Aisi Specifications Supplement 1 - 1996 Specification for the Design of Cold-Formed Steel Structural...

FOR COLD-

STRUCTU

American

SPECIFICATIONTHE DESIGN OFFORMED STEELRAL MEMBERS

With Commentary

1996 EDITION

SUPPLEMENT NO. 1

July 30, 1999

Iron and Steel Institute

SPECIFICATIONFOR THE DESIGN OF

COLD-FORMEDSTEEL STRUCTURAL

MEMBERS

1996 EDITION

SUPPLEMENT NO. 1

American Iron and Steel Institute

2 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 SteelInstitute Committee on Specifications for the Design of Cold-Formed Steel StructuralMembers. The Committee has made a diligent effort to present accurate, reliable, anduseful information on cold-formed steel design. The Committee acknowledges and isgrateful for the contributions of the numerous researchers, engineers, and others whohave contributed to the body of knowledge on the subject. Specific references areincluded in the Supplement to the Commentary on the Specification.

With anticipated improvements in understanding of the behavior of cold-formedsteel and the continuing development of new technology, this material may eventuallybecome dated. It is anticipated that AISI will publish updates of this material as newinformation become available, but this can not be guaranteed.

The materials set forth herein are for general information only. They are not asubstitute for competent professional advice. Application of this information to a specificproject should be reviewed by a registered professional engineer. Indeed, in mostjurisdictions, such review is required by law. Anyone making use of the information setforth herein does so at their own risk and assumes any and all resulting liability arisingtherefrom.

1st Printing – April 2000

Produced by American Iron and Steel InstituteWashington, DC

Copyright American Iron and Steel Institute 2000

Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1 3

TABLE OF CONTENTSAISI 1996 SPECIFICATION FOR THE DESIGN OF

COLD-FORMED STEEL STRUCTURAL MEMBERSSUPPLEMENT NO. 1

Section A3.1........................................................................................................................................................ 5Section A3.3........................................................................................................................................................ 5Section A5.1.3 ..................................................................................................................................................... 6Section A9........................................................................................................................................................... 6Section B1.1 ........................................................................................................................................................ 7Section B2.4 ........................................................................................................................................................ 7

B2.4 C-Section Webs With Holes Under Stress Gradient ............................................................... 7Section B6.1 ........................................................................................................................................................ 8Section C2 ........................................................................................................................................................... 8

C2 Tension Members .................................................................................................................... 8Section C3.1 ........................................................................................................................................................ 9Section C3.1.2 ..................................................................................................................................................... 9

C3.1.2.1 Lateral-Torsional Buckling Strength for Open Cross Section Members................................. 9C3.1.2.2 Lateral-Torsional Buckling Strength for Closed Box Members............................................ 11

Section C3.1.3 ................................................................................................................................................... 12C3.1.3 Beams having One Flange Through-Fastened to Deck or Sheathing.................................... 12

Section C3.1.4 ................................................................................................................................................... 13Section C3.1.5 ................................................................................................................................................... 13

C3.1.5 Strength for Standing Seam Roof Panel Systems.................................................................. 13Section C3.2 ...................................................................................................................................................... 14

C3.2.2 Shear Strength of C-Section Webs With Holes ..................................................................... 14Section C3.4 ...................................................................................................................................................... 15

C3.4.2 Web Crippling Strength of C-Section Webs With Holes ...................................................... 15Section C3.5.1 ................................................................................................................................................... 16Section C4 ......................................................................................................................................................... 16Section C6.1 ...................................................................................................................................................... 16Section C6.2 ...................................................................................................................................................... 16Section D3.2.1 ................................................................................................................................................... 16Section D3.3...................................................................................................................................................... 17Section E2.6 ...................................................................................................................................................... 17Section E2.7 ...................................................................................................................................................... 18

E2.7 Shear Lag Effect in Welded Connections of Members Other Than Flat Sheets ................... 18Section E3.2 ...................................................................................................................................................... 18

E3.2 Shear Lag Effect in Bolted Connections ............................................................................... 18Section E3.3 ...................................................................................................................................................... 20Section E5 ......................................................................................................................................................... 20

E5.2 Tension Rupture .................................................................................................................... 21E5.3 Block Shear Rupture.............................................................................................................. 21

Section E6.1 ...................................................................................................................................................... 21Section F1.......................................................................................................................................................... 21APPENDIX A: Base Test Method for Purlins Supporting a Standing Seam Roof System.............................. 23APPENDIX B: Standard Procedures for Panel and Anchor Structural Tests .................................................. 31


TABLE OF CONTENTS

COMMENTARY ON AISI 1996 SPECIFICATION FOR THE DESIGN OFCOLD-FORMED STEEL STRUCTURAL MEMBERS

SUPPLEMENT NO. 1

Section A3.1...................................................................................................................................................... 37Section A3.3...................................................................................................................................................... 37Section A7.1...................................................................................................................................................... 38Section A8......................................................................................................................................................... 38Section B2.4 ...................................................................................................................................................... 38

B2.4 C-Section Webs With Holes Under Stress Gradient ............................................................. 38Section B6.1 ...................................................................................................................................................... 39Section C2 ......................................................................................................................................................... 40

C2 Tension Members .................................................................................................................. 40Section C3.1.2 ................................................................................................................................................... 40

C3.1.2.1 Lateral-Torsional Buckling Strength for Open Cross Section Members............................... 40C3.1.2.2 Lateral-Torsional Buckling Strength for Closed Box Members............................................ 45

Section C3.1.3 ................................................................................................................................................... 45Section C3.1.4 ................................................................................................................................................... 45Section C3.1.5 ................................................................................................................................................... 46

C3.1.5 Strength for Standing Seam Roof Panel Systems.................................................................. 46Section C3.2 ...................................................................................................................................................... 47

C3.2.2 Shear Strength of C-Section Webs With Holes ..................................................................... 47Section C3.4 ...................................................................................................................................................... 47

C3.4.2 Web Crippling Strength of C-Section Webs With Holes ...................................................... 48Section C4 ......................................................................................................................................................... 48Section C6.1 ...................................................................................................................................................... 49Section C6.2 ...................................................................................................................................................... 49Section D3.2.1 ................................................................................................................................................... 49Section D3.3...................................................................................................................................................... 49Section E2 ......................................................................................................................................................... 50Section E2.6 ...................................................................................................................................................... 51Section E2.7 ...................................................................................................................................................... 51

E2.7 Shear Lag Effect in Welded Connections of Members Other Than Flat Sheets ................... 51Section E3.2 ...................................................................................................................................................... 51Section E3.3 ...................................................................................................................................................... 52Section E5 ......................................................................................................................................................... 53

E5 Fracture.................................................................................................................................. 53Section E6.1 ...................................................................................................................................................... 54Section F1.......................................................................................................................................................... 54Section F3.3....................................................................................................................................................... 54REFERENCES ................................................................................................................................................. 54


AISI 1996 SPECIFICATION FOR THE DESIGN OFCOLD-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, Cold-Rolled

ASTM A653/A653M (SS Grades 33, 37, 40, and 50 Class 1 and Class 3; HSLASTypes A and B, Grades 50, 60, 70 and 80), Steel Sheet, Zinc-Coated(Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-DipProcess

• Add ASTM A847 and ASTMA875/A875M to the section:

ASTM A847 Cold-Formed Welded and Seamless High Strength, Low AlloyStructural Tubing with Improved Atmospheric Corrosion Resistance

ASTM A875/A875M (SS Grades 33, 37, 40, and 50 Class 1 and Class 3; HSLASTypes A and B, Grades 50, 60, 70, and 80), Steel Sheet, Zinc-5% AluminumAlloy-Coated by the Hot-Dip Process

2. Section A3.3

• Move the first footnote on page V-26 to the Commentary (See Supplement to theCommentary for details).

• Revise Section A3.3.2 as follows:

A3.3.2 Steels conforming to ASTM A653 SS Grade 80, A611 Grade E, A792Grade 80, A875 SS Grade 80 and other steels which do not meet the provisionsof Section A3.3.1 shall be permitted for multiple-web configurations such asroofing, 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 yieldpoint 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 tensilestrength or 62 ksi (427 MPa), whichever is less.

Alternatively, the suitability of such steels for any configuration shall bedemonstrated by load tests according to the provisions of Section F1.Design strengths based on these tests shall not exceed the strengthscalculated according to Chapters B through E, using the specifiedminimum yield point, Fy, and the specified minimum tensile strength, Fu.

Exception: For multiple-web configurations, a reduced yield point, RbFy, shall


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 FlangesFor yFE067.0tw ≤

Rb = 1.0

For yy FE0.974twFE0.067 <<

Rb = 4.0y ]067.0)tE(wF[26.01 −− (Eq. A3.3.2-1)

For 500twFE974.0 y ≤≤Rb = 0.75

(b) Unstiffened Compression FlangesFor yFE0173.0tw ≤

Rb = 1.0

For 60twFE0.0173 y ≤<

Rb = )tE/(wF6.0079.1 y− (Eq. A3.3.2-2)

whereE = Modulus of elasticityFy = Yield point as specified in Section A7.1 ≤ 80 ksi (552 MPa)

t = Thickness of sectionw = Flat width of compression flange

The above Exception Clause does not apply to the use of steel deck forcomposite slabs, for which the steel deck acts as the tensile reinforcement of theslab.

3. Section A5.1.3

Revise the whole section as follows:

When the seismic load model specified by the applicable code or specification islimit state based, the resulting earthquake load (E) shall be permitted to be multipliedby 0.67. Additionally, except for Section D5, when the load combinations specifiedby the applicable code or specification or Section A5.1.2 include wind or earthquakeloads, 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”,


• 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 CorrosionResistance”,

• Add “ASTM A875/A875M-97 (SS Grades 33, 37, 40, and 50 Class 1 andClass 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”.

5. Section B1.1

Revise three conditions as follows:

(1) Stiffened compression element having one longitudinal edge connected to a webor flange element, the other stiffened by:

Simple lip 60Any other kind of stiffeneri) when Is < Ia 60

ii) when Is ≥ Ia 90

(2) Stiffened compression element with bothlongitudinal edges connected to otherstiffened 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


(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 DeterminationWhen 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 elementadjacent to the hole with f = f1 as shown in Figure B2.3-1.

(b) Deflection DeterminationThe effective widths shall be determined by Section B2.3(b) by assuming no holeexists 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 = Depth of flat portion of the web measured along the plane of the web

7. Section B6.1

Change “0.37” in the last paragraph to “0.42”.

8. Section C2


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 grosssection, (b) fracture in the net section away from connections, and (c) fracture in theeffective net section at the connection:(a) For yielding:

Tn = AgFy (Eq. C2-1)

Ωt = 1.67 (ASD)

φt = 0.90 (LRFD)

(b) For fracture away from the connection:Tn = AnFu (Eq. C2-2)

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


(c) For fracture at the connection:The nominal tensile strength shall also be limited by Sections E2.7, E3, and E4 fortension members using welded connections, bolted connections, and screwconnections, respectively.

9. 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 donot pass through the shear center of the cross section. See Section D3 for the design of lateral bracingrequired 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, andC3.1.2.2, Lateral-Torsional Buckling Strength for Closed Box Members. Section C3.1.2.1contains design provisions given in current Section C3.1.2 with revisions, and SectionC3.1.2.2 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-symmetricsections∗ subject to lateral-torsional buckling, the nominal flexural strength, Mn, shall

be calculated as follows:Mn ccFS= (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 Fcrelative 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 =

−

e

yy F36

F101F

9

10(Eq. C3.1.2.1-3)

For Fe ≤ 0.56FyFc = 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 includingmultiple-web deck, U- and closed box-type members, and curved or arch members). The provisions of this Section donot apply to laterally unbraced compression flanges of otherwise laterally stable sections. Refer to C3.1.3 for C- and Z-purlins in which the tension flange is attached to sheathing.


(a) For singly-, doubly-, and point-symmetric sections:

Fe = teyS

AorbC

fσσ for bending about the symmetry axis. (Eq. C3.1.2.1-5)

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 suchthat 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 doubly-

symmetric I-sections or point-symmetric sections.

For singly-symmetric sections bending about the centroidal axis perpendicularto the axis of symmetry:

Fe = ( )

σσ

σext

2o

2s

fTF

exs /r+jC+jSC

AC(Eq.C3.1.2.1-6)

Cs = +1 for moment causing compression on the shear center side of the centroid

Cs = -1 for moment causing tension on the shear center side of the centroid

σex = ( )π2

x x x2

E

K L / r(Eq. C3.1.2.1-7)

σey =( )

π2

y y y2

E

K L / r(Eq. C3.1.2.1-8)

σt =( )

π2

tt

w2

2o LK

EC+GJ

Ar

1(Eq. C3.1.2.1-9)

A = Full unreduced cross-sectional area

Cb =CBAmax

max3M+4M+3M+2.5M

12.5M(Eq. C3.1.2.1-10)

where:Mmax = Absolute value of maximum moment in 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

Cb is permitted to be conservatively taken as unity for all cases.

For cantilevers or overhangs where the free end is unbraced, Cbshall be taken as unity. For members subject to combinedcompressive axial load and bending moment (Section C5.2), Cbshall be taken as unity.

E = Modulus of elasticityCTF = 0.6 - 0.4 (M1/M2) (Eq. C3.1.2.1-11)

whereM1 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


sign (reverse curvature bending) and negative when they are ofopposite sign (single curvature bending). When the bendingmoment at any point within an unbraced length is larger than thatat both ends of this length, and for members subject to combinedcompressive axial load and bending moment (Section C5.2), CTFshall be taken as unity.

ro = Polar radius of gyration of the cross section about the shear center

= 2o

2y

2x x+r+r (Eq. C3.1.2.1-12)

rx, ry = Radii of gyration of the cross section about the centroidal principal axes

G = Shear modulusKx, 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 twistingxo = Distance from the shear center to the centroid along the principal x-axis, taken as

negativeJ = St. Venant torsion constant of the cross sectionCw = Torsional warping constant of the cross section

j = o2

A3

Ayx-dAxy+dAx

2I

1

∫∫ (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 =2

f

yc2

b

LS

EdIC π for doubly-symmetric I-sections (Eq. C3.1.2.1-14)

= 2

f

yc2

b

L2S

EdIC π for point-symmetric Z-sections (Eq. C3.1.2.1-15)

whered = Depth of sectionL = Unbraced length of memberIyc = 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 sectionOther 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

Lu = yfy

b EGJISF

0.36C π(Eq. C3.1.2.2-1)

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 lateralbuckling stress, Fe, is calculated as follows:


Fe = yEGJIfLS

bC π(Eq. C3.1.2.2-2)

whereL =Lateral unbraced length of memberIy =Moment of inertia of full unreduced section about its centroidal axis parallel to web

J = Torsional Constant of box sectionOther 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 betweeninflection 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 thecompression 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, andR = 0.60 for continuous span C-sections

= 0.70 for continuous span Z-sectionsSe and Fy are defined in Section C3.1.1.

The reduction factor, R, shall be limited to roof and wall systems meeting thefollowing 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 eachdirection (distance from center of support to end of lap) shall not be less than1.5 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 morethan 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 yieldstrength, and a minimum of 0.018 in. (0.46 mm) base metal thickness, having aminimum rib depth of 1-1/4 in. (32 mm), spaced a maximum of 12 in. (305mm) on centers and attached in a manner to effectively inhibit relativemovement between the panel and purlin flange

(11) Insulation shall be glass fiber blanket 0 to 6 inches (152mm) thick compressedbetween the member and panel in a manner consistent with the fastener being


used

(12)Fastener type: minimum No. 12 self-drilling or self-tapping sheet metal screwsor 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 andplaced 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 rationalanalysis procedure. In any case, the user is permitted to perform tests, in accordancewith Section F1, as an alternate to the procedure described in this section.

TABLE C3.1.3-1Simple 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 compressedinsulation between the sheeting and the member. The reduction shall be calculated bymultiplying R from Table 3.1.3-1 by the following correction factor, r:

r =1.00 - 0.01 ti when ti is in inches (Eq. C3.1.3-2)

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 firstparagraph.

• The “Base Test Method For Purlins Supporting a Standing Seam Roof System” isprovided in Appendix A, in which the base test procedure for members subjected touplift loads is included.

13. Section C3.1.5

The following is a new added section for the design of standing seam roof panelsystems. The “Standard Procedures for Panel and Anchor Structural Tests” is provided inAppendix 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 accordingto ASTM E1592-95 are to be evaluated, the Standard Procedures for Panel andAnchor Structural Tests of Part VIII of the AISI Cold-Formed Steel Design Manualshall 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 andresistance factors shall be determined in accordance with the procedures of Section


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

= 1.0Mm = Mean value of the material factor

= 1.1VM = 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

= 0.05VQ = Coefficient of variation of the load effect

= 0.21VP = 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), ornumber 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, of2.0 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 WebsWithout Holes, and C3.2.2, Shear Strength of C-Section Webs With Holes. Section C3.2.1contains the design provisions given in current Section C3.2 (Note, the equation numbers incurrent Section C3.2 need to be revised to “(Eq. C3.2.1-” accordingly), and Section C3.2.2 isa 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 ≥ 54qs = 1.0 (Eq. C3.2.2-1)

When 5 ≤ c/t < 54qs = c/(54t) (Eq. C3.2.2-3)

wherec = h/2 - d0/2.83 for circular holes (Eq. C3.2.2-4)

= h/2 - d0/2 for non-circular holes (Eq. C3.2.2-5)



b = Length of web holeh = 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 ofWebs 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 revisionsas 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)] (Eq. C3.4.1-2)

t2kC1C4C9Cθ[244 - 0.57(h/t)] [1 + 0.01(N/t)] (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 thebearing length:

Rc = 0.1hx083.0hd325.001.1 0 ≤+− (Eq. C3.4.2-1)

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:


Rc = 0.1hx053.0hd047.090.0 0 ≤+− (Eq. C3.4.2-2)

N ≥ 3 in. (76 mm)where

b = Length of web hole

d = Depth of cross section


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

Ωw = 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 shouldnot exceed 200, except that during construction only, KL/r preferably should not exceed300.” This recommendation is moved to the Commentary (See Supplement to theCommentary for details).

18. Section C6.1

Change “0.070” to “0.0714” and “0.319” to “0.318” both in the upper and the lowerlimits for D/t.

19. Section C6.2

Eqs. C6.2-5 and C6.2-6 are revised as follows:

Ae = )AA(RA 00 −+ (Eq. C6.2–5)

R = 0.1F2F ey ≤ (Eq. C6.2–6)

20. Section D3.2.1

• Replace the second and third sentences in the first paragraph with “If the top flangesof all purlins face in the same direction, anchorage of the restraint shall satisfy therequirements of Sections D3.2.1(a) and D3.2.1(b). If the top flanges of adjacentlines of purlins face in opposite directions, a restraint system shall be provided toresist 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:


(a) C-SectionsFor roof systems using C-sections for purlins with all compression flanges facingin the same direction, a system possessing restraint force, PL, in addition to

resisting other loading, shall be provided:PL = (0.05αcosθ - sinθ)W (Eq. D.3.2.1-1)

whereW= Total vertical load (nominal load for ASD, factored load for LRFD)

supported by all purlin lines being restrained. Where more than one brace isused at a purlin line, the restraint force PL shall be divided equally betweenall 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 negativevalue means that restraint is required to prevent movement of purlin flanges in thedownward 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 = 47.1t144 (Eq. E2.6-1)

For 0.14 in. ≤ t ≤ 0.18 in.:Pn = 43.4t + 1.93 (Eq. E2.6-2)

When t is in millimeters and Pn is in kN:

For 0.25 mm ≤ t < 3.56 mm:

Pn = 47.1t51.5 (Eq. E2.6-3)

For 3.56 mm ≤ t ≤ 4.57 mm:Pn = 7.6t + 8.57 (Eq. E2.6-4)

where t = Thickness of thinnest outside sheet.Ω = 2.50 (ASD)φ = 0.65 (LRFD)


23. Section E2.7


E2.7 Shear Lag Effect in Welded Connections of Members Other ThanFlat Sheets

The nominal tensile strength of a welded member shall be determined inaccordance with Section C2. For fracture and/or yielding in the effective net sectionof the connected part, the nominal tensile strength, Pn, shall be determined as follows:

Pn = AeFu (Eq. E2.7-1)

Ω = 2.50φ = 0.60Fu = 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 elementsU = 1.0

When the load is transmitted only by longitudinal welds or by longitudinalwelds in combination with transverse welds:

A = Gross area of member, AgU = 1.0 for members when the load is transmitted directly to all of the cross

sectional elements. Otherwise the reduction coefficient U isdetermined as follows:(a) For angle members:

U = 1.0 - 1.20 x L < 0.9 (Eq. E2.7-2)

but U shall not be less than 0.4.(b) For channel members

U = 1.0 - 0.36 x L < 0.9 (Eq. E2.7-3)

but U shall not be less than 0.5.

x = Distance from shear plane to centroid of the cross sectionL = 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 inaccordance with Section C2. For fracture and/or yielding in the effective net sectionof 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 (Eq. E3.2-2)

For double shear:Ω = 2.0 (ASD)φ = 0.65 (LRFD)


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 onlyone washer is provided under either the bolt head or the nut:

Ft = (1.0 - r + 2.5rd/s) Fu < Fu (Eq. E3.2-3)

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, dividedby the tension force in the member at that section. If r is less than 0.2, itshall be permitted to be taken as equal to zero.

s = Spacing of bolts perpendicular to line of stress; or gross width of sheetfor 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 = 2.22φ = 0.65

where

Ft is determined as follows:

(a) For connections when washers are provided under both the bolt head and the nut:Ft = (1.0 - 0.9r + 3rd/s) Fu ≤ Fu (Eq. E3.2-5)

(b) For connections when no washers are provided under the bolt head and thenut, or only one washer is provided under either the bolt head or the nut:Ft = (1.0 - r + 2.5rd/s) Fu ≤ Fu (Eq. E3.2-6)

An = 0.90 [Ag - nbdht + (∑s′2/4g)t] (Eq. E3.2-7)

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 holesg = Transverse center-to-center spacing between fastener gage linesnb = 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:

Pn = AeFu (Eq.E3.2-8)

Ω = 2.22φ = 0.65

where

Fu = Tensile strength of the connected part as specified in Section A3.1 or

A3.3.2


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 cross-sectional elements. Otherwise, the reduction coefficient U is determinedas follows:(a) For angle members having two or more bolts in the line of force

U = 1.0 - 1.20 x L < 0.9 (Eq. E3.2-9)

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 (Eq. E3.2-10)

but U shall not be less than 0.5.

x = Distance from shear plane to centroid of the cross sectionL = 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, thenominal 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)

AndΩ = 2.22φ = 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 ofbolted 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 E5.1contains the design provisions given in current Section E5, and Subsections E5.2, and E5.3are the new added sections. Changes to current Section E5 and the content of the newsections 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:


E5.2 Tension Rupture

The nominal tensile rupture strength along a path in the affected elements ofconnected members shall be determined by Section E2.7 or E3.2 for welded or boltedconnections, 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 < 0.6FuAnvRn = 0.6FuAnv + FyAgt (Eq. E5.3-2)

For bolted connections:Ω =2.22φ =0.65

For welded connections:Ω =2.50φ =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 steelcomponents covered by the Specification to adjacent structural components made ofother 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

…………

Structural Members Not Listed Above 1.00 0.10 1.00 0.05

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


Type of Component Mm VM Fm VF

…………

Connections Not Listed Above 1.10 0.10 1.00 0.15

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

APPENDIX A:

BASE TEST METHODFOR 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 nominalflexural strength of a purlin supporting a standing seam roof system. The reduction factor reflects theability of a particular standing seam roof system to provide lateral and rotational support to the purlins towhich it is attached. This applies to discrete lateral and torsional bracing when the sheeted flange of thepurlin is the compression flange, as in gravity loading cases, and when the unsheeted flange is thecompression flange, as in wind uplift cases.

1.2 This test method applies to an assembly consisting of the standing seam panel, purlin, andattachment devices used in the system being tested. The test specimen boundary conditions described inSection 6.6 apply only to standing seam roof systems for which the roof deck is positively anchored tothe 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 theirattachments, it is not practical to develop a generic method to predict the interaction of a particularstanding seam roof system and supporting structure. Therefore, the amount of resisting moment whichthe supporting purlins can achieve can vary from the fully braced condition to the unbraced condition fora given system.

1.4 This test method provides the designer with a means of establishing a nominal flexural strengthreduction factor for purlins in a simple span or continuous span, multiple purlin line, supporting astanding seam roof system, from the results of tests on a single-span, two-purlin line, sample of thesystem. The validity of this test method has been established by a research program at VirginiaPolytechnic 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 roofsubstructure

insulation - glass fiber blanket or rigid boardlateral - a direction normal to the span of the purlins in the plane of the roof sheetsthermal block - strips of rigid insulation located directly over the purlin between clipsnegative moment - a moment which causes tension in the purlin flange attached to the clips and

Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1-Appendix A 24

standing seam panelspan type standing seam roof - a "U" shaped panel which has vertical sidespositive moment - a moment which causes compression in the purlin flange attached to the clips and

standing seam panelsrib type standing seam roof - a panel which has ribs with sloping sides and forms a trapezoidal

shaped void at the side lapsliding clip - a hold down clip which allows the roof panel to move independently of the roof

substructurestanding 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 bymeans of concealed hold down clips that are attached to the purlins with mechanical fasteners

3.3 Symbols:

b = Flange width of the purlind = Depth of the purlinB = Purlin spacingFy = Design yield strength

Fyt = Measured yield strength of tested purlin

L = Span of the purlins tested, center to center of the supportsMn = Nominal flexural strength of a fully constrained beam, SeFy

minntM = Average flexural strength of the thinnest sections tested

maxntM = Average flexural strength of the thickest sections tested

Mnt = Flexural strength of a tested purlin, SetFyt

Mts = Failure moment for the single span purlins tested, wtsL2/8

pd = Weight of the specimen (force/area)

pts = Failure load (force/area) of the single span system tested

PL = Lateral anchorage force in accordance with Section D3.2.1 of the AISI Specification

Rt = Modification factor from test, Mts/MntR = Reduction factor computed for nominal purlin properties

mintR = Mean minus one standard deviation of the modification factors of the three thinnest

purlins tested

maxtR = Mean minus one standard deviation of the modification factors of the three thickest

purlins testeds = Tributary width of the purlins testedSe = Section modulus of the effective section

Set = Section modulus of the effective section of the tested member using measured

dimensions and the measured yield strengtht = Purlin thicknesswts = 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 C-and Z-sections used with standing seam roof systems. This procedure is referred to as the “Base TestMethod”. The method is the result of extensive testing of various combinations of purlins, standingseam panels, and fastening devices. The tests were conducted over several years, benefiting from the


experience provided by technical and industry experts. This procedure utilizes the results obtained fromsingle 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 C-and Z-sections of multi-span, multiple purlin line, standing seam systems, with or without discreteintermediate 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 systemexcept 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 isnecessary. A rectangular frame shall be constructed of any material with sufficient strength and rigidityto provide the desired pressure differential without collapse. A typical test chamber is shown on Figure1. Other chamber orientations shall be permitted.

DEFLECTION DIRECTIONS

SUPPORT BEAM

HORIZONTAL

VERTICAL

LONGITUDINAL

L3x3x1/4

L1x1x1/8

PURLINS

STANDING SEAM

PANELS

Figure 1 – Test Chamber

5.2 The length of the chamber shall be determined by the maximum length of the secondary members


as required by Section 7.2. The width of the chamber shall be determined by the maximum panel lengthas required by Section 6.9. Allowance shall be made in the interior chamber dimensions toaccommodate structural supports for the secondary members and sufficient clearance on all sides toprevent 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 insureadequate 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 thespecimen or its supports shall transfer the load to the frame support; the specimen, includingintermediate brace, shall not be attached to the chamber in any manner that would impede the deflectionof the specimen.

5.5 The test chamber shall be sealed against air leakage by applying 6 mil (0.15 mm) maximumthickness 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 toinhibit the spread of panel ribs under load. Edges of the polyethylene sheets shall be sealed against airleakage with tape or other suitable methods. Polyethylene sheets around the perimeter of the specimenshall 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 beinstalled to complete the coverage of the chamber opening. No attachment shall be made between thetest specimen and this supplemental coverage.

5.7 An air pump is necessary to create the pressure differential in the chamber. The pump shall be ofsufficient 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 toregulate the pressure differential in the chamber to ± 1 psf (0.05 kPa). This can be accomplished by (a) avariable 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 pumpconnection to the chamber is satisfactory.

5.9 A minimum of two pressure differential measuring devices shall be monitored throughout theduration 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 supportedand one of the frame end beams shall be sufficiently free to translate laterally to relieve any longitudinalcatenary forces in the specimen. Purlins shall be connected to the supporting beams as recommended inthe field erection drawings. Figure 1 shows the directional axes that are referred to in this testprocedure.

6.2 Panel supporting clips, fasteners, and panels shall be installed as recommended in the field erectiondrawings.

6.3 Means of providing restraint of purlins at the support shall be as required for use in actual fieldapplication, and shall be installed as recommended on the field erection drawings.


6.4 The purlins shall be arranged either with their flanges facing in the same direction or with theirflanges opposed. If the test is performed with the purlins opposed, and they are field installed with theirflanges 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 insuch 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 amember of compatible stiffness shall be attached to the underside at each end of the panels to preventseparation of the panels at the ends of the seam. Fasteners shall be placed on both sides of each majorrib. If the specimen is arranged with the purlin flanges facing in the same direction, a 3 in. x 3 in. (76mm x 76 mm) continuous angle with a maximum thickness of 1/4 in. (6 mm) or a member of compatiblestiffness shall be permitted to be substituted for the 1 in. x 1 in. (25 mm x 25 mm) angle at the end of thepanel, corresponding to the eave of the building using the standard panel to eave fastening system. (SeeFigure 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 bepermitted to be restrained against horizontal deflection at its ends as shown in Figure 1, providingvertical 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 fullengagement of the panel to purlin clip and attachment of the 1 in. x 1 in. (25 mm x 25 mm) angle at thepanel ends; but a length not greater than that required to achieve zero slope of the panel at the purlinsupport.

6.10 The spacing of purlins being tested shall not exceed the spacing typically used with the roofsystem. Results from this test shall be permitted to be used in designing purlins of the same profile thatare 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 ordimension other than thickness constitutes a change in profile. However, the lip dimension shall bepermitted to vary with section thickness consistent with the member design and not constitute a changein profile.

7.2 No fewer than six tests shall be run for each combination of purlin profile and panel system. Threetests shall be conducted with the thinnest purlin of the profile and three tests shall be conducted with thethickest purlin of the profile. All tests shall be conducted using the same purlin span which shall be thesame 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 usingcoupons taken from the web area of the failed purlin. Coupons shall not be taken from areas where cold-working stresses could affect the results.

7.4 For gravity loading, a pressure differential load shall be applied to the system to produce a positive


moment in the system. A positive moment is defined as one which causes compression in the purlinflange attached to the clips and standing seam panels. For uplift loading, a pressure differential loadshall be applied to the system to produce a negative moment in the system. A negative moment isdefined 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 beapplied 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 thespecimen will accept no further loading. The pressure differential at which the system fails shall berecorded as the failure load of the specimen. When the test must be stopped due to a flexural failure ofthe 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 deckdeflection in the horizontal direction shall be measured at the seam joint nearest the center of the testspecimen.

7.8 Deflections and pressures shall be recorded at pressure intervals equal to a maximum of 20 percentof 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 untilfailure occurs. The computation of the failure load, wts, is dependent on the purlin orientation for Z-

purlins 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 flangesof the purlins not restrained by anchorage to a point external to the panel/purlin system:

+

B

d2P + )sp (p = w Ldtsts

where

s)pp(td

b041.0P dts0.600.90

1.5

L +

=

For Z-purlins tested for gravity loading with flanges opposed and for C-sections tested for gravityloading:

)sp (p = w dtsts +

For Z-purlins or C-sections tested for uplift loading:

)sp (p = w dtsts −

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 ofthe purlin by the panel and resisted at the bottom flange of the purlin at the support. The expression2PL(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


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 sizeused in the test. The maximum allowable moment of a roof system purlin, simple span or continuous, islimited by the results of this test. The gravity load results apply for positive moment regions in the spanand 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 factorshall be determined from the following equation:

( ) 0.1RMMMM

RRR mintntn

ntnt

mintmaxtmin

minmax

≤+−

−−

=

where

mintR = 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 than1.0

maxtR = 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 than1.0

Mn = Nominal flexural strength of section for which R is being evaluated (SeFy)

minntM = Average flexural strength of the thinnest section tested, calculated in accordance with

Section 8.4

maxntM = 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, thediaphragm strength and stiffness of the panel system must be tested unless the purlins are also opposed


in actual field usage. The anchorage forces for the system braced in the manner tested shall becalculated in accordance with Section D3.2.1 of the AISI Specification. The diaphragm strength of thepanel 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 thanthe purlin span divided by 360 when subjected to the calculated brace force at the failure load of thepurlin.

9. Test Report

9.1 Documentation - The report shall include who performed the test and a brief description of thesystem being tested.

9.2 The documentation shall include test details with a drawing showing the test fixture and indicatingthe 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 materialspecifications 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 specimentype, 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 ofStanding Seam Roof Systems Under Gravity Loading,” MBMA Project 403, VPI Report No. CE/VPI-ST89/07, Metal Building Manufacturers Association, 1300 Sumner Ave., Cleveland, Ohio 44115, July1989, Revised November 1990.

(2) S. Brooks and T. Murray, "A Method for Determining the Strength of Z- and C-Purlin SupportedStanding Seam Roof Systems", Proceedings of the Tenth International Specialty Conference on Cold-Formed 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, 1300Sumner Ave., Cleveland, Ohio 44115, December 1990.

(4) T. Murray and B. Anderson, “Base Test Method for Standing Seam Roof Systems Subject to UpliftLoading - Phase I,” MBMA Project 501, VPI Report No. CE/VPI-ST90/06, Metal BuildingManufacturers Association, 1300 Sumner Ave., Cleveland, Ohio 44115, December 1990, RevisedDecember 1991.

(5) T. Murray and A. Pugh, “Base Test Method for Standing Seam Roof Systems Subject to UpliftLoading - Phase II,” MBMA Project 602, VPI Report No. CE/VPI-ST91/17, Metal BuildingManufacturers 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.

Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1-Appendix B 31

APPENDIX B:

STANDARD PROCEDURES FORPANEL AND ANCHOR STRUCTURAL TESTS

1. Scope

This procedure extends and provides methodology for interpretation of results of tests performedaccording 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 DifferenceA370-97 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 Terminology3.2.1 clip, a single or multiple element device that frequently attaches to one edge of a panel and isfastened 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 theintersection 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 sustainadditional loading.3.2.7 unlatching failure, disengagement of a panel seam or anchor that occurs in an unloaded assemblydue to permanent set or distortion that occurred when the assembly was loaded. This permanent set isnot always detectable from readings taken normal to the panel. It is deemed to be a serviceability failureuntil 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 panelsand/or their anchors under gravity or suction loading for use in a design procedure.

6. Test Apparatus


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

7. Safety Precautions


8. 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 panelin the field in any way. No additional structural attachments that would resist deflection of the field ofthe 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 Tests8.3.1 Tests shall use minimum thickness of support members (secondary structures) and maximumpanel span. If results are to be interpolated for other values, the other extremes must be tested in order tojustify an interpolation procedure.8.3.2 Tests shall be conducted to evaluate the field condition.

9. Calibration


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 inChapter F and Section C3.1.5 of the AISI Specification for the Design of Cold Formed Steel StructuralMembers.11.2 If a separate test series is performed to evaluate edge conditions and the results exceed the fieldcase by greater than one standard deviation, a separate design allowable is permitted to be established foredge conditions.11.3 A qualified design professional shall analyze deflections and permanent set data to assure thatdeflections 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 testresults. If the factor of safety is defined, report the allowable uniform design strength of the panelsystem. If the allowable design strengths of the panel and anchors are determined separately, they shallbe reported separately.12.3 If intermediate values are to be calculated for different spacings of anchors or secondarystructures, the basis of the interpolation shall be stated in the report. If the failure modes are different onany 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 ofdeflections and permanent set data at service loads.

Draft Version No. 1 of 1996 AISI Cold-Formed Steel Specification Supplement No. 1-Appendix B 33

COMMENTARY ON THE STANDARD PROCEDURES FORPANEL AND ANCHOR STRUCTURAL TESTS

1. Scope

The scope of the Procedure is for testing single skin panel systems. The procedure is based on ASTME1592-95 with specific additions to define the required safety factors for a design procedure. Edge stripdetail 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 usedin the development of this procedure.

3. Terminology

To promote accuracy and understanding, frequently used terms need mutual understanding. This listincludes 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 thebasis for a complete design procedure covering the evaluation of a safety factor for a range of productconfigurations. 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 toallow many facilities to perform tests. The size of the specimen is the most important criteria. Whetheror 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 failuremechanism. 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 thisprocedure.

8. Test Specimens

The size of a test specimen has been found to be an important element in demonstrating productperformance. Minimum sizes are defined, but larger sizes are allowed. It is understood that manyproducts are offered to the market that have insufficient usage to justify a large test program yet proof ofperformance to some degree is required. The procedure is developed to allow a single test with acorresponding penalty due to the reduced degree of demonstrated reliability with only a single test. Theprocedures of Section F provide for the reward/penalty relationship developed with increasing number oftests and the associated coefficient of variation.

Minimum specimen size is as required in ASTM E1592-95. The minimum specimen length of 24 ft. (7.3m) for the condition of constraint at both ends is consistent with the requirements of Factory MutualProcedure 4471 (1995). However, in the FM tests, panels are fastened down at all edges and it is termeda field test. The details of the FM test do not meet the ASTM E1592-95 tests in many conditions. Apurlin space of 5 ft. (1.5 m) requires 5 spans with both ends restrained. If one end is left free, the FM testwill meet E-1592-95. The application is also different in many cases because typically FM tests are run

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

with both ends restrained and this is used as a field test. Different results may be obtained when usingthe 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 afailed anchor instead of merely totaling the number of physical tests run on a complete assembly. Whentotaling 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 panelinstead 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 developedunder this procedure are intended to be used in a design procedure that encompasses different secondarystructural support spacings or thinner sections for anchors to attach to, the extremes must be tested inorder for interpolation to be valid. This precedent is established in the AISI Base Test Method forvalidating 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 withother existing and recognized standards. A significant difference between this procedure and the AISIBase 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 ofload versus deformation. Of paramount importance is the calculation of the resistance factor and safetyfactor of design strength or allowable design strength for panels and anchors. This procedure is anaddition to those required in ASTM E1592-95. If interpolation is to be a part of the resulting designprocess, 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.

COMMENTARYON THE 1996 EDITION OF THE

SPECIFICATIONFOR THE DESIGN OF

COLD-FORMEDSTEEL STRUCTURAL

MEMBERS

1996 EDITION

SUPPLEMENT NO. 1

American Iron and Steel Institute

36 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 SteelInstitute Committee on Specifications for the Design of Cold-Formed Steel StructuralMembers. The Committee has made a diligent effort to present accurate, reliable, and usefulinformation on cold-formed steel design. The Committee acknowledges and is grateful forthe contributions of the numerous researchers, engineers, and others who have contributed tothe body of knowledge on the subject. Specific references are included in the Supplement tothe Commentary on the Specification.

With anticipated improvements in understanding of the behavior of cold-formed steeland the continuing development of new technology, this material may eventually becomedated. It is anticipated that AISI will publish updates of this material as new informationbecome available, but this can not be guaranteed.

The materials set forth herein are for general information only. They are not a substitutefor competent professional advice. Application of this information to a specific projectshould be reviewed by a registered professional engineer. Indeed, in most jurisdictions, suchreview is required by law. Anyone making use of the information set forth herein does so attheir own risk and assumes any and all resulting liability arising therefrom.

1st Printing – April 2000

Produced by American Iron and Steel InstituteWashington, DC

Copyright American Iron and Steel Institute 2000

Draft Version No. 1 of Commentary on 1996 AISI Cold-Formed Steel Specification Supplement No. 1 37

COMMENTARY ON AISI 1996 SPECIFICATION FOR THE DESIGNOF COLD-FORMED STEEL STRUCTURAL MEMBERS

SUPPLEMENT NO. 1

JULY 30, 1999

1. 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 SSGrade 80 ……”, and

• Change “structural quality” in the last sentence to “SS”.

2. 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 “StandardMethods for Determination of Uniform and Local Ductility”, Cold-FormedSteel 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 thespecified minimum yield point, or 60 ksi (414 MPa), and the tensile strength used indesign 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 ductilitysteels, 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 determinethe 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 unstiffenedcompression 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 bendingstrength than previous editions of the AISI Specification. When the multiple-websection 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


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 oftests as permitted by the alternative method.

It should be noted that the Exception Clause does not apply to the steel deckused for composite slabs when the deck is used as the tensile reinforcement. Thislimitation is to prevent the possible sudden failure of the composite slab due to lack ofductility of the steel deck.

For the calculation of web crippling strength of deck panels, although the UMRstudy (Wu, Yu, and LaBoube, 1997) shows that the specified minimum yield pointcan be used to calculate the web crippling strength of deck panels, the Specification isadopting 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 strengthfor the low ductility steels. This is consistent with the previous edition of theSpecification.

Another UMR study (Koka, Yu, and LaBoube, 1997) confirmed that for theconnection design using SS Grade 80 of A653 steel, the tensile strength used in designshould be taken as 75 percent of the specified minimum tensile strength or 62 ksi (427MPa), whichever is less. It should be noted that the current AISI design provisions arelimited only to the design of members and connections subjected to static loadingwithout the considerations of fatigue strength.

3. Section A7.1

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

4. Section A8

Change “of” to “or” in condition 2.

5. Section B2.4


B2.4 C-Section Webs With Holes Under Stress Gradient

Studies of the behavior of web elements with holes conducted at the Universityof Missouri-Rolla(UMR) serve as the basis for the design recommendations forbending alone, shear, web crippling, combinations of bending and shear, and bendingand 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 onthe 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 standardweb holes. These holes were rectangular with fillet corners, punched during therolling process. For non-circular holes, the corner radii recommendation was adoptedto avoid the potential of high stress concentration at the corners of a hole. Webs withcircular holes and a stress gradient were not tested, however, the provisions areconservatively extended to cover this case. Other shaped holes must be evaluated bythe virtual hole method described below, by test, or by other provisions of theSpecification. The Specification is not intended to cover cross sections having


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 unstiffenedcompression element.

Although these provisions are based on tests of singly-symmetric C-sectionshaving the web hole centered at mid-depth of the section, the provisions may beconservatively applied to sections for which the full unreduced compression region ofthe web is less than the tension region. However, for cross sections having acompression region greater than the tension region, the web strength must bedetermined by test in accordance with Section F1.

The provisions for circular and non-circular holes also apply to any hole patternthat fits within an equivalent virtual hole. For example, Figure C-B2.4-1 illustratesthe 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 anallowed circular virtual hole. For each case, the design provisions apply to thegeometry 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 ysFE to 0.42 ysFE 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 samebasis for the stiffened and unstiffened elements of cold-formed steel transversestiffeners.


7. Section C2


C2 Tension Members

As described in Specification Section C2, the nominal tensile strength of axiallyloaded cold-formed steel tension members is determined either by yielding of thegross area of the cross-section or by fracture of the net area of the cross section. Atlocations of connections, the nominal tensile strength is also limited by the capacitiesspecified 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 thata tension member can achieve. The definition of yielding in the gross section todetermine the tensile strength is well established in hot-rolled steel construction.

For the LRFD Method, the resistance factor of φt = 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, Lateral-Torsional Buckling Strength for Open Cross Section Members, and C3.1.2.2, Lateral-Torsional Buckling Strength for Closed Box Members. The content of both subsections isprovided as follows:

C3.1.2.1Lateral-Torsional Buckling Strength for Open Cross SectionMembers

The bending capacity of flexural members is not only governed by the strengthof the cross section, but can also be limited by the lateral-torsional buckling strengthof the member if braces are not adequately provided. The design provisions fordetermining the nominal lateral-torsional buckling strength are given in SpecificationSection C3.1.2.1.

If a doubly-symmetric or singly-symmetric member in bending is laterallyunbraced, it can fail in lateral-torsional buckling. In the elastic range, the criticallateral-torsional buckling stress can be determined by Equation C-C3.1.2.1-1.

teyf

o2w

2

yf

cr S

Ar

GJL

EC1GJEI

LS= σσ=

π+πσ (C-C3.1.2.1-1)

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 theshear 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 theunbraced length.

For equal-flanged I-members, equation C-C3.1.2.1-2 can be used to calculatethe elastic critical buckling stress (Winter, 1947a; Yu, 1991):


2

2x

y2

x

y2

2

cr d

L

)I+2(1

JI+

2I

I

2(L/d)

E=

π

µ

πσ (C-C3.1.2.1-2)

In Equation C-C3.1.2.1-2, the first term under the square root represents thelateral bending rigidity of the member, and the second term represents the St. Venanttorsional rigidity. For thin-walled cold-formed steel sections, the first term usuallyexceeds the second term by a considerable margin.

For I-members with unequal flanges, the following equation has been derivedby Winter for the lateral-torsional buckling stress (Winter, 1943):

π

πσ2

y2

2

yytycf

2

2

crEdI

4GJL+1I+I-I

S2L

Ed= (C-C3.1.2.1-3)

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. Othersymbols 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-C3.1.2.1-4 by considering Iy = Iyc + Iyt and neglecting the term 4GJL2/π2IyEd2:

f2

yc2

crSL

EdI=

πσ (C-C3.1.2.1-4)

Equation C-C3.1.2.1-4 was derived on the basis of a uniform bending momentand 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.,

f2

yc2

be

SL

EdIC=F

π(C-C3.1.2.1-5)

where Cb is the bending coefficient, which can conservatively be taken as unity, or

calculated fromCb =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:

CBAmax

maxb 3M+4M+3M+2.5M

12.5M=C (C-C3.1.2.1-7)

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


for various shapes of moment diagrams within the unbraced segment. It gives moreaccurate solutions for fixed-end members in bending and moment diagrams which arenot straight lines. This equation is the same as that being used in the AISC LRFDSpecification (AISC, 1993).

Figure C-C3.1.2.1-1 shows the differences between Equations C-C3.1.2.1-6 andC-C3.1.2.1-7 for a straight line moment diagram.

< 2.3

2.0

Cb

1.5

1.0

0.5

2.5

+0.5+1.0 0 -0.5 -1.0

Cb

Cb

MA MB MC

M1M2

MA MB3 42.5M 3++ +

12.5M

max MC

max=

M1M2

M1M2

M1M2

= 1.75 + 1.05 + 0.32

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 toelastic buckling of cold-formed steel members in bending when the computedtheoretical buckling stress is less than or equal to the proportional limit. When thecomputed stress exceeds the proportional limit, the beam behavior will be governed byinelastic buckling. The inelastic buckling stress can be computed from Equation C-C3.1.2.1-8 (Yu, 1991):

−=

e

yyc F36

F101F

9

10F (C-C3.1.2.1-8)

The elastic and inelastic critical stresses for the lateral-torsional bucklingstrength 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.

y0.56

Fy

00

F

cF

Fy10

Lu Unbraced Length, L

9

C-Sections (1986 Specification)

I- and Z-sections (1986 Specification)

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


Equations C-C3.1.2.1-5 and C-C3.1.2.1-8 were used in the 1968, 1980 and 1986editions of the AISI Specification to develop the allowable stress design equations forlateral-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 thecritical moments, more design equations (Specification Equations C3.1.2.1-5 andC3.1.2.1-6) for elastic critical moment were added as alternative methods. Theseadditional equations were developed from the previous studies conducted by Pekoz,Winter and Celebi on torsional-flexural buckling of thin-walled sections undereccentric loads (Pekoz and Winter, 1969a; Pekoz and Celebi, 1969b) and are retainedin the 1996 and this edition of the Specification. These general design equations canbe used for singly-, doubly- and point-symmetric sections. It should be noted thatpoint-symmetric sections such as Z-sections with equal flanges will buckle laterally atlower strengths than doubly- and singly-symmetric sections. A conservative designapproach has been and is being used in the Specification, in which the elastic criticalbuckling stress is taken to be one-half of that for I-members.

Regarding the inelastic critical buckling stress, the following equation was usedfor calculating the critical moment in the 1986 edition of the Specification instead ofEquation C-C3.1.2.1-8 for singly-symmetric sections:

(Mcr)I =

−

ecr

yy )M(4

M1M (C-C3.1.2.1-9)

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 inSpecification Section C3.1.2.1(a) has been redefined to be consistent with the inelasticlateral buckling curve for I- or Z-sections in Specification Section C3.1.2.1(b). Thegeneral shape of the curve as represented by Equation C-C3.1.2.1-8 is also consistentwith the preceding edition of the Specification (AISI, 1980).

As specified in Specification Section C3.1.2.1, lateral-torsional buckling isconsidered 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 stressreduction due to lateral instability. This maximum unsupported length can becalculated 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 beam-columns (Pekoz and Sumer, 1992) and wall studs (Niu and Pekoz, 1994).

The above discussion dealt only with the lateral-torsional buckling strength oflocally stable beams. For locally unstable beams, the interaction of the local bucklingof the compression elements and overall lateral-torsional buckling of members mayresult in a reduction of the lateral-torsinal buckling strength of the member. The effectof local buckling on the critical moment is considered in Section C3.1.2.1 of the AISISpecification 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 Fcrelative to the extreme compression fiber

Using the above nominal lateral buckling strength with a resistance factor of


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 thatwhen the unbraced length is defined as the spacing between intermediate braces, theequations used in Specification Section C3.1.2.1 may be conservative for cases whereone mid-span brace is used, but may be unconservative where more than oneintermediate brace is used.

The above mentioned research (Ellifritt, Sputo, and Haynes, 1992) and the studyof 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 bucklingbetween braces, or by distortional buckling at or near the braced point. Thedistortional buckling strength of C- and Z-sections has been studied extensively at theUniversity 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 bucklingof I-members, channels, and Z-shaped sections for which the entire cross sectionrotates and deflects in the lateral direction as a unit. But this is not the case for U-shaped beams and the combined sheet-stiffener sections as shown in Figure C-C3.1.2.1-3. For this case, when the section is loaded in such a manner that the brimsand the flanges of stiffeners are in compression, the tension flange of the beamremains straight and does not displace laterally; only the compression flange tends tobuckle separately in the lateral direction, accompanied by out-of-plane bending of theweb, 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 BeamThe 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 onlylike a column on an elastic foundation, but the problem is also complicated by theweakening influence of the torsional action of the flange. For this reason, the designprocedure outlined in Section 2 of Part VII (Supplementary Information) of the AISICold-Formed Steel Design Manual (AISI, 1996) for determining the allowable designstrength for laterally unbraced compression flanges is based on the considerablesimplification of an analysis presented by Douty (1962).

In 1964, Haussler presented rigorous methods for determining the strength of


elastically stabilized beams (Haussler, 1964). In his methods, Haussler also treated theunbraced compression flange as a column on an elastic foundation and maintainedmore rigor in his development.

A comparison of Haussler’s method with Douty’s simplified method indicatesthat the latter may provide a lower value of critical stress.

An additional study of laterally unbraced compression flanges has been made atCornell University (Serrette and Pekoz, 1992, 1994 and 1995). An analyticalprocedure has been developed for determining the distortional buckling strength of thestanding seam roof panel. The predicted maximum capacities have been comparedwith 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-torsionalbuckling is not critical in typical design considerations, even for bending about themajor 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 lengthis 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, thewarping 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 SSRCGuide (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 beconservatively determined as follows:

Jab

a t b t=

+2 2

1 2

( )

( / ) ( / )(Eq. C-C3.1.2.2-1)

wherea = Distance between web centerlinesb = Distance between flange centerlinest1 = 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 Z-sections 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 byLaBoube……”.

10. Section C3.1.4

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


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 1996and 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 subsequentlyvalidated after further analysis of the research results.”

11. Section C3.1.5


C3.1.5 Strength of Standing Seam Roof Panel Systems

The nominal strength of a standing seam roof panel system is determined usingthe ASTM E1592-95 (1995) test procedure. A methodology of interpreting test resultsis specified in the Specification Section C3.1.5.

Clarification and extension of the ASTM E1592-95 (1995) test procedure ispresented in the Standard Procedures for Panel and Anchor Structural Tests in PartVIII of the AISI Cold-Formed Steel Design Manual. The Specification Section C3.1.5provides 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 strengthlimit/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 inSpecification Section C3.1.5 is not to set up guidelines to establish the serviceabilitylimit. The purpose is to define the method of determining the controlling allowableload whether based on the serviceability limit or on the ultimate load. The Corps ofEngineers Procedure CEGS 07416 (1991) requires a safety factor of 1.65 on strengthand 1.3 on serviceability. A buckling or crease does not have the same consequencesas a failure of a clip. In the latter case, the roof panel itself may become detached andexpose the contents of a building to the elements of the environment. Further,Galambos (1988) recommended a value of 2.0 for β0 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 (β0 = 2.5) are not nearly so

severe as the consequences of a primary frame connection failure (β0 = 3.5). The

intermittent nature of wind load as compared to the relatively long duration of snowload further justifies the use of β0 = 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 flexuralor other modes of failure. Section C3.1.5 also eliminates the limit on coefficient ofvariation 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 limitwill be beneficial when test results are consistent.

The value for the number of tests for fasteners is set as the number of anchorstested with the same tributary area as the anchor that failed. This is consistent withdesign practice where anchors are checked using a load calculated based on tributary


area. Actual anchor loads are not calculated from a stiffness analysis of the panel inordinary 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 thecontent of current Section C3.2 with revisions described below, and Section C3.2.2 is a newadded section as provided subsequently:

• Add subsection title “C3.2.1, Shear Strength of Webs Without Holes” after thesection title.

• Change the equation numbers in current Section C3.2 to “(C-C3.2.1-”, and revise thesection 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 webshear strength due to the presence of a web perforation. The test program considereda 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, wereconsidered in the test program. Eiler (1997) extended the work of Schuster and Shanfor the case of constant shear along the longitudinal axis of the perforation. He alsostudied linearly varying shear but this case is not included in the Specification. Thedevelopment 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 yv /FEk0.96h/t ≤ , an

anomaly exists; the calculated design shear strength is independent of t when h isconstant. In this region, the calculated design shear strength is valid but may besomewhat conservative.

The provisions for circular and non-circular holes also apply to any hole patternthat 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 thegeometry 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 WebsWithout 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 describedbelow, 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:


In the 1996 edition of the AISI Specification, HSLAS Grades 70 and 80 ofA653 and A715 steels were added in Specification Section A3.1. These two grades ofsteels have minimum yield points of 70 ksi (483 MPa) for grade 70 and 80 ksi (552MPa) for grade 80. Because the AISI provisions for web crippling strength werepreviously developed on the basis of the experimental investigations using steelshaving 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 Missouri-Rolla (Wu, Yu and LaBoube, 1997) indicated that the web crippling strengthincreased 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 designyield point for A653 SS Grade 80 and A611 Grade E steels is defined by SectionA3.3.2 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 webelement. These studies investigated both the end-one-flange and interior-one-flangeloading 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 bythe 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 patternthat 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 thegeometry 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 notexceed 200, except that during construction only, KL/r should not exceed 300. In1999, the above recommendations were moved from the Specification to theCommentary.

The maximum slenderness ratios on compression and tension members havebeen stipulated in steel design standards for many years but are not mandatory in theAISI Specification.

The KL/r limit of 300 is still recommended for most tension members in orderto control serviceability issues such as handling, sag and vibration. The limit is notmandatory, however, because there are a number of applications where it can beshown that such factors are not detrimental to the performance of the structure orassembly of which the member is a part. Flat strap tension bracing is a commonexample of an acceptable type of tension member where the KL/r limit of 300 is


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 strengthconcerns. The AISI Specification provisions adequately predict the capacities ofslender columns and beam-columns but the resulting strengths are quite small and themembers relatively inefficient. Slender members are also very sensitive toeccentrically applied axial load because the moment magnification factors given by1/α will be large.

15. Section C6.1

• In the third paragraph, after the second sentence add the sentence “In 1999, thebounds of Specification Equations C6.1-1 and C6.1-2 have been revised to provide anappropriate 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


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 = ey F2F 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 thesecond sentence of the second paragraph to “……Equations D3.2.1-2 throughD3.2.1-7……”.

• Add the following paragraph to the end of the section:

In 1999, an explicit requirement is indicated for purlins facing oppositedirections to resist the down-slope component of the total gravity load. To have aconsistent approach in calculating the restraint force for C- and Z-sections, EquationD3.2.1-1 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 andEquations D3.2.1-2 through D3.2.1-7 for Z-sections. The original research was doneassuming the roof was flat and the applied loading was parallel to the purlin webs. Inthe equations, Wcosθ is the component of the vertical loading parallel to the purlinwebs.

18. Section D3.3

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


19. Section E2

The following changes are made in response to the updates of the AWS StructuralWelding Code for Sheet Steel:

• Change the year of the recent edition of the AWS Structural Welding Code forSheet Steel to “(AWS, 1998)” referenced in the fourth paragraph and the sixthparagraph of Section E2.

• At the end of Section E2.1, add the sentence “Prequalified joint details are givenin AWS D1.3-98 (AWS, 1998).”

• At the end of Section E2.2, add the sentence “The provisions of Section E2.2 applyto 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 “Prequalifiedfillet 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 thegood 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 aprequalified weld in AWS D1.3-98 (AWS, 1998)……”.


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 strengthwhich replaces the tabulated values given in the previous specifications. The upperlimit of Eqs. E2.6-1 and E2.6-3 is selected to best fit the data provided in AWS C1.3-70, Table 2.1 and AWS C1.1-66, Table 1.3. Shear strength values for welds with thethickness of the thinnest outside sheet greater than 0.180 in. (4.57 mm) have beenexcluded in (Eq. E2.6-2) and (Eq. E2.6-4) due to the thickness limit set forth inSection E2.

21. Section E2.7

Add the following new sections:

E2.7 Shear Lag Effect in Welded Connections of Members Other ThanFlat Sheets

Shear lag has a debilitating effect on the nominal tensile strength of a crosssection. The AISI Specification addresses the shear lag effect on tension membersother than flat sheets in welded connections. The AISC Specification’s designapproach has been adopted.

When computing U for combinations of longitudinal and transverse welds, L istaken 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 planeto 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……”.


• Add the following paragraphs to the end of the section:

The presence of staggered or diagonal hole patterns in a bolted connectionhas long been recognized as increasing the net section area for the limit state offracture in the net section. LaBoube and Yu (1995) summarized the findings of alimited 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 afracture plane can be adjusted by use of s′2/4g.

Because of the lack of test data necessary for a more accurate designformulation, a discontinuity between AISI and AISC cannot be avoided. The presenceof a discontinuity should not be a significant design issue because the use of thestaggered 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 beendeveloped that can be used to estimate the influence of the shear lag. The researchdemonstrated that the shear lag effect differs for an angle and a channel. For bothcross sections, however, the key parameters that influence shear lag are the distancefrom the shear plane to the center of gravity of the cross section and the length of thebolted 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 φused 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 holeelongation prior to reaching the limited bearing strength of a bolted connection. Theresearchers adopted an elongation of 0.25 in. (6.4 mm) as the acceptable deformationlimit. This limit is consistent with the permitted elongation prescribed for hot-rolledsteel.

Research at the University of Sydney (Rogers and Hancock, 1998), hasshown 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 thereforebeen chosen for Table E3.3-1.


24. Section E5


E5 Fracture

Connection tests conducted by Birkemoe and Gilmor (1978) have shown that oncoped beams a tearing failure mode as shown in Figure C-E5-1(a) can occur along theperimeter of the holes. Hardash and Bjorhovde (1985) have demonstrated theseeffects 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 beenadopted from the AISC Specification (AISC, 1978). For additional design informationon tension rupture strength and block shear rupture strength of connections (FiguresC-E5-1 and C-E5-2), refer to the AISC Specifications (AISC, 1989 and 1993).

Sheararea

Cope

Tensilearea

Failure by tearingout of shadedportion Shear

area

Beam

Tensilearea

Po

Failure by tearingout of shadedportion

(a) (b)

Large shearforce

Po

Po

Small tensionforce

(a) (b)

Small shearforce

Po

Po

Large tensionforce

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

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

Figure C-E5-2 Block Shear Rupture in Tension


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


The design provisions for the nominal bearing strength on the other materialsshould be derived from appropriate material specifications.

26. Section F1


In 1999, two entries were added to Table F1, one for "Structural Members NotListed Above" and the other for "Connections Not Listed Above". It was considerednecessary to include these values for members and connections not covered by one ofthe existing classifications. The statistical values were taken as the most conservativevalues 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 StructuralPerformance of Sheet Metal Roof and Siding Systems by Uniform Static Air PressureDifference,” E 1592-95, 1995.

American Society for Testing and Materials (1997), “Standard Methods andDefinitions 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 WebOpenings Subjected to Web Crippling and a Combination of Bending and WebCrippling for Interior-One-Flange Loading," thesis presented to the faculty of theUniversity of Missouri-Rolla in partial fulfillment for the degree Master of Science.


Eiler, M. R., LaBoube, R. A., and Yu, W.W. (1997), “Behavior of Web Elementswith Openings Subjected to Linearly Varying Shear,” Final Report, CivilEngineering Series 97-5, Cold-Formed Steel Series, Department of CivilEngineering, University of Missouri-Rolla

Fisher, J. M., (1996), “Uplift Capacity of Simple Span Cee and Zee Members withThrough - Fastened Roof Panels,” Final Report MBMA 95-01, Metal BuildingManufacturers 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. 88-06published by AISI, 1988.

Hardash, S. G., and Bjorhovde, R. (1985), “New Design Criteria for Gusset Plates inTension,” AISC Engineering Journal, Vol. 22, No. 2, 2nd Quarter.

Koka, E.N., W. W. Yu and R. A. LaBoube (1997), “Screw and Welded ConnectionBehavior Using Structural Grade 80 of A653 Steel (A Preliminary Study),” FourthProgress 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 BoltedConnections,” Final Summary Report, Civil Engineering Study 95-6, Cold-FormedSteel Series, Department of Civil Engineering, University of Missouri-Rolla.

Langan, J. E., LaBoube, R. A., and Yu, W. W. (1994), "Structural Behavior ofPerforated Web Elements of Cold-Formed Steel Flexural Members Subjected to WebCrippling and a Combination of Web Crippling and Bending," Final Report, CivilEngineering Series 94-3, Cold-Formed Steel Series, Department of CivilEngineering, University of Missouri-Rolla

Pan, L.C., and W. W. Yu (1988), "High Strength Steel Members with UnstiffenedCompression Elements," Proceedings of the Ninth International SpecialtyConference on Cold-Formed Steel Structures, University of Missouri-Rolla, MO,November, 1988.

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Shan, M. Y., LaBoube, R. A., and Yu, W. W. (1994), "Behavior of Web Elementswith Openings Subjected to Bending, Shear and the Combination of Bending andShear," 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-FormedSteel Perforated C-Sections in Shear," Progress Report No. 1 of Phase I ofCSSBI/IRAP Project, Department of Civil Engineering, University of Waterloo,Waterloo, Ontario Canada

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Uphoff, C. A. (1996), "Structural Behavior of Circular Holes in Web Elements ofCold-Formed Steel Flexural Members Subjected to Web Crippling for End-One-Flange Loading," thesis presented to the faculty of the University of Missouri-Rollain partial fulfillment for the degree Master of Science.


Wu, S., W. W. Yu and R. A. LaBoube (1996), “Strength of Flexural Members UsingStructural Grade 80 of A653 Steel (Deck Panel Tests),” Second Progress Report,Civil Engineering Study 96-4, University of Missouri-Rolla, Rolla, MO, November1996.

Wu, S., W. W. Yu and R. A. LaBoube (1997), “Strength of Flexural Members UsingStructural Grade 80 of A653 Steel (Web Crippling Tests),” Third Progress Report,Civil Engineering Study 97-3, University of Missouri-Rolla, Rolla, MO, February1997.


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