AISC LRFD 1.pdf

182 LOCAL BUCKLING [Comm. B5.earlier editions of both the ASD and LRFD Specifications. An h/t w = 27.5 isrequired to reach k c = 0.763. Fully fixed restraint for an unstiffened compressionelement corresponds to k c = 1.3 while zero restraint gives k c = 0.42. Because ofweb-flange interactions it is possible to get k c 0.42 from the new k c formula. Ifh/ t w 570 . E/F y use h/t w =570 . E/F y in the k c equation, which correspondsto the 0.35 limit.Illustrations of some of the requirements of Table B5.1 are shown in Figure C-B5.1.B7. LIMITING SLENDERNESS RATIOSChapters D and E provide reliable criteria for resistance of axially loaded membersbased on theory and confirmed by tests for all significant parameters includingslenderness. The advisory upper limits on slenderness contained in Section B7 arebased on professional judgment and practical considerations of economics, ease ofhandling, and care required to minimize inadvertent damage during fabrication,transport, and erection. Out-of-straightness within reasonable tolerances does notaffect the strength of tension members, and the effect of out-of-straightness withinspecified tolerances on the strength of compression members is accounted for informulas for resistance. Applied tension tends to reduce, whereas compressiontends to amplify, out-of-straightness. Therefore, more liberal criteria are suggestedfor tension members, including those subject to small compressive forces resultingfrom transient loads such as earthquake and wind. For members with slendernessratios greater than 200, these compressive forces correspond to c F cr less than 5.33ksi (18 MPa).LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION