being

Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

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used (12) Fastener type: minimum No. 12 self-drilling or self-tapping sheet metal screws or 3/16 in. (4.76 mm) rivets, having washers 1/2 in. (12.7 mm) diameter (13) Fasteners shall not be standoff type screws (14) Fasteners shall be spaced not greater than 12 in. (305 mm) on centers and placed near the center of the beam flange, and adjacent to the panel high rib (15) The design yield strength of the member shall not exceed 60 ksi (414 MPa) If variables fall outside any of the above stated limits, the user must perform full scale tests in accordance with Section F1 of the Specification, or apply a rational analysis procedure. In any case, the user is permitted to perform tests, in accordance with Section F1, as an alternate to the procedure described in this section. TABLE C3.1.3-1 Simple Span C- or Z-Section R Values Depth Range, in. (mm)

Profile

R

D ≤ 6.5 (165)

C or Z

0.70

6.5 (165) < d ≤ 8.5 (216)

C or Z

0.65

8.5 (216) < d ≤ 11.5 (292)

Z

0.50

8.5 (216) < d ≤ 11.5 (292)

C

0.40

For simple span members, R shall be reduced for the effects of compressed insulation between the sheeting and the member. The reduction shall be calculated by multiplying R from Table 3.1.3-1 by the following correction factor, r: when ti is in inches (Eq. C3.1.3-2) r =1.00 - 0.01 ti r =1.00 - 0.0004 ti when ti is in millimeters (Eq. C3.1.3-3) ti =thickness of uncompressed glass fiber blanket insulation 12. Section C3.1.4 • •

Delete “under gravity load,” and change “C3.1.2” to “C3.1.2.1” in the first paragraph. The “Base Test Method For Purlins Supporting a Standing Seam Roof System” is provided in Appendix A, in which the base test procedure for members subjected to uplift loads is included.

13. Section C3.1.5 The following is a new added section for the design of standing seam roof panel systems. The “Standard Procedures for Panel and Anchor Structural Tests” is provided in Appendix B of this Supplement. C3.1.5 Strength of Standing Seam Roof Panel Systems When results of tests on standing seam roof panel systems conducted according to ASTM E1592-95 are to be evaluated, the Standard Procedures for Panel and Anchor Structural Tests of Part VIII of the AISI Cold-Formed Steel Design Manual shall be followed. Strength under uplift loading shall be evaluated by this procedure. When the number of physical test assemblies is 3 or more, safety factors and resistance factors shall be determined in accordance with the procedures of Section

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Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

F1.1(b) with the following definition for the variables: β0 = Target reliability index = 2.0 for panel flexural limits = 2.5 for anchor limits Fm = Mean value of the fabrication factor = 1.0 Mm = Mean value of the material factor = 1.1 VM = Coefficient of variation of the material factor = 0.08 for anchor failure mode = 0.10 for other failure modes VF = Coefficient of variation of the fabrication factor = 0.05 VQ = Coefficient of variation of the load effect = 0.21 VP = Actual calculated coefficient of variation of the test results, without limit n = Number of anchors in the test assembly with same tributary area (for anchor failure), or number of panels with identical spans and loading to the failed span (for non-anchor failures) When the number of physical test assemblies is less than 3, a safety factor, Ω, of 2.0 and a resistance factor, φ, of 0.5 shall be used. 14. Section C3.2 This section is revised to include two subsections: C3.2.1, Shear Strength of Webs Without Holes, and C3.2.2, Shear Strength of C-Section Webs With Holes. Section C3.2.1 contains the design provisions given in current Section C3.2 (Note, the equation numbers in current Section C3.2 need to be revised to “(Eq. C3.2.1-” accordingly), and Section C3.2.2 is a new added section as provided in the following: C3.2.2 Shear Strength of C-Section Webs With Holes These provisions shall be applicable within the following limits: (1) d0 / h < 0.7 (2) h / t ≤ 200 (3) Holes centered at mid-depth of the web (4) Clear distance between holes ≥ 18 in. (457 mm) (5) Non-circular holes corner radii ≥ 2t (6) Non-circular holes, d0 ≤ 2.5 in. (64 mm) and b ≤ 4.5 in. (114 mm) (7) Circular hole diameters ≤ 6 in (152 mm) (8) d0 > 9/16 in. (14 mm) The nominal shear strength, Vn, determined by Section C3.2.1 shall be multiplied by qs: When c/t ≥ 54 qs = 1.0 (Eq. C3.2.2-1) When 5 ≤ c/t < 54 qs = c/(54t) (Eq. C3.2.2-3) where for circular holes (Eq. C3.2.2-4) c = h/2 - d0/2.83 for non-circular holes (Eq. C3.2.2-5) = h/2 - d0/2

Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

15

d0 = Depth of web hole b = Length of web hole h = Depth of flat portion of the web measured along the plane of the web 15. Section C3.4 This section is revised to include two subsections: C3.4.1, Web Crippling Strength of Webs Without Holes, and C3.4.2, Web Crippling Strength of C-Section Webs With Holes. Section C3.4.1 contains the design provisions given in the current section C3.4 with revisions as described below, and Section C3.4.2 is a new added section as provided subsequently. • Add subsection title “C3.4.1 Web Crippling Strength of Webs Without Holes” below the section title. • Revise section number “C3.4” referenced in current Section C3.4 to “C3.4.1”. • Revise Eqs. C3.4-1, C3.4-2, and C3.4-6 in current Section C3.4 to

• • • •

t2kC1C4C9Cθ[331 - 0.61(h/t)] [1 + 0.01(N/t)]

(Eq. C3.4.1-1)

t2kC1C4C9Cθ[217 - 0.28(h/t)] [1 + 0.01(N/t)] t2kC1C4C9Cθ[244 - 0.57(h/t)] [1 + 0.01(N/t)]

(Eq. C3.4.1-2) (Eq. C3.4.1-6)

Delete “C3 = 1.33-0.33k” and its corresponding equation number, replace with “C3 (Not used)”, and reduce the subsequent each equation number by 1. Delete the footnote on page V-53. Revise the definition for yield stress to “Fy = Yield point used in design of the web, see Section A7.1, ksi (MPa)”. Add the following new section C3.4.2: C3.4.2 Web Crippling Strength of C-Section Webs With Holes When a web hole is within the bearing length, a bearing stiffener shall be used. For beam webs with holes, the web crippling strength shall be computed by using Section C3.4.1 multiplied by the reduction factor, Rc, given in this section. These provisions shall be applicable within the following limits: (1) d0 / h ≤ 0.7 (2) h / t ≤ 200 (3) Hole centered at mid-depth of the web (4) Clear distance between holes ≥ 18 in. (457 mm) (5) Distance between the end of the member and the edge of the hole ≥ d (6) Non-circular holes, corner radii ≤ 2t. (7) Non-circular holes, d0 ≤ 2.5 in. (64 mm) and b ≤ 4.5 in. (114 mm) (8) Circular hole diameters ≤ 6 in. (152 mm) (9) d0 > 9/16 in. (14 mm) For using Equations C3.4.1-1 and C3.4.1-2 when a web hole is not within the bearing length: (Eq. C3.4.2-1) Rc = 1.01 − 0.325d 0 h + 0.083 x h ≤ 1.0 N ≥ 1 in. (25 mm) For using Equation C3.4.1-4 when any portion of a web hole is not within the bearing length:

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Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

Rc = 0.90 − 0.047 d 0 h + 0.053 x h ≤ 1.0 N ≥ 3 in. (76 mm) where b = Length of web hole d = Depth of cross section d0 = Depth of web hole

(Eq. C3.4.2-2)

h = Depth of flat portion of the web measured along the plane of the web x = Nearest distance between the web hole and the edge of bearing N = Bearing length 16. Section C3.5.1 Add the following two definitions before the definition for P: Ωb Ωw

= Factor of safety for bending (See Section C3.1.1) = Factor of safety for web crippling (See Section C3.4)

17. Section C4 Delete “(c) The slenderness ratio, KL/r, of all compression members preferably should not exceed 200, except that during construction only, KL/r preferably should not exceed 300.” This recommendation is moved to the Commentary (See Supplement to the Commentary for details). 18. Section C6.1 Change “0.070” to “0.0714” and “0.319” to “0.318” both in the upper and the lower limits for D/t. 19. Section C6.2 Eqs. C6.2-5 and C6.2-6 are revised as follows: Ae = A 0 + R(A − A 0 ) R = Fy 2Fe ≤ 1.0

(Eq. C6.2–5) (Eq. C6.2–6)

20. Section D3.2.1 •

• •

Replace the second and third sentences in the first paragraph with “If the top flanges of all purlins face in the same direction, anchorage of the restraint shall satisfy the requirements of Sections D3.2.1(a) and D3.2.1(b). If the top flanges of adjacent lines of purlins face in opposite directions, a restraint system shall be provided to resist the down-slope component of the total gravity load.” In the third paragraph, change “braced Z-section” to “purlin”. Replace the section, (a) C-Sections, with the following:

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17

(a) C-Sections For roof systems using C-sections for purlins with all compression flanges facing in the same direction, a system possessing restraint force, PL, in addition to resisting other loading, shall be provided: (Eq. D.3.2.1-1) PL = (0.05αcosθ - sinθ)W where W = Total vertical load (nominal load for ASD, factored load for LRFD) supported by all purlin lines being restrained. Where more than one brace is used at a purlin line, the restraint force PL shall be divided equally between all braces. α = +1 for purlin facing upward direction, and -1 for purlin facing down slope direction. θ = Angle between the vertical and the plane of the web of the C-section, degrees. A positive value for the force, PL, means that restraint is required to prevent movement of the purlin flanges in the upward roof slope direction, and a negative value means that restraint is required to prevent movement of purlin flanges in the downward slope direction. • • •

Increase the equation sequence number by 1 for all the equations in the section, (b) Z-Sections. Add “cosθ” to the first term in the square brackets of all the equations in the section, (b) Z-Sections. Add “vertical” after “Total” in the definition for W.

21. Section D3.3 Delete Section D3.3. 22. Section E2.6 The whole section is revised as follows: The nominal shear strength, Pn, of spot welds shall be determined as follows: When t is in inches and Pn is in kips: For 0.01 in. ≤ t < 0.14 in.: Pn = 144t 1.47 For 0.14 in. ≤ t ≤ 0.18 in.: Pn = 43.4t + 1.93 When t is in millimeters and Pn is in kN:

(Eq. E2.6-1) (Eq. E2.6-2)

For 0.25 mm ≤ t < 3.56 mm: Pn = 5.51t 1.47 For 3.56 mm ≤ t ≤ 4.57 mm: Pn = 7.6t + 8.57 where t = Thickness of thinnest outside sheet. Ω = 2.50 (ASD) φ = 0.65 (LRFD)

(Eq. E2.6-3) (Eq. E2.6-4)

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Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

23. Section E2.7 Add the following new section: E2.7 Shear Lag Effect in Welded Connections of Members Other Than Flat Sheets The nominal tensile strength of a welded member shall be determined in accordance with Section C2. For fracture and/or yielding in the effective net section of the connected part, the nominal tensile strength, Pn, shall be determined as follows: (Eq. E2.7-1) Pn = AeFu Ω = 2.50 φ = 0.60 Fu = Tensile strength of the connected part as specified in Section A3.1 or A3.3.2 Ae = AU, effective net area with U defined as follows: When the load is transmitted only by transverse welds: A = Area of directly connected elements U = 1.0 When the load is transmitted only by longitudinal welds or by longitudinal welds in combination with transverse welds: A = Gross area of member, Ag U = 1.0 for members when the load is transmitted directly to all of the cross sectional elements. Otherwise the reduction coefficient U is determined as follows: (a) For angle members: U = 1.0 - 1.20 x L < 0.9 but U shall not be less than 0.4. (b) For channel members

(Eq. E2.7-2)

U = 1.0 - 0.36 x L < 0.9 but U shall not be less than 0.5.

(Eq. E2.7-3)

x = Distance from shear plane to centroid of the cross section L = Length of longitudinal welds 24. Section E3.2 Replace the whole section with the following: E3.2 Shear Lag Effect in Bolted Connections The nominal tensile strength of a bolted member shall be determined in accordance with Section C2. For fracture and/or yielding in the effective net section of the connected part, the nominal tensile strength, Pn, shall be determined as follows: (1) For flat sheet connections not having staggered hole patterns: Pn = AnFt (Eq. E3.2-1) (a) When washers are provided under both the bolt head and the nut: Ft = (1.0 - 0.9r + 3rd/s) Fu < Fu For double shear: Ω = 2.0 (ASD) φ = 0.65 (LRFD)

(Eq. E3.2-2)

Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

For single shear: Ω = 2.22 (ASD) φ = 0.55 (LRFD) (b) When either washers are not provided under the bolt head and the nut, or only one washer is provided under either the bolt head or the nut: (Eq. E3.2-3) Ft = (1.0 - r + 2.5rd/s) Fu < Fu Ω = 2.22 (ASD) φ = 0.65 (LRFD) where An = Net area of the connected part r

= Force transmitted by the bolt or bolts at the section considered, divided by the tension force in the member at that section. If r is less than 0.2, it shall be permitted to be taken as equal to zero. s = Spacing of bolts perpendicular to line of stress; or gross width of sheet for a single line of bolts. Fu = Tensile strength of the connected part as specified in Section A3.1 or A3.3.2 d is defined in Section E3.1 (2) For flat sheet connections having staggered hole patterns: Pn = AnFt (Eq. E3.2-4) Ω = 2.22 φ = 0.65 where Ft is determined as follows: (a) For connections when washers are provided under both the bolt head and the nut: (Eq. E3.2-5) Ft = (1.0 - 0.9r + 3rd/s) Fu ≤ Fu (b) For connections when no washers are provided under the bolt head and the nut, or only one washer is provided under either the bolt head or the nut: (Eq. E3.2-6) Ft = (1.0 - r + 2.5rd/s) Fu ≤ Fu (Eq. E3.2-7) An = 0.90 [Ag - nbdht + (∑s′2/4g)t] Ag = Gross area of member s = Sheet width divided by the number of bolt holes in the cross section being analyzed (when evaluating Ft) s′ = Longitudinal center-to-center spacing of any two consecutive holes g = Transverse center-to-center spacing between fastener gage lines nb = Number of bolt holes in the cross section being analyzed dh = Diameter of a standard hole t is defined in Section E3.1. (3) For other than flat sheet: (Eq.E3.2-8) Pn = AeFu Ω = 2.22 φ = 0.65 where Fu = Tensile strength of the connected part as specified in Section A3.1 or A3.3.2

19

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Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

Ae = AnU, effective net area with U defined as follows: U = 1.0 for members when the load is transmitted directly to all of the crosssectional elements. Otherwise, the reduction coefficient U is determined as follows: (a) For angle members having two or more bolts in the line of force (Eq. E3.2-9) U = 1.0 - 1.20 x L < 0.9 but U shall not be less than 0.4. (b) For Channel members having two or more bolts in the line of force U = 1.0 - 0.36 x L < 0.9 but U shall not be less than 0.5.

(Eq. E3.2-10)

x = Distance from shear plane to centroid of the cross section L = Length of the connection 25. Section E3.3 •

Replace the first and the second paragraphs with the following: When deformation around the bolt holes is not a design consideration, the nominal bearing strength, Pn , and applicable Ω and φ shall be as given in Tables E3.3–1 and E3.3–2 for the applicable thickness and Fu /Fsy ratio of the connected part and the type of joint used in the connection. When deformation around the bolt holes is a design consideration, the nominal bearing strength shall also be limited by the following values: Pn = (4.64 t + 1.53)dtFu (with t in inches) (Eq. E3.3-1) For SI Units: Pn = (0.183 t + 1.53)dtFu (with t in mm) (Eq. E3.3-2) And Ω = 2.22 φ = 0.65 The symbols Ω, φ, d, Fu, e and t in Tables E3.3-1 and E3.3-2 are defined in Sections E3.1 and E.3.2. For conditions not shown, the design bearing strength of bolted connections shall be determined by tests.

•

Change the lower limit of thickness, t, in Tables E3.3-1 and E3.3-2 from “0.024” in. to “0.036” in. and the corresponding metric units from “0.61” mm to “0.91” mm.

26. Section E5 The section title is changed to “E5, Rupture”, and three subsections are included: E5.1, Shear Rupture; E5.2, Tension Rupture; and E5.3, Block Shear Rupture. Subsection E5.1 contains the design provisions given in current Section E5, and Subsections E5.2, and E5.3 are the new added sections. Changes to current Section E5 and the content of the new sections are provided as follows: • Change the variable in the equation for Awc from “dwc” to “hwc” and revise the definitions to “hwc = Coped flat web depth” and “Fu = Tensile strength of the connected part as specified in Section A3.1 or A3.3.2”. • Add the following two new sections:

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21

E5.2 Tension Rupture The nominal tensile rupture strength along a path in the affected elements of connected members shall be determined by Section E2.7 or E3.2 for welded or bolted connections, respectively. E5.3 Block Shear Rupture The nominal block shear rupture design strength, Rn, shall be determined as follows: (a) When FuAnt ≥ 0.6FuAnv Rn = 0.6FyAgv + FuAnt (Eq. E5.3-1) (b) When FuAnt < 0.6FuAnv Rn = 0.6FuAnv + FyAgt (Eq. E5.3-2) For bolted connections: Ω =2.22 φ =0.65 For welded connections: Ω =2.50 φ =0.60 where Agv= Gross area subject to shear Agt = Gross area subject to tension Anv= Net area subject to shear Ant = Net area subject to tension 27. Section E6.1 Replace the whole section as follows: Proper provisions shall be made to transfer bearing forces from steel components covered by the Specification to adjacent structural components made of other materials. 28. Section F1 •

Add the following entry to Table F1 on page V-99 as the last entry: Type of Component

Mm

VM

Fm

VF

1.00

0.10

1.00

0.05

………… Structural Members Not Listed Above

•

Add the following entry to Table F1 on page V-100 as the last entry:

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Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1

Type of Component

Mm

VM

Fm

VF

1.10

0.10

1.00

0.15

………… Connections Not Listed Above

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APPENDIX A:

BASE TEST METHOD FOR PURLINS SUPPORTING A STANDING SEAM ROOF SYSTEM 1. Scope 1.1 The purpose of this test is to obtain the reduction factor to be used in determining the nominal flexural strength of a purlin supporting a standing seam roof system. The reduction factor reflects the ability of a particular standing seam roof system to provide lateral and rotational support to the purlins to which it is attached. This applies to discrete lateral and torsional bracing when the sheeted flange of the purlin is the compression flange, as in gravity loading cases, and when the unsheeted flange is the compression flange, as in wind uplift cases. 1.2 This test method applies to an assembly consisting of the standing seam panel, purlin, and attachment devices used in the system being tested. The test specimen boundary conditions described in Section 6.6 apply only to standing seam roof systems for which the roof deck is positively anchored to the supporting structural system at one or more purlin or eave member lines. 1.3 Due to the many different types and construction of standing seam roof systems and their attachments, it is not practical to develop a generic method to predict the interaction of a particular standing seam roof system and supporting structure. Therefore, the amount of resisting moment which the supporting purlins can achieve can vary from the fully braced condition to the unbraced condition for a given system. 1.4 This test method provides the designer with a means of establishing a nominal flexural strength reduction factor for purlins in a simple span or continuous span, multiple purlin line, supporting a standing seam roof system, from the results of tests on a single-span, two-purlin line, sample of the system. The validity of this test method has been established by a research program at Virginia Polytechnic Institute and State University and documented in References 1 through 6. 2. Applicable Documents 2.1 ASTM Standards: A370 - Standard Test Methods and Definitions for Mechanical Testing of Steel Products 2.2 AISI Specification for the Design of Cold-Formed Steel Structural Members, 1996 Edition. 3. Terminology 3.1 ASTM Definition Standards: E6 - Definitions of Terms Relating to Methods of Mechanical Testing. E380 - Practice for Use of the International System of Units (SI). 3.2 Description of terms specific to this standard: fixed clip - a hold down clip which does not allow the roof panel to move independently of the roof substructure insulation - glass fiber blanket or rigid board lateral - a direction normal to the span of the purlins in the plane of the roof sheets thermal block - strips of rigid insulation located directly over the purlin between clips negative moment - a moment which causes tension in the purlin flange attached to the clips and

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24

standing seam panels pan type standing seam roof - a "U" shaped panel which has vertical sides positive moment - a moment which causes compression in the purlin flange attached to the clips and standing seam panels rib type standing seam roof - a panel which has ribs with sloping sides and forms a trapezoidal shaped void at the side lap sliding clip - a hold down clip which allows the roof panel to move independently of the roof substructure standing seam roof system - a roof system in which the side laps between the roof panels are arranged in a vertical position above the roof line. The roof panel system is secured to the purlins by means of concealed hold down clips that are attached to the purlins with mechanical fasteners 3.3 Symbols: b d B Fy Fyt L Mn

= = = = = = =

Flange width of the purlin Depth of the purlin Purlin spacing Design yield strength Measured yield strength of tested purlin Span of the purlins tested, center to center of the supports Nominal flexural strength of a fully constrained beam, SeFy

Mnt min = Average flexural strength of the thinnest sections tested Mnt max = Average flexural strength of the thickest sections tested Mnt

= Flexural strength of a tested purlin, SetFyt

Mts pd pts PL Rt R R t min

= = = = = = =

Failure moment for the single span purlins tested, wtsL2/8 Weight of the specimen (force/area) Failure load (force/area) of the single span system tested Lateral anchorage force in accordance with Section D3.2.1 of the AISI Specification Modification factor from test, Mts/Mnt Reduction factor computed for nominal purlin properties Mean minus one standard deviation of the modification factors of the three thinnest

purlins tested R t max = Mean minus one standard deviation of the modification factors of the three thickest s Se Set t wts

purlins tested = Tributary width of the purlins tested = Section modulus of the effective section = Section modulus of the effective section of the tested member using measured dimensions and the measured yield strength = Purlin thickness = Failure load (force/length) of the single span purlins tested

4. Significance 4.1 This test method provides the requirements for evaluating the resisting moment for cold-formed Cand Z-sections used with standing seam roof systems. This procedure is referred to as the “Base Test Method”. The method is the result of extensive testing of various combinations of purlins, standing seam panels, and fastening devices. The tests were conducted over several years, benefiting from the

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experience provided by technical and industry experts. This procedure utilizes the results obtained from single span tests to predict the strength of multi-span conditions. 4.2 The Base Test Method shall be permitted to be used to evaluate the nominal flexural strength of Cand Z-sections of multi-span, multiple purlin line, standing seam systems, with or without discrete intermediate braces. 4.3 The Base Test Method is applicable to both “rib” or “pan” type standing seam roof panels with “sliding” or “fixed” type clips. 4.4 The Base Test Method shall be conducted using standing seam roof panels, clips, fasteners, insulation, thermal blocks, discrete braces, and purlins as used in the actual standing seam roof system except as noted in Section 4.5. 4.5 Tests conducted with insulation are applicable to identical systems with thinner or no insulation. 5. Apparatus 5.1 A test chamber capable of supporting a positive or negative internal pressure differential is necessary. A rectangular frame shall be constructed of any material with sufficient strength and rigidity to provide the desired pressure differential without collapse. A typical test chamber is shown on Figure 1. Other chamber orientations shall be permitted.

STANDING SEAM PANELS

L3x3x1/4

SUPPORT BEAM L1x1x1/8

PURLINS

AL

NT

ZO RI

HO

LO

NG

ITU

VERTICAL

DI

NA

L

DEFLECTION DIRECTIONS

Figure 1 – Test Chamber 5.2 The length of the chamber shall be determined by the maximum length of the secondary members

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as required by Section 7.2. The width of the chamber shall be determined by the maximum panel length as required by Section 6.9. Allowance shall be made in the interior chamber dimensions to accommodate structural supports for the secondary members and sufficient clearance on all sides to prevent interference of the chamber wall with the test specimen as it deflects. 5.3 The height of the chamber shall be sufficient to permit assembly of the specimen and to insure adequate clearance at the maximum deflection of the specimen. 5.4 The chamber shall be sealed in a manner to prevent air leakage. All load carrying elements of the specimen or its supports shall transfer the load to the frame support; the specimen, including intermediate brace, shall not be attached to the chamber in any manner that would impede the deflection of the specimen. 5.5 The test chamber shall be sealed against air leakage by applying 6 mil (0.15 mm) maximum thickness polyethylene sheets, large enough to accommodate the system configuration and deflections. The polyethylene shall be located on the high pressure side of the panel with sufficient folds so as not to inhibit the spread of panel ribs under load. Edges of the polyethylene sheets shall be sealed against air leakage with tape or other suitable methods. Polyethylene sheets around the perimeter of the specimen shall be draped so as not to impede deflection or deformation of the specimen. 5.6 When a specimen smaller than the test chamber is tested, other panels and structure shall be installed to complete the coverage of the chamber opening. No attachment shall be made between the test specimen and this supplemental coverage. 5.7 An air pump is necessary to create the pressure differential in the chamber. The pump shall be of sufficient capacity to reach the expected test values required by the applicable specifications. 5.8 The type of air pump being used will determine the method of control. This control shall be able to regulate the pressure differential in the chamber to ± 1 psf (0.05 kPa). This can be accomplished by (a) a variable speed motor on the pump, (b) valving on the pump, or (c) variable size orifices on the chamber. It shall be permitted to use multiple pumps where very large chambers are being used. One pump connection to the chamber is satisfactory. 5.9 A minimum of two pressure differential measuring devices shall be monitored throughout the duration of the test. These devices shall be capable of measuring the pressure differential to ± 1 psf (0.05 kPa). 6. Test Specimens 6.1 Test purlins shall be supported at each end by a steel beam. The beams shall be simply supported and one of the frame end beams shall be sufficiently free to translate laterally to relieve any longitudinal catenary forces in the specimen. Purlins shall be connected to the supporting beams as recommended in the field erection drawings. Figure 1 shows the directional axes that are referred to in this test procedure. 6.2 Panel supporting clips, fasteners, and panels shall be installed as recommended in the field erection drawings. 6.3 Means of providing restraint of purlins at the support shall be as required for use in actual field application, and shall be installed as recommended on the field erection drawings.

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6.4 The purlins shall be arranged either with their flanges facing in the same direction or with their flanges opposed. If the test is performed with the purlins opposed, and they are field installed with their flanges facing in the same direction, a diaphragm test must be conducted in accordance with Section 8.7. 6.5 For tests including intermediate discrete point braces, the braces used in the test shall be installed in such a manner so as not to impede the vertical deflection of the specimen. 6.6 A 1 in. x 1 in. (25 mm x 25 mm) continuous angle with a maximum thickness of 1/8 in. (3 mm) or a member of compatible stiffness shall be attached to the underside at each end of the panels to prevent separation of the panels at the ends of the seam. Fasteners shall be placed on both sides of each major rib. If the specimen is arranged with the purlin flanges facing in the same direction, a 3 in. x 3 in. (76 mm x 76 mm) continuous angle with a maximum thickness of 1/4 in. (6 mm) or a member of compatible stiffness shall be permitted to be substituted for the 1 in. x 1 in. (25 mm x 25 mm) angle at the end of the panel, corresponding to the eave of the building using the standard panel to eave fastening system. (See Figure 1) 6.7 All transverse panel ends shall be left free to displace vertically under load. When the 3 in. x 3 in. (76 mm x 76 mm) eave angle is used when the purlin flanges face in the same direction, it shall be permitted to be restrained against horizontal deflection at its ends as shown in Figure 1, providing vertical deflection is left unrestrained. 6.8 Panel joints shall not be taped and no tape shall be used to restrict panel movement. 6.9 Panel length to be used in the test shall be, as a minimum, that length which provides full engagement of the panel to purlin clip and attachment of the 1 in. x 1 in. (25 mm x 25 mm) angle at the panel ends; but a length not greater than that required to achieve zero slope of the panel at the purlin support. 6.10 The spacing of purlins being tested shall not exceed the spacing typically used with the roof system. Results from this test shall be permitted to be used in designing purlins of the same profile that are spaced closer together than the spacing used in the tests. 7. Test Procedure 7.1 A test series shall be conducted for each purlin profile, specified steel grade, and each panel system. Any variation in the characteristics or dimensions of panel or clip constitute a change in panel system. The thickness of insulation used in the test is discussed in Section 4.5. Any change in purlin shape or dimension other than thickness constitutes a change in profile. However, the lip dimension shall be permitted to vary with section thickness consistent with the member design and not constitute a change in profile. 7.2 No fewer than six tests shall be run for each combination of purlin profile and panel system. Three tests shall be conducted with the thinnest purlin of the profile and three tests shall be conducted with the thickest purlin of the profile. All tests shall be conducted using the same purlin span which shall be the same or greater than the span used in actual field conditions. 7.3 The physical and material properties shall be determined in accordance with ASTM A370 using coupons taken from the web area of the failed purlin. Coupons shall not be taken from areas where coldworking stresses could affect the results. 7.4 For gravity loading, a pressure differential load shall be applied to the system to produce a positive

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moment in the system. A positive moment is defined as one which causes compression in the purlin flange attached to the clips and standing seam panels. For uplift loading, a pressure differential load shall be applied to the system to produce a negative moment in the system. A negative moment is defined as one which causes tension in the purlin flange attached to the clips and standing seam panels. 7.5 An initial load equal to 5 psf (0.25 kPa) differential pressure in the direction of the test load shall be applied and removed to set the zero readings before actual system loading begins. 7.6 The system shall be loaded to failure and the mode of failure noted. Failure is the point at which the specimen will accept no further loading. The pressure differential at which the system fails shall be recorded as the failure load of the specimen. When the test must be stopped due to a flexural failure of the panel or web crippling of the purlin, it shall be permitted to exclude the test from the test program. 7.7 Vertical deflection measurements shall be taken at the mid-span of both purlins. The deck deflection in the horizontal direction shall be measured at the seam joint nearest the center of the test specimen. 7.8 Deflections and pressures shall be recorded at pressure intervals equal to a maximum of 20 percent of the anticipated failure load. 8. Test Evaluation 8.1 The single span failure load is obtained from the Base Test where a uniform load is applied until failure occurs. The computation of the failure load, wts, is dependent on the purlin orientation for Zpurlins and on the nature of the load as follows: For Z-purlins tested for gravity loading, with flanges facing the same direction and with the top flanges of the purlins not restrained by anchorage to a point external to the panel/purlin system: d w ts = (p ts + p d )s + 2PL    B where   b1.5 (p + p )s PL = 0.041 d  d 0.90 t 0.60  ts   For Z-purlins tested for gravity loading with flanges opposed and for C-sections tested for gravity loading: w ts = (p ts + p d )s

For Z-purlins or C-sections tested for uplift loading: w ts = (p ts − p d )s

The expression 2PL(d/B) takes into account the effect of the overturning moment on the system due to the anchorage forces, as defined in Section D3.2.1 of the AISI Specification, applied at the top flange of the purlin by the panel and resisted at the bottom flange of the purlin at the support. The expression 2PL(d/B) is to be applied only to Z-sections under gravity loading when the purlin flanges are facing in the same direction, but shall not be included in those systems where discrete point braces are used when

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the braces are restrained from lateral movement. 8.2 From the single span failure load, wts, the maximum single span failure moment Mts is calculated as: Mts = wts L2 / 8 8.3 The single span base test moment is the maximum moment the system can resist with the purlin size used in the test. The maximum allowable moment of a roof system purlin, simple span or continuous, is limited by the results of this test. The gravity load results apply for positive moment regions in the span and uplift load results apply for negative moment regions in the span. 8.4 Using Section C3.1.1(a) of the AISI Specification, the flexural strength of each tested purlin, Mnt, of a fully constrained beam is calculated as: Mnt = Set × Fyt where Set is the section modulus of the effective section calculated using the measured cross-sectional dimensions and measured yield strength and Fyt is the measured yield strength obtained in accordance with Section 7.3. 8.5 The modification factor, Rt, is calculated for each purlin tested as: Rt = Mts / Mnt 8.6 For purlins of the same profile, specified steel grade, and panel system as tested, the reduction factor shall be determined from the following equation:  Rt max − R t min R=  M nt − M nt min max 

 M −M nt min + R t min ≤1.0  n 

(

)

where R t min = Mean minus one standard deviation of the modification factors of the three thinnest purlins tested, calculated in accordance with Section 8.5. This value may be greater than 1.0 R t max = Mean minus one standard deviation of the modification factors of the three thickest purlins tested, calculated in accordance with Section 8.5. This value may be greater than 1.0 = Nominal flexural strength of section for which R is being evaluated (SeFy) Mn Mnt min = Average flexural strength of the thinnest section tested, calculated in accordance with Section 8.4 Mnt max = Average flexural strength of the thickest section tested, calculated in accordance with Section 8.4 8.7 If the test is performed with the purlins opposed or with an eave member at one or more edges, the diaphragm strength and stiffness of the panel system must be tested unless the purlins are also opposed

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in actual field usage. The anchorage forces for the system braced in the manner tested shall be calculated in accordance with Section D3.2.1 of the AISI Specification. The diaphragm strength of the panel system must be equal to or greater than the calculated brace force at the failure load of the purlin. The stiffness of the diaphragm must be such that the deflection of the diaphragm is equal to or less than the purlin span divided by 360 when subjected to the calculated brace force at the failure load of the purlin. 9. Test Report 9.1 Documentation - The report shall include who performed the test and a brief description of the system being tested. 9.2 The documentation shall include test details with a drawing showing the test fixture and indicating the components and their locations. A written description of the test setup detailing the basic concept, loadings, measurements, and assembly shall be included. 9.3 The report shall include a drawing showing the actual geometry of all specimens including material specifications and test results defining the actual material properties - material thickness, yield strength, tensile strength, and percent elongation. 9.4 The report shall include the test designation, loading increments, displacements, mode of failure, failure load, and specimen included for each test. 9.5 The report shall include a description summarizing the test program results to include specimen type, span, failure moments for the test series, and the supporting calculations. References (1) S. Brooks and T. Murray, “Evaluation of the Base Test Method for Predicting the Flexural trength of Standing Seam Roof Systems Under Gravity Loading,” MBMA Project 403, VPI Report No. CE/VPIST89/07, Metal Building Manufacturers Association, 1300 Sumner Ave., Cleveland, Ohio 44115, July 1989, Revised November 1990. (2) S. Brooks and T. Murray, "A Method for Determining the Strength of Z- and C-Purlin Supported Standing Seam Roof Systems", Proceedings of the Tenth International Specialty Conference on ColdFormed Steel Structures, St. Louis, October 23-24, 1990, pp. 421-440. (3) L. Rayburn and T. Murray, “Base Test Method for Gravity Loaded Standing Seam Roof Systems,” MBMA Project 502, VPI Report No. CE/VPI-ST90/07, Metal Building Manufacturers Association, 1300 Sumner Ave., Cleveland, Ohio 44115, December 1990. (4) T. Murray and B. Anderson, “Base Test Method for Standing Seam Roof Systems Subject to Uplift Loading - Phase I,” MBMA Project 501, VPI Report No. CE/VPI-ST90/06, Metal Building Manufacturers Association, 1300 Sumner Ave., Cleveland, Ohio 44115, December 1990, Revised December 1991. (5) T. Murray and A. Pugh, “Base Test Method for Standing Seam Roof Systems Subject to Uplift Loading - Phase II,” MBMA Project 602, VPI Report No. CE/VPI-ST91/17, Metal Building Manufacturers Association, 1300 Sumner Ave., Cleveland, Ohio 44115, December 1991. (6) T. Murray, “Base Test Method for Uplift Loading - Final Report,” MBMA Project 501, 602 and 702, VPI Report No. CE/VPI-ST-97/10, Metal Building Manufacturers Association, 1300 Sumner Ave., Cleveland, Ohio 44115, November 1997.

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APPENDIX B:

STANDARD PROCEDURES FOR PANEL AND ANCHOR STRUCTURAL TESTS 1. Scope This procedure extends and provides methodology for interpretation of results of tests performed according to ASTM E1592-95. 2. Referenced Documents 2.1 ASTM Standards: E1592-95, Standard Test Method for Structural Performance of Sheet Metal Roof and Siding Systems by Uniform Static Air Pressure Difference A370-97 Standard Test Methods and Definitions for Mechanical Testing of Steel Products 2.2 AISI Standards: Specification for the Design of Cold Formed Steel Structural Members, 1996 Edition. Base Test Method for Purlins Supporting a Standing Seam Roof System, AISI Cold Formed Steel Design Manual, Chapter VIII 3. Terminology 3.1 Refer to Section 3, ASTM E1592-95. 3.2 Additional or Modified Terminology 3.2.1 clip, a single or multiple element device that frequently attaches to one edge of a panel and is fastened to the secondary structural members with one or more screws. 3.2.2 field, the area that is not included in high pressure edge strip conditions. For purposes of the test, a field condition is modeled when the pan distortions are independent of end and edge restraint. 3.2.3 pan, the relatively flat portion of a panel between ribs. 3.2.4 tributary area, the area directly supported by the structural member between adjacent supports. 3.2.5 trim, the sheet metal used in the finish of a building especially around openings, and at the intersection of surfaces such as roof and walls. 3.2.6 ultimate load, the difference in static air pressure at which failure of the specimen occurs, expressed in load per unit area, and is further defined as the point where the panel system cannot sustain additional loading. 3.2.7 unlatching failure, disengagement of a panel seam or anchor that occurs in an unloaded assembly due to permanent set or distortion that occurred when the assembly was loaded. This permanent set is not always detectable from readings taken normal to the panel. It is deemed to be a serviceability failure until a strength failure occurs, as defined in 3.2.6, ultimate load. 4. Summary of the Test Method 4.1

Refer to the requirements of Section 4, ASTM E1592-95.

5. Significance and End Use 5.1 Refer to the requirements of Section 5, ASTM E1592-95. 5.2 The end use of the procedure is the determination of allowable load carrying capacity of panels and/or their anchors under gravity or suction loading for use in a design procedure. 6.

Test Apparatus 6.1

Refer to the requirements of Section 6, ASTM E1592-95.

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7.

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Safety Precautions 7.1

8.

Refer to the requirements of Section 7, ASTM E1592-95.

Test Specimens 8.1 Refer to the requirements of Section 8, ASTM E1 592-95. 8.2 Specimen Width - Edge seals shall not contain attachments that restrict deflection of the test panel in the field in any way. No additional structural attachments that would resist deflection of the field of the test panels are permitted. 8.2.1 The test panel ribs shall be installed parallel to the long side of the test chamber. 8.3 Number of Tests 8.3.1 Tests shall use minimum thickness of support members (secondary structures) and maximum panel span. If results are to be interpolated for other values, the other extremes must be tested in order to justify an interpolation procedure. 8.3.2 Tests shall be conducted to evaluate the field condition.

9.

Calibration 9.1

Refer to the requirements of Section 9, ASTM E1592-95.

10. Procedures 10.1 Refer to the requirements of Section 10, ASTM E1592-95 11. Test Evaluation 11.1 Safety factors and resistance factors shall be determined in accordance with the procedures in Chapter F and Section C3.1.5 of the AISI Specification for the Design of Cold Formed Steel Structural Members. 11.2 If a separate test series is performed to evaluate edge conditions and the results exceed the field case by greater than one standard deviation, a separate design allowable is permitted to be established for edge conditions. 11.3 A qualified design professional shall analyze deflections and permanent set data to assure that deflections and permanent set are acceptable at service loads. 12. Test Report 12.1 Refer to the requirements of Section 11, ASTM E1592-95. 12.2 Report the resistance factor and/or the safety factor based on the Section C3.1.5 for the test results. If the factor of safety is defined, report the allowable uniform design strength of the panel system. If the allowable design strengths of the panel and anchors are determined separately, they shall be reported separately. 12.3 If intermediate values are to be calculated for different spacings of anchors or secondary structures, the basis of the interpolation shall be stated in the report. If the failure modes are different on any two tests, interpolation between these two tests is not permitted. 12.4 The design professional shall include in the report the observation as to the acceptability of deflections and permanent set data at service loads.

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COMMENTARY ON THE STANDARD PROCEDURES FOR PANEL AND ANCHOR STRUCTURAL TESTS 1.

Scope The scope of the Procedure is for testing single skin panel systems. The procedure is based on ASTM E1592-95 with specific additions to define the required safety factors for a design procedure. Edge strip detail confirmation is permitted by the test method.

2.

Reference Documents The previously developed standards, ASTM E1592-95 and the AISI Base Test Method have been used in the development of this procedure.

3.

Terminology To promote accuracy and understanding, frequently used terms need mutual understanding. This list includes the terms from ASTM E1592-95 with additions and modifications.

5.

Significance and End Use Currently, there are several organizations that have test procedures to determine product performance, but the procedures are limited to one product configuration and do not have provisions to provide the basis for a complete design procedure covering the evaluation of a safety factor for a range of product configurations. Therefore, this new Standard Procedure was developed.

6.

Test Apparatus The apparatus defined in this section is specific enough to accomplish the purpose, yet broad enough to allow many facilities to perform tests. The size of the specimen is the most important criteria. Whether or not the apparatus consists of two sections with the specimen in between is not a major issue. Measurement of rib spread has dubious value except when seam disengagement is the failure mechanism. In that case, measurements tend to substantiate the failure mechanism.

7.

Safety Precautions In addition to other precautions, care must be exercised in taking the deflection readings required in this procedure.

8.

Test Specimens The size of a test specimen has been found to be an important element in demonstrating product performance. Minimum sizes are defined, but larger sizes are allowed. It is understood that many products are offered to the market that have insufficient usage to justify a large test program yet proof of performance to some degree is required. The procedure is developed to allow a single test with a corresponding penalty due to the reduced degree of demonstrated reliability with only a single test. The procedures of Section F provide for the reward/penalty relationship developed with increasing number of tests and the associated coefficient of variation. Minimum specimen size is as required in ASTM E1592-95. The minimum specimen length of 24 ft. (7.3 m) for the condition of constraint at both ends is consistent with the requirements of Factory Mutual Procedure 4471 (1995). However, in the FM tests, panels are fastened down at all edges and it is termed a field test. The details of the FM test do not meet the ASTM E1592-95 tests in many conditions. A purlin space of 5 ft. (1.5 m) requires 5 spans with both ends restrained. If one end is left free, the FM test will meet E-1592-95. The application is also different in many cases because typically FM tests are run

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with both ends restrained and this is used as a field test. Different results may be obtained when using the three variations of panel end restraints in the test procedure that are allowed by E 1592-95. When totaling the number (n) of anchors tested for evaluation of Cp under the AISI Specification Section C3.1.5, it is permissible to include all fasteners with the same tributary area as that associated with a failed anchor instead of merely totaling the number of physical tests run on a complete assembly. When totaling the number (n) of panels tested for evaluation of Cp under the AISI Specification Section C3.1.5, it is permissible to include all panels with the same tributary area as that associated with a failed panel instead of merely totaling the number of physical tests run on a complete assembly Consideration is given to the minimum spacings and material thicknesses. If allowables developed under this procedure are intended to be used in a design procedure that encompasses different secondary structural support spacings or thinner sections for anchors to attach to, the extremes must be tested in order for interpolation to be valid. This precedent is established in the AISI Base Test Method for validating the performance of purlins braced by standing seam roof panels. 10. Procedures The procedures for loading the specimen, while not complicated, need to be defined consistent with other existing and recognized standards. A significant difference between this procedure and the AISI Base Test Method is the return to zero load after each load increment. 11. Test Evaluation See Section C3.1.5 of the Commentary for the AISI Specification. 12. Test Report The definition of items to be included in the report includes the typical list of failure loads and plots of load versus deformation. Of paramount importance is the calculation of the resistance factor and safety factor of design strength or allowable design strength for panels and anchors. This procedure is an addition to those required in ASTM E1592-95. If interpolation is to be a part of the resulting design process, then appropriate interpolation procedure should be set forth in the report. REFERENCES: Factory Mutual Research (1995) “Approval Standard for Class I Panel Roofs, Class Number 4471”, August 1995.

COMMENTARY ON THE 1996 EDITION OF THE

SPECIFICATION FOR THE DESIGN OF COLD-FORMED STEEL STRUCTURAL MEMBERS 1996 EDITION SUPPLEMENT NO. 1

American Iron and Steel Institute

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Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1

The material contained herein has been developed by the American Iron and Steel Institute Committee on Specifications for the Design of Cold-Formed Steel Structural Members. The Committee has made a diligent effort to present accurate, reliable, and useful information on cold-formed steel design. The Committee acknowledges and is grateful for the contributions of the numerous researchers, engineers, and others who have contributed to the body of knowledge on the subject. Specific references are included in the Supplement to the Commentary on the Specification. With anticipated improvements in understanding of the behavior of cold-formed steel and the continuing development of new technology, this material may eventually become dated. It is anticipated that AISI will publish updates of this material as new information become available, but this can not be guaranteed. The materials set forth herein are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered professional engineer. Indeed, in most jurisdictions, such review is required by law. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.

1st Printing – April 2000

Produced by American Iron and Steel Institute Washington, DC Copyright American Iron and Steel Institute 2000

Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1

COMMENTARY ON AISI 1996 SPECIFICATION FOR THE DESIGN OF COLD-FORMED STEEL STRUCTURAL MEMBERS SUPPLEMENT NO. 1 JULY 30, 1999 1.

2.

Section A3.1 •

In the second paragraph, change “High-Strength, Low-Alloy (HSLA) steel” to “High-Strength, Low-Alloy Steel (HSLAS)”.

•

Make the following changes in the fourth paragraph: • Change the first sentence to “For the listed ASTM Standards, the yield points of steels range from 24 to 80 ksi (165 to 552 MPa) and ……”, • Change the third sentence to “Exceptions are ASTM A653 SS Grade 80, ASTM A611 Grade E, ASTM SS A792 SS Grade 80, and ASTM A875 SS Grade 80 ……”, and • Change “structural quality” in the last sentence to “SS”.

Section A3.3 •

Change “structural quality” to “SS” in the following locations: • Two places in the third sentence of the second paragraph, and • Two places in the first sentence of the fourth paragraph

•

In the third paragraph, add the following sentence after the sentence ending with “(Yu, 1991)”: Futher information on the test procedure should be obtained from “Standard Methods for Determination of Uniform and Local Ductility”, Cold-Formed Steel Design Manual, PartVIII (1996).

• Replace the last paragraph with the following: In the past, the limit of the yield point used in design to 75 percent of the specified minimum yield point, or 60 ksi (414 MPa), and the tensile strength used in design to 75 percent of the specified minimum tensile strength, or 62 ksi (427 MPa) whichever was lower, introduced a higher safety factor, but still made low ductility steels, such as SS Grade 80 and Grade E, useful for the named applications. Based on the recent UMR research findings (Wu, Yu, and LaBoube, 1996), Equation A3.3.2-1 is added in Section A3.3.2 under an Exception Clause to determine the reduced yield point, RbFy, for the calculation of the nominal flexural strength of multiple-web section such as roofing, siding and floor decking. For the unstiffened compression flange, Equation A3.3.2-2 is added on the basis of a 1988 UMR study (Pan and Yu, 1988). This new revision allows the use of a higher nominal bending strength than previous editions of the AISI Specification. When the multiple-web section is composed of both stiffened and unstiffened compression flange elements, the smallest Rb should be used to determine the reduced yield point for use on the entire section. Different values of the reduced yield point could be used for positive

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and negative moments. The equations provided in the Exception Clause can also be used for calculating the nominal flexural strength when the design strengths are determined on the basis of tests as permitted by the alternative method. It should be noted that the Exception Clause does not apply to the steel deck used for composite slabs when the deck is used as the tensile reinforcement. This limitation is to prevent the possible sudden failure of the composite slab due to lack of ductility of the steel deck. For the calculation of web crippling strength of deck panels, although the UMR study (Wu, Yu, and LaBoube, 1997) shows that the specified minimum yield point can be used to calculate the web crippling strength of deck panels, the Specification is adopting a conservative approach in Section C3.4.1. The lesser of 0.75 Fy and 60 ksi (414 MPa) is used to determine both the web crippling strength and the shear strength for the low ductility steels. This is consistent with the previous edition of the Specification. Another UMR study (Koka, Yu, and LaBoube, 1997) confirmed that for the connection design using SS Grade 80 of A653 steel, the tensile strength used in design should be taken as 75 percent of the specified minimum tensile strength or 62 ksi (427 MPa), whichever is less. It should be noted that the current AISI design provisions are limited only to the design of members and connections subjected to static loading without the considerations of fatigue strength. 3.

Section A7.1

Update the year of the ASTM A370 recent edition to “(ASTM, 1997)”, referenced in the first paragraph. 4.

Section A8 Change “of” to “or” in condition 2.

5.

Section B2.4 Add the following new section: B2.4 C-Section Webs With Holes Under Stress Gradient Studies of the behavior of web elements with holes conducted at the University of Missouri-Rolla(UMR) serve as the basis for the design recommendations for bending alone, shear, web crippling, combinations of bending and shear, and bending and web crippling (Shan et al., 1994; Langan et al., 1994; Uphoff, 1996; Deshmukh, 1996). The Specification considers a hole to be any flat punched opening in the web. The Specification does not address edge stiffened openings. The UMR design recommendations for a web with stress gradient are based on the tests of full-scale C-section beams having h/t ratios as large as 200 and d0/h ratios as large as 0.74. The test program considered only stud and joist industry standard web holes. These holes were rectangular with fillet corners, punched during the rolling process. For non-circular holes, the corner radii recommendation was adopted to avoid the potential of high stress concentration at the corners of a hole. Webs with circular holes and a stress gradient were not tested, however, the provisions are conservatively extended to cover this case. Other shaped holes must be evaluated by the virtual hole method described below, by test, or by other provisions of the Specification. The Specification is not intended to cover cross sections having

Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1

repetitive ½ in. diameter holes. Based on the study by Shan et al. (1994), it was determined that the nominal bending strength of a C-section with a web hole is unaffected when d0/h < 0.38. For situations where the d0/h ≥ 0.38, the effective depth of the web can be determined by treating the flat portion of the remaining web that is in compression as an unstiffened compression element. Although these provisions are based on tests of singly-symmetric C-sections having the web hole centered at mid-depth of the section, the provisions may be conservatively applied to sections for which the full unreduced compression region of the web is less than the tension region. However, for cross sections having a compression region greater than the tension region, the web strength must be determined by test in accordance with Section F1. The provisions for circular and non-circular holes also apply to any hole pattern that fits within an equivalent virtual hole. For example, Figure C-B2.4-1 illustrates the b and d0 that may be used for a multiple hole pattern that fits within a non-circular virtual hole. Figure C-B2.4-2 illustrates the d0 that may be used for a rectangular hole that exceeds the 2.5 in. (64 mm) by 4.5 in. (114 mm) limit but still fits within an allowed circular virtual hole. For each case, the design provisions apply to the geometry of the virtual hole, not the actual hole or holes. b d0

Figure C-B2.4-1 Virtual Hole Method for Multiple Openings

d0

Figure C-B2.4-2 Virtual Hole Method for Opening Exceeding Limit 6.

Section B6.1 Add the following paragraph to the end of the section: In 1999, the upper limit of w/ts ratio for the unstiffened elements of cold-formed steel transverse stiffeners has been revised from 0.37 E Fys to 0.42 E Fys for the reason that the former was calculated based on the allowable stress design approach, while the latter is based on effective area approach. The revision provides the same basis for the stiffened and unstiffened elements of cold-formed steel transverse stiffeners.

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Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1

Section C2 Revise the whole section as follows: C2 Tension Members As described in Specification Section C2, the nominal tensile strength of axially loaded cold-formed steel tension members is determined either by yielding of the gross area of the cross-section or by fracture of the net area of the cross section. At locations of connections, the nominal tensile strength is also limited by the capacities specified in Specification Sections E2.7, E3, and E4 for tension in connected parts. Yielding in the gross section indirectly provides a limit on the deformation that a tension member can achieve. The definition of yielding in the gross section to determine the tensile strength is well established in hot-rolled steel construction. For the LRFD Method, the resistance factor of φ t = 0.75 used for fracture of the net section is consistent with the φ factor used in the AISC LRFD Specification (AISC, 1993). The resistance factor φt = 0.90 used for yielding in the gross section was selected to be consistent with the AISC LRFD Specification (AISC, 1993).

8.

Section C3.1.2

Section C3.1.2, Lateral-Torsional Buckling, includes two subsections: C3.1.2.1, LateralTorsional Buckling Strength for Open Cross Section Members, and C3.1.2.2, LateralTorsional Buckling Strength for Closed Box Members. The content of both subsections is provided as follows: C3.1.2.1Lateral-Torsional Buckling Strength for Open Cross Section Members The bending capacity of flexural members is not only governed by the strength of the cross section, but can also be limited by the lateral-torsional buckling strength of the member if braces are not adequately provided. The design provisions for determining the nominal lateral-torsional buckling strength are given in Specification Section C3.1.2.1. If a doubly-symmetric or singly-symmetric member in bending is laterally unbraced, it can fail in lateral-torsional buckling. In the elastic range, the critical lateral-torsional buckling stress can be determined by Equation C-C3.1.2.1-1.  π 2 EC w  Aro = σ ey σ t EI y GJ 1 + (C-C3.1.2.1-1)  2  Sf GJL   In the above equation, σey and σt are the elastic buckling stresses as defined in Eq. C3.1.2.1-8 and Eq. C3.1.2.1-9, respectively, E is the modulus of elasticity, G is the shear modulus, Sf is the elastic section modulus of the full unreduced section relative to the extreme compression fiber, Iy is the moment of inertia about the y-axis, Cw is the torsional warping constant, J is the St. Venant torsion constant, and L is the unbraced length. For equal-flanged I-members, equation C-C3.1.2.1-2 can be used to calculate the elastic critical buckling stress (Winter, 1947a; Yu, 1991): σ cr =

π LSf

Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1 2

  L  2 JI y  Iy       + σ cr = (C-C3.1.2.1-2)  2I    πd 2 2 x 2(L/d)    2(1 + µ)I x   In Equation C-C3.1.2.1-2, the first term under the square root represents the lateral bending rigidity of the member, and the second term represents the St. Venant torsional rigidity. For thin-walled cold-formed steel sections, the first term usually exceeds the second term by a considerable margin. For I-members with unequal flanges, the following equation has been derived by Winter for the lateral-torsional buckling stress (Winter, 1943):   π 2 Ed  4GJL2  σ cr = I I + I 1 + (C-C3.1.2.1-3) y  yc yt  π 2 I y Ed 2  2L2 S f    where Iyc and Iyt are the moments of inertia of the compression and tension portions of the full section, respectively, about the centroidal axis parallel to the web. Other symbols were defined previously. For equal-flange sections, Iyc = Iyt = Iy/2, Equations C-C3.1.2.1-2 and C-C3.1.2.1-3 are identical. In Equation C-C3.1.2.1-3, the second term under the square root represents the St. Venant torsional rigidity, which can be neglected without any loss in economy. Therefore, Equation C-C3.1.2.1-3 can be simplified as shown in Equation C-C3.1.2.14 by considering Iy = Iyc + Iyt and neglecting the term 4GJL2/π2IyEd2: π2 E

σ cr =

π 2 EdI yc

(C-C3.1.2.1-4) L2 S f Equation C-C3.1.2.1-4 was derived on the basis of a uniform bending moment and is conservative for other cases. For this reason σcr is modified by multiplying by a bending coefficient Cb, to account for non-uniform bending, i.e., C b π 2 EdI yc

(C-C3.1.2.1-5) L2 S f where Cb is the bending coefficient, which can conservatively be taken as unity, or calculated from Cb =1.75 + 1.05 (M1/M2) + 0.3 (M1/M2)2 ≤ 2.3 (C-C3.1.2.1-6) in which M1 is the smaller and M2 the larger bending moment at the ends of the unbraced length. The above Equation was used in the 1968, 1980, 1986, and 1991 editions of the AISI Specification. Because it is valid only for straight-line moment diagrams, Equation C-C3.1.2.1-6 is replaced by the following equation for Cb in the 1996 edition of the Specification: 12.5Mmax Cb = (C-C3.1.2.1-7) 2.5Mmax + 3M A + 4M B + 3MC Fe =

where Mmax = absolute value of maximum moment in the unbraced segment MA

= absolute value of moment at quarter point of unbraced segment

MB

= absolute value of moment at centerline of unbraced segment

MC = absolute value of moment at three-quarter point of unbraced segment Equation C-C3.1.2.1-7, derived from Kirby and Nethercot (1979), can be used

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for various shapes of moment diagrams within the unbraced segment. It gives more accurate solutions for fixed-end members in bending and moment diagrams which are not straight lines. This equation is the same as that being used in the AISC LRFD Specification (AISC, 1993). Figure C-C3.1.2.1-1 shows the differences between Equations C-C3.1.2.1-6 and C-C3.1.2.1-7 for a straight line moment diagram. C b = 1.75 + 1.05

2.5

M1 M2

+ 0.3

M1 2 < 2.3 M2

2.0

1.5 Cb 1.0

0.5

+1.0

Cb =

12.5M max 2.5Mmax+ 3MA+ 4M B+3M C

MA MB MC

M2

M1

+0.5

0

-0.5

-1.0

M1 M2

Figure C-C3.1.2.1-1 Cb for Straight Line Moment Diagram

It should be noted that Equations C-C3.1.2.1-1 and C-C3.1.2.1-5 apply only to elastic buckling of cold-formed steel members in bending when the computed theoretical buckling stress is less than or equal to the proportional limit. When the computed stress exceeds the proportional limit, the beam behavior will be governed by inelastic buckling. The inelastic buckling stress can be computed from Equation CC3.1.2.1-8 (Yu, 1991): 10  10Fy  Fc = Fy 1 − (C-C3.1.2.1-8)  36F  9 e  The elastic and inelastic critical stresses for the lateral-torsional buckling strength are shown in Figure C-C3.1.2.1-2. For any unbraced length, L, less than Lu, lateral-torsional buckling does not need to be considered. Fc 10 F 9 y

I- and Z-sections (1986 Specification)

Fy C-Sections (1986 Specification)

0.56Fy

0 0

Lu

Unbraced Length, L

Figure C-C3.1.2.1-2 Lateral-Torsional Buckling Strength

Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1

Equations C-C3.1.2.1-5 and C-C3.1.2.1-8 were used in the 1968, 1980 and 1986 editions of the AISI Specification to develop the allowable stress design equations for lateral-torsional buckling of I-members. In the 1986 edition of the AISI Specification, in addition to the use of Equations C-C3.1.2.1-5 and C-C3.1.2.1-8 for determining the critical moments, more design equations (Specification Equations C3.1.2.1-5 and C3.1.2.1-6) for elastic critical moment were added as alternative methods. These additional equations were developed from the previous studies conducted by Pekoz, Winter and Celebi on torsional-flexural buckling of thin-walled sections under eccentric loads (Pekoz and Winter, 1969a; Pekoz and Celebi, 1969b) and are retained in the 1996 and this edition of the Specification. These general design equations can be used for singly-, doubly- and point-symmetric sections. It should be noted that point-symmetric sections such as Z-sections with equal flanges will buckle laterally at lower strengths than doubly- and singly-symmetric sections. A conservative design approach has been and is being used in the Specification, in which the elastic critical buckling stress is taken to be one-half of that for I-members. Regarding the inelastic critical buckling stress, the following equation was used for calculating the critical moment in the 1986 edition of the Specification instead of Equation C-C3.1.2.1-8 for singly-symmetric sections: My   (C-C3.1.2.1-9) (Mcr)I = M y 1 −   4(M cr ) e  in which (Mcr)I is the elastic critical buckling moment. In 1996, the basic inelastic lateral buckling curve for singly-, doubly-, and point-symmetric sections in Specification Section C3.1.2.1(a) has been redefined to be consistent with the inelastic lateral buckling curve for I- or Z-sections in Specification Section C3.1.2.1(b). The general shape of the curve as represented by Equation C-C3.1.2.1-8 is also consistent with the preceding edition of the Specification (AISI, 1980). As specified in Specification Section C3.1.2.1, lateral-torsional buckling is considered to be elastic up to a stress equal to 0.56Fy. The inelastic region is defined by a Johnson parabola from 0.56Fy to (10/9)Fy at an unsupported length of zero. The (10/9) factor is based on the partial plastification of the section in bending (Galambos, 1963). A flat plateau is created by limiting the maximum stress to Fy which enables the calculation of the maximum unsupported length for which there is no stress reduction due to lateral instability. This maximum unsupported length can be calculated by setting Fy equal to Fc in Equation C-C3.1.2.1-8. This liberalization of the inelastic lateral-torsional buckling curve for singly-, doubly-, and point-symmetric sections has been confirmed by research in beamcolumns (Pekoz and Sumer, 1992) and wall studs (Niu and Pekoz, 1994). The above discussion dealt only with the lateral-torsional buckling strength of locally stable beams. For locally unstable beams, the interaction of the local buckling of the compression elements and overall lateral-torsional buckling of members may result in a reduction of the lateral-torsinal buckling strength of the member. The effect of local buckling on the critical moment is considered in Section C3.1.2.1 of the AISI Specification by using the elastic section modulus Sc based on an effective section. Mn =FcSc (C-C3.1.2.1-10) where Fc = Elastic or inelastic critical lateral-torsional buckling stress Sc = Elastic section modulus of effective section calculated at a stress Fc relative to the extreme compression fiber Using the above nominal lateral buckling strength with a resistance factor of

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φb = 0.90, the values of β vary from 2.4 to 3.8 for the LRFD method. The research conducted by Ellifritt, Sputo and Haynes (1992) has indicated that when the unbraced length is defined as the spacing between intermediate braces, the equations used in Specification Section C3.1.2.1 may be conservative for cases where one mid-span brace is used, but may be unconservative where more than one intermediate brace is used. The above mentioned research (Ellifritt, Sputo, and Haynes, 1992) and the study of Kavanagh and Ellifritt (1993 and 1994) have shown that a discretely braced beam, not attached to deck and sheathing, may fail either by lateral-torsional buckling between braces, or by distortional buckling at or near the braced point. The distortional buckling strength of C- and Z-sections has been studied extensively at the University of Sydney by Lau and Hancock (1987); Hancock, Kwon and Bernard (1994); and Hancock (1995). The problems discussed above dealt with the type of lateral-torsional buckling of I-members, channels, and Z-shaped sections for which the entire cross section rotates and deflects in the lateral direction as a unit. But this is not the case for Ushaped beams and the combined sheet-stiffener sections as shown in Figure CC3.1.2.1-3. For this case, when the section is loaded in such a manner that the brims and the flanges of stiffeners are in compression, the tension flange of the beam remains straight and does not displace laterally; only the compression flange tends to buckle separately in the lateral direction, accompanied by out-of-plane bending of the web, as shown in Figure C-C3.1.2.1-4, unless adequate bracing is provided.

Figure C-C3.1.2.1-3 Combined Sheet-Stiffener Sections

Figure C-C3.1.2.1-4 Lateral Buckling of U-Shaped Beam The precise analysis of the lateral buckling of U-shaped beams is rather complex. The compression flange and the compression portion of the web act not only like a column on an elastic foundation, but the problem is also complicated by the weakening influence of the torsional action of the flange. For this reason, the design procedure outlined in Section 2 of Part VII (Supplementary Information) of the AISI Cold-Formed Steel Design Manual (AISI, 1996) for determining the allowable design strength for laterally unbraced compression flanges is based on the considerable simplification of an analysis presented by Douty (1962). In 1964, Haussler presented rigorous methods for determining the strength of

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elastically stabilized beams (Haussler, 1964). In his methods, Haussler also treated the unbraced compression flange as a column on an elastic foundation and maintained more rigor in his development. A comparison of Haussler’s method with Douty’s simplified method indicates that the latter may provide a lower value of critical stress. An additional study of laterally unbraced compression flanges has been made at Cornell University (Serrette and Pekoz, 1992, 1994 and 1995). An analytical procedure has been developed for determining the distortional buckling strength of the standing seam roof panel. The predicted maximum capacities have been compared with experimental results. C3.1.2.2 Lateral-Torsional Buckling Strength for Closed Box Members Due to the high torsional stiffness of closed box sections, lateral-torsional buckling is not critical in typical design considerations, even for bending about the major axis. Deflection limits will control most designs due to the large values of Lu. However, lateral-torsional buckling can control the design when the unbraced length is larger than Lu, which is determined by setting the inelastic buckling stress of Eq. C3.1.2.1-3 equal to Fy, the yield stress with Fe set equal to Eq. C3.1.2.2-2. In computing the lateral-torsional buckling stress of closed box sections, the warping constant, Cw, may be neglected since the effect of non-uniform warping of box sections is small. The development of Eq. C3.1.2.2-2 can be found in the SSRC Guide (Galambos, 1998). As a result of adding Section C3.1.2.2 to the Specification, Section D3.3 has been deleted. The torsional constant, J, of a box section, neglecting the corner radii, may be conservatively determined as follows: J=

2(ab) 2 (a / t 1 ) + ( b / t 2 )

(Eq. C-C3.1.2.2-1)

where a = Distance between web centerlines b = Distance between flange centerlines t1 = Thickness of flanges t2 = Thickness of webs 9.

Section C3.1.3 • Add “; Fisher, 1996” after “Haussler, 1988” at the end of the first paragraph. • Insert the following paragraph after the first paragraph: The R factors for simple span C-sections up to 8.5 inches in depth and Zsections up to 9.5 inches in depth have been increased from the 1986 Specification, and a member design yield strength limit is added based on the work by Fisher (1996). •

Delete the second sentence in the paragraph starting with “As indicated by LaBoube……”.

10. Section C3.1.4 •

In the first sentence, delete “under gravity load,” and add “or uplift from wind load,”

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• • •

after “subjected to dead plus live load,”. Change “The bending strength” to “The bending capacity” in the second sentence. Delete “(1996)” at the end of the third sentence. Change the last two sentences to “In Specification Equation C3.1.4-1, the reduction factor, R, can be determined by the test procedures, which were established in 1996 and are included in Part VIII of the AISI Cold-Formed Steel Design Manual (AISI, 1996). Application of the base test method for uplift loading was subsequently validated after further analysis of the research results.”

11. Section C3.1.5 Add the following new section: C3.1.5 Strength of Standing Seam Roof Panel Systems The nominal strength of a standing seam roof panel system is determined using the ASTM E1592-95 (1995) test procedure. A methodology of interpreting test results is specified in the Specification Section C3.1.5. Clarification and extension of the ASTM E1592-95 (1995) test procedure is presented in the Standard Procedures for Panel and Anchor Structural Tests in Part VIII of the AISI Cold-Formed Steel Design Manual. The Specification Section C3.1.5 provides the method for the calculation of a safety factor for one or more tests. The relationship of strength to serviceability limits may be taken as strength limit/serviceability limit = 1.25, or Ω serviceability = Ωstrength/1.25

(Eq. C-C3.1.5-1)

It should be noted that the purpose of the test procedure specified in Specification Section C3.1.5 is not to set up guidelines to establish the serviceability limit. The purpose is to define the method of determining the controlling allowable load whether based on the serviceability limit or on the ultimate load. The Corps of Engineers Procedure CEGS 07416 (1991) requires a safety factor of 1.65 on strength and 1.3 on serviceability. A buckling or crease does not have the same consequences as a failure of a clip. In the latter case, the roof panel itself may become detached and expose the contents of a building to the elements of the environment. Further, Galambos (1988) recommended a value of 2.0 for β 0 when slight damage is expected and a value of 2.5 when moderate damage is expected. The resulting ratio is 1.25. In Section C3.1.5, a target reliability of 2.5 is used for connection limits. It is used because the consequences of a panel fastener failure (β 0 = 2.5) are not nearly so severe as the consequences of a primary frame connection failure (β 0 = 3.5). The intermittent nature of wind load as compared to the relatively long duration of snow load further justifies the use of β 0 = 2.5 for panel anchors. In Section C3.1.5, the coefficient of variation of the material factor, VM, is recommended to be 0.08 for failure limited by anchor or connection failure, and 0.10 for limits caused by flexural or other modes of failure. Section C3.1.5 also eliminates the limit on coefficient of variation of the test results, Vp, because consistent test results often lead to Vp values lower than the 6.5% value set in Specification Section F1. The elimination of the limit will be beneficial when test results are consistent. The value for the number of tests for fasteners is set as the number of anchors tested with the same tributary area as the anchor that failed. This is consistent with design practice where anchors are checked using a load calculated based on tributary

Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1

area. Actual anchor loads are not calculated from a stiffness analysis of the panel in ordinary design practice. 12. Section C3.2 This section contains two subsections: C3.2.1, Shear Strength of Webs Without Holes, and C3.2.2, Shear Strength of C-Section Webs With Holes. Section C3.2.1 contains the content of current Section C3.2 with revisions described below, and Section C3.2.2 is a new added section as provided subsequently: • Add subsection title “C3.2.1, Shear Strength of Webs Without Holes” after the section title. • Change the equation numbers in current Section C3.2 to “(C-C3.2.1-”, and revise the section reference from “C3.2” to “C3.2.1” both in the fifth and the last paragraphs. • Add the follow new section: C3.2.2 Shear Strength of C-Section Webs With Holes Schuster et al. (1995) and Shan et al. (1994) investigated the degradation in web shear strength due to the presence of a web perforation. The test program considered a constant shear distribution across the perforation, and included d0/h ratios ranging from 0.20 to 0.78, and h/t ratios of 91 to 168. Schuster’s qs equation was developed with due consideration for the potential range of both punched and field cut holes. Three hole geometries, rectangular with corner fillets, circular, and diamond, were considered in the test program. Eiler (1997) extended the work of Schuster and Shan for the case of constant shear along the longitudinal axis of the perforation. He also studied linearly varying shear but this case is not included in the Specification. The development of Eiler’s reduction factor, qs, utilized the test data of both Schuster et al. (1995) and Shan et al. (1994). The focus of the test programs was on the behavior of slender webs with holes. Thus for stocky web elements with h/t ≤ 0.96 Ek v /Fy , an anomaly exists; the calculated design shear strength is independent of t when h is constant. In this region, the calculated design shear strength is valid but may be somewhat conservative. The provisions for circular and non-circular holes also apply to any hole pattern that fits within an equivalent virtual hole. Figure C-B2.4-1 illustrates the b and d0 that may be used for a multiple hole pattern that fits within a non-circular virtual hole. Figure C-B2.4-2 illustrates the d0 that may be used for a rectangular hole that fits within a circular virtual hole. For each case, the design provisions apply to the geometry of the virtual hole geometry, not the actual hole or holes 13. Section C3.4 This section includes two subsections: C3.4.1, Web Crippling Strength of Webs Without Holes, and C3.4.2, Web Crippling Strength of C-Section Webs With Holes. Section C3.4.1 contains the contents of current Section C3.4 with revisions described below, and Section C3.4.2 is a new added section as provided subsequently: • Add the subsection title “C3.4.1, Web Crippling Strength of Webs Without Holes” after the section title. • Replace the seventh paragraph in current Section C3.4 with the following:

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In the 1996 edition of the AISI Specification, HSLAS Grades 70 and 80 of A653 and A715 steels were added in Specification Section A3.1. These two grades of steels have minimum yield points of 70 ksi (483 MPa) for grade 70 and 80 ksi (552 MPa) for grade 80. Because the AISI provisions for web crippling strength were previously developed on the basis of the experimental investigations using steels having Fy less than 55 ksi (379 MPa) (Hetrakul and Yu, 1978), previous Specification Equations C3.4-1, C3.4-2, and C3.4-6 were limited only to Fy < 66.5 ksi (459 MPa). For this reason, when Fy ≥ 66.5 ksi (459 MPa), the value of kC3 was taken as 1.34 in the 1996 edition of the Specification. Recent research at the University of MissouriRolla (Wu, Yu and LaBoube, 1997) indicated that the web crippling strength increased for beams using the yield point of steel greater than 66.5 ksi (459 MPA). Based on the results of 262 web crippling tests using yield strengths from 58.2 ksi (401 MPa) to 165.1 ksi (1138 MPa), the constant C3 is replaced by C1 in Equations C3.4.1-1, C3.4.1-2 and C3.4.1-6 of the Specification. The upper limit of the design yield point for A653 SS Grade 80 and A611 Grade E steels is defined by Section A3.3.2 and is the lesser of 0.75 Fy and 60 ksi (414 MPa). • Add the following new section: C3.4.2 Web Crippling Strength of C-Section Webs With Holes Studies by Langan et al. (1994), Uphoff (1996) and Deshmukh (1996) quantified the reduction in web crippling capacity when a hole is present in a web element. These studies investigated both the end-one-flange and interior-one-flange loading conditions for h/t and d0/h ratios as large as 200 and 0.81, respectively. The studies revealed that the reduction in web crippling strength is influenced primarily by the size of the hole as reflected in the d0/h ratio and the location of the hole, x/h ratio. The provisions for circular and non-circular holes also apply to any hole pattern that fits within an equivalent virtual hole. Figure C-B2.4-1 illustrates the b and d0 that may be used for a multiple hole pattern that fits within a non-circular virtual hole. Figure C-B2.4-2 illustrates the d0 that may be used for a rectangular hole that fits within a circular virtual hole. For each case, the design provisions apply to the geometry of the virtual hole geometry, not the actual hole or holes. 14. Section C4 Add the following to the end of the section: The slenderness ratio, KL/r, of all compression members preferably should not exceed 200, except that during construction only, KL/r should not exceed 300. In 1999, the above recommendations were moved from the Specification to the Commentary. The maximum slenderness ratios on compression and tension members have been stipulated in steel design standards for many years but are not mandatory in the AISI Specification. The KL/r limit of 300 is still recommended for most tension members in order to control serviceability issues such as handling, sag and vibration. The limit is not mandatory, however, because there are a number of applications where it can be shown that such factors are not detrimental to the performance of the structure or assembly of which the member is a part. Flat strap tension bracing is a common example of an acceptable type of tension member where the KL/r limit of 300 is

Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1

routinely exceeded. The compression member KL/r limits are recommended not only to control handling, sag and vibration serviceability issues but also to flag possible strength concerns. The AISI Specification provisions adequately predict the capacities of slender columns and beam-columns but the resulting strengths are quite small and the members relatively inefficient. Slender members are also very sensitive to eccentrically applied axial load because the moment magnification factors given by 1/α will be large. 15. Section C6.1 •

In the third paragraph, after the second sentence add the sentence “In 1999, the bounds of Specification Equations C6.1-1 and C6.1-2 have been revised to provide an appropriate continuity.” • Revise the D/t values on Figure C-C6.1-1 from “0.319E/Fy” to “0.318E/Fy” and 0.70E/Fy” to “0.0714E/Fy”.

16. Section C6.2 Add the following paragraph to the end of the section: In 1999, the coefficient, R, was limited to one so that the effective area, Ae, will always be less than or equal to the unreduced cross sectional area, A. To simplify the equations, R = Fy/2Fe rather than R = Fy 2Fe as in the previous Specification edition. 17. Section D3.2.1 • • •

Revise the first sentence to “In metal roof systems attached to C- or Z-purlins, ……”. Revise the equation numbers in the fourth sentence of the first paragraph and the second sentence of the second paragraph to “……Equations D3.2.1-2 through D3.2.1-7……”. Add the following paragraph to the end of the section: In 1999, an explicit requirement is indicated for purlins facing opposite directions to resist the down-slope component of the total gravity load. To have a consistent approach in calculating the restraint force for C- and Z-sections, Equation D3.2.1-1 is added for calculating the anchorage force for C-sections. In addition, “cosθ” term is added to the first term of Equation D3.2.1-1 for C-sections and Equations D3.2.1-2 through D3.2.1-7 for Z-sections. The original research was done assuming the roof was flat and the applied loading was parallel to the purlin webs. In the equations, Wcosθ is the component of the vertical loading parallel to the purlin webs.

18. Section D3.3 As a result of adding Section C3.1.2.2, Lateral-Torsional Buckling Strength for Closed Box Members, Section D3.3 is deleted.

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19. Section E2 The following changes are made in response to the updates of the AWS Structural Welding Code for Sheet Steel: • Change the year of the recent edition of the AWS Structural Welding Code for Sheet Steel to “(AWS, 1998)” referenced in the fourth paragraph and the sixth paragraph of Section E2. • At the end of Section E2.1, add the sentence “Prequalified joint details are given in AWS D1.3-98 (AWS, 1998).” • At the end of Section E2.2, add the sentence “The provisions of Section E2.2 apply to plug welds as well as spot welds.” • In the second paragraph of Section E2.4, correct the referenced author’s name to “McGuire”, and at the end of the second paragraph add the sentence “Prequalified fillet welds are given in AWS D1.3-98 (AWS, 1998).” • The weld illustrations in Figures C-E2.4-1 and CE2.5-1 are revised to reflect the good quality of prequalified welds:

A-A A

a. Transverse Fillet Sheet Tear

b. Longitudinal Fillet Sheet Tear

Figure C-E2.4-1 Fillet Weld Failure Mode

Transverse Sheet Tear

Longitudinal Sheet Tear

Figure C-E2.5-1 Flare Groove Weld Failure Modes • In the third paragraph of Section E2.5, revise the third sentence to “This weld is a prequalified weld in AWS D1.3-98 (AWS, 1998)……”.

Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1

20. Section E2.6 • • • • •

Delete “listed” from the first sentence. Change “0.125 inch (3.22 mm)” to “0.125 in. (3.18 mm)” in both the first and the second sentences. Change “(2.7 N/m2)” to “(275 g/m2)”. Delete “Values for intermediate thicknesses may be obtained by straight line interpolation.” Add the following paragraph to the end of the section: In 1999, a design equation is used to determine the nominal shear strength which replaces the tabulated values given in the previous specifications. The upper limit of Eqs. E2.6-1 and E2.6-3 is selected to best fit the data provided in AWS C1.370, Table 2.1 and AWS C1.1-66, Table 1.3. Shear strength values for welds with the thickness of the thinnest outside sheet greater than 0.180 in. (4.57 mm) have been excluded in (Eq. E2.6-2) and (Eq. E2.6-4) due to the thickness limit set forth in Section E2.

21. Section E2.7 Add the following new sections: E2.7 Shear Lag Effect in Welded Connections of Members Other Than Flat Sheets Shear lag has a debilitating effect on the nominal tensile strength of a cross section. The AISI Specification addresses the shear lag effect on tension members other than flat sheets in welded connections. The AISC Specification’s design approach has been adopted. When computing U for combinations of longitudinal and transverse welds, L is taken as the length of the longitudinal weld because the transverse weld does little to minimize shear lag. For angle or channel sections , the distance, x , from shear plane to centroid of the cross section is defined in Figure C-E2.7.

22. Section E3.2 • In the first sentence, change “on the net section” to “of the net section”. • Change item 4 to “The nominal tensile strength……”.

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• Add the following paragraphs to the end of the section: The presence of staggered or diagonal hole patterns in a bolted connection has long been recognized as increasing the net section area for the limit state of fracture in the net section. LaBoube and Yu (1995) summarized the findings of a limited study of the behavior of bolted connections having staggered hole patterns. The research showed that when a staggered hole pattern is present, the width of a fracture plane can be adjusted by use of s′2/4g. Because of the lack of test data necessary for a more accurate design formulation, a discontinuity between AISI and AISC cannot be avoided. The presence of a discontinuity should not be a significant design issue because the use of the staggered hole patterns is not common in cold-formed steel applications. Shear lag has a debilitating effect on the tensile capacity of a cross section. Based on UMR research (LaBoube and Yu, 1995) design equations have been developed that can be used to estimate the influence of the shear lag. The research demonstrated that the shear lag effect differs for an angle and a channel. For both cross sections, however, the key parameters that influence shear lag are the distance from the shear plane to the center of gravity of the cross section and the length of the bolted connection (Fig. C-E3.2). The research showed that for single bolt connections, bearing controlled the nominal strength, not fracture in the net section.

The value for φ used with Eq. E3.2-8 is based on statistical analysis of the test data with a corresponding value of β = 35 . . The Ω values are unchanged from previous editions of the ASD Specification. 23. Section E3.3 Add the following paragraphs to the end of the section: Based on research at the University of Missouri-Rolla (LaBoube and Yu, 1995), design equations have been developed that recognize the presence of hole elongation prior to reaching the limited bearing strength of a bolted connection. The researchers adopted an elongation of 0.25 in. (6.4 mm) as the acceptable deformation limit. This limit is consistent with the permitted elongation prescribed for hot-rolled steel. Research at the University of Sydney (Rogers and Hancock, 1998), has shown that the bearing coefficient for steels of thickness less than 0.036 in (0.91 mm) may be significantly less than 3.0. A lower limit of 0.036 in (0.91 mm) has therefore been chosen for Table E3.3-1.

Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1

24. Section E5 Replace the whole section with the following: E5 Fracture Connection tests conducted by Birkemoe and Gilmor (1978) have shown that on coped beams a tearing failure mode as shown in Figure C-E5-1(a) can occur along the perimeter of the holes. Hardash and Bjorhovde (1985) have demonstrated these effects for tension members as illustrated in Figure C-E5-1(b) and Figure C-E5-2. The provisions provided in Specification Section E5 for shear rupture have been adopted from the AISC Specification (AISC, 1978). For additional design information on tension rupture strength and block shear rupture strength of connections (Figures C-E5-1 and C-E5-2), refer to the AISC Specifications (AISC, 1989 and 1993).

Cope Beam

Shear area

Failure by tearing out of shaded portion

Failure by tearing out of shaded portion Shear area Tensile area

Tensile area

Po (a)

(b)

Figure C-E5-1 Fatigue Modes for Block Shear Rupture

Po Po Small tension force

Large tension force

Large shear force

Po (a)

Po

Small shear force

(b)

Figure C-E5-2 Block Shear Rupture in Tension

Block shear is a limit state in which the resistance is determined by the sum of the shear strength on a failure path(s) parallel to the force and the tensile strength on the segment(s) perpendicular to the force, as shown in Figure C-E5-2. A comprehensive test program does not exist regarding block shear for cold-formed steel members. However, a limited study conducted at the University of Missouri-Rolla indicates that the AISC LRFD equations may be applied to cold-formed steel members. The φ and Ω values for block shear were taken from the 1996 edition of the Specification, and are based on the performance of fillet welds. In calculating the net

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Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1

web area Awn, the web depth is taken as the flat portion of the web as illustrated in Fig. C-E5-3.

hwc

Figure C-E5-3 Definition of hwc

25. Section E6.1 Replace the whole section with the following: The design provisions for the nominal bearing strength on the other materials should be derived from appropriate material specifications. 26. Section F1 Add the following paragraph to the end of the section: In 1999, two entries were added to Table F1, one for "Structural Members Not Listed Above" and the other for "Connections Not Listed Above". It was considered necessary to include these values for members and connections not covered by one of the existing classifications. The statistical values were taken as the most conservative values in the existing table. 27. Section F3.3 Update the year of the ASTM A370 recent edition to “(1997)”. 28. REFERENCES: The following references are added or updated: American Society for Testing Materials (1995), “Standard Test Method for Structural Performance of Sheet Metal Roof and Siding Systems by Uniform Static Air Pressure Difference,” E 1592-95, 1995. American Society for Testing and Materials (1997), “Standard Methods and Definitions for Mechanical Testing of Steel Products,” ASTM 370, 1997. American Welding Society (1998), Structural Welding Code - Sheet Steel, ANSI/AWS D1.3-98, Miami, FL, 1998. Deshmukh, S. U. (1996), "Behavior of Cold-Formed Steel Web Elements with Web Openings Subjected to Web Crippling and a Combination of Bending and Web Crippling for Interior-One-Flange Loading," thesis presented to the faculty of the University of Missouri-Rolla in partial fulfillment for the degree Master of Science.

Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1

Eiler, M. R., LaBoube, R. A., and Yu, W.W. (1997), “Behavior of Web Elements with Openings Subjected to Linearly Varying Shear,” Final Report, Civil Engineering Series 97-5, Cold-Formed Steel Series, Department of Civil Engineering, University of Missouri-Rolla Fisher, J. M., (1996), “Uplift Capacity of Simple Span Cee and Zee Members with Through - Fastened Roof Panels,” Final Report MBMA 95-01, Metal Building Manufacturers Association, 1996. Galambos, T. V. (1998), Guide to Stability Design Criteria for Metal Structures, 5th Edition, John Wiley & Sons, Inc., 1998. Galambos, T. V. (1988), “Reliability of Structural Steel Systems, “ Report No. 88-06 published by AISI, 1988. Hardash, S. G., and Bjorhovde, R. (1985), “New Design Criteria for Gusset Plates in Tension,” AISC Engineering Journal, Vol. 22, No. 2, 2nd Quarter. Koka, E.N., W. W. Yu and R. A. LaBoube (1997), “Screw and Welded Connection Behavior Using Structural Grade 80 of A653 Steel (A Preliminary Study),” Fourth Progress Report, Civil Engineering Study 97-4, University of Missouri-Rolla, Rolla, MO, June 1997. LaBoube, R. A., and Yu, W. W. (1995), “Tensile and Bearing Capacities of Bolted Connections,” Final Summary Report, Civil Engineering Study 95-6, Cold-Formed Steel Series, Department of Civil Engineering, University of Missouri-Rolla. Langan, J. E., LaBoube, R. A., and Yu, W. W. (1994), "Structural Behavior of Perforated Web Elements of Cold-Formed Steel Flexural Members Subjected to Web Crippling and a Combination of Web Crippling and Bending," Final Report, Civil Engineering Series 94-3, Cold-Formed Steel Series, Department of Civil Engineering, University of Missouri-Rolla Pan, L.C., and W. W. Yu (1988), "High Strength Steel Members with Unstiffened Compression Elements," Proceedings of the Ninth International Specialty Conference on Cold-Formed Steel Structures, University of Missouri-Rolla, MO, November, 1988. Rogers, C. A., and Hancock, G. J. (1998), “Bolted Connection Tests of Thin G550 and G300 Sheet Steels,” Journal of Structural Engineering, ASCE, Vol. 124, No. 7, 1998. Shan, M. Y., LaBoube, R. A., and Yu, W. W. (1994), "Behavior of Web Elements with Openings Subjected to Bending, Shear and the Combination of Bending and Shear," Final Report, Civil Engineering Series 94-2, Cold-Formed Steel Series, Department of Civil Engineering, University of Missouri-Rolla Schuster, R. M., Rogers, C. A., and Celli, A. (1995), "Research into Cold-Formed Steel Perforated C-Sections in Shear," Progress Report No. 1 of Phase I of CSSBI/IRAP Project, Department of Civil Engineering, University of Waterloo, Waterloo, Ontario Canada United States Army Corps of Engineers (1991), “Guide Specification for Military Construction, Standing Seam Metal Roof Systems”, October 1991. Uphoff, C. A. (1996), "Structural Behavior of Circular Holes in Web Elements of Cold-Formed Steel Flexural Members Subjected to Web Crippling for End-OneFlange Loading," thesis presented to the faculty of the University of Missouri-Rolla in partial fulfillment for the degree Master of Science.

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Wu, S., W. W. Yu and R. A. LaBoube (1996), “Strength of Flexural Members Using Structural Grade 80 of A653 Steel (Deck Panel Tests),” Second Progress Report, Civil Engineering Study 96-4, University of Missouri-Rolla, Rolla, MO, November 1996. Wu, S., W. W. Yu and R. A. LaBoube (1997), “Strength of Flexural Members Using Structural Grade 80 of A653 Steel (Web Crippling Tests),” Third Progress Report, Civil Engineering Study 97-3, University of Missouri-Rolla, Rolla, MO, February 1997.

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