AISC LRFD 1.pdf

90 LOCAL BUCKLING [App. B5.3a. Unstiffened Compression ElementsThe design strength of unstiffened compression elements whose width-thicknessratio exceeds the applicable limit r as stipulated in Section B5.1 shall be subject toa reduction factor Q s . The value of Q s shall be determined by Equations A-B5-3through A-B5-10, as applicable. When such elements comprise the compressionflange of a flexural member, the design flexural strength, in ksi, shall be computedusing b F y Q s , where b = 0.90. The design strength of axially loaded compressionmembers shall be modified by the appropriate reduction factor Q, as provided inAppendix B5.3d.(a) For single angles:when0.45 E/ F < b/ t < 0.91 E/ F :yyQ = 1.340 -0.76( b/ t) F / Esy(A-B5-3)Errata 9/4/01whenb/ t > 0.91 E/ F y:( )Qs= 0.53 E/ éFyb/t 2 ùë û(A-B5-4)(b) For flanges, angles, and plates projecting from rolled beams or columns orother compression members:when 0.56 E/ F < b/ t < 1.03 E/ F :yyQ = 1.415 -0.74( b/ t) F / Esy(A-B5-5)whenb/ t ³ 1.03 E/ F y:( )Qs= 0.69 E/ éFyb/t 2 ùë û(A-B5-6)(c) For flanges, angles and plates projecting from built-up columns or other compressionmembers:when 0.64 E/( F / k ) < b/ t < 1.17 E/( F / k ) :y c y cQ = 1.415 -0.65( b/ t) ( F / k E)s y c(A-B5-7)whenb/ t ³ 1.17 E/( F / k ):yc( )Qs = 0.90 Ekc / éFyb/t 2 ùë û(A-B5-8)The coefficient, k c , shall be computed as follows:(a) For I-shaped sections:LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION