AISC LRFD 1.pdf

App. F3.] WEB-TAPERED MEMBERS 105Fwg =5.9E( hL/ r )wTo2(A-F3-7)whereh s = factor equal to10 . + 0. 230g Ld / Aoh w = factor equal to10 . + 0. 00385g L/r Tor To = radius of gyration of a section at the smaller end, considering only thecompression flange plus one-third of the compression web area, taken aboutan axis in the plane of the web, in. (mm)A f = area of the compression flange, in. 2 (mm 2 )and where B is determined as follows:(a) When the maximum moment M 2 in three adjacent segments of approximatelyequal unbraced length is located within the central segment and M 1 is the largermoment at one end of the three-segment portion of a member:fæ M ö æ1M ö1B = 1.0 + 0.37ç 1.0 + + 0.50g1.0 + ³ 1.0è M ÷øçè M ÷ø2 2(A-F3-8)(b) When the largest computed bending stress f b2 occurs at the larger end of twoadjacent segments of approximately equal unbraced lengths and f b1 is the computedbending stress at the smaller end of the two-segment portion of a member:æ f ö æ f öB = +ç+ - + ³è f ÷øçè f ÷øb1 b11.0 0.58 1.0 0.70g1.0 1.0b2 b2(A-F3-9)(c) When the largest computed bending stress f b2 occurs at the smaller end of twoadjacent segments of approximately equal unbraced length and f b1 is the computedbending stress at the larger end of the two-segment portion of a member:æ f ö æ f öB = +ç+ + + ³è f ÷øçè f ÷øb1 b11.0 0.55 1.0 2.20g1.0 1.0b2 b2(A-F3-10)In the foregoing, =(d L -d o )/d o is calculated for the unbraced length that containsthe maximum computed bending stress. M 1 /M 2 is considered as negative whenproducing single curvature. In the rare case where M 1 /M 2 is positive, it is recommendedthat it be taken as zero. f b1 /f b2 is considered as negative when producingsingle curvature. If a point of contraflexure occurs in one of two adjacent unbracedsegments, f b1 /f b2 is considered as positive. The ratio f b1 /f b2 0.(d) When the computed bending stress at the smaller end of a tapered member orsegment thereof is equal to zero:LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION