AISC LRFD 1.pdf

App. F1.] DESIGN FOR FLEXURE 97For the design of other flexural members with slender webs, the limit state of weblocal buckling is not applicable. See Appendix G2.For of the flange > r in shapes not included in Table A-F1.1, see Appendix B5.3.For l of the web > r , see Appendix G.The terms used in the above equations are:M n = nominal flexural strength, kip-in. (N-mm)M p = F y Z, plastic moment 1.5 F y S, kip-in. (N-mm)M cr = buckling moment, kip-in. (N-mm)M r = limiting buckling moment (equal to M cr when = r ), kip-in. (N-mm) = controlling slenderness parameter= minor axis slenderness ratio L b / r y for lateral-torsional buckling= flange width-thickness ratio b/tfor flange local buckling as defined in SectionB5.1= web depth-thickness ratio h/t w for web local buckling as defined in SectionB5.1 p = largest value of for which M n = M p= largest value of for which buckling is inelastic rF crC b= critical stress, ksi (MPa)= bending coefficient dependent on moment gradient, see Section F1.2a,Equation F1-3S = section modulus, in. 3 (mm 3 )L br y= laterally unbraced length, in. (mm)= radius of gyration about minor axis, in. (mm)The applicable limit states and equations for M p , M r , F cr , , p , and r are given in theTable A-F1.1 for shapes covered in this Appendix. The terms used in the table are:A = cross-sectional area, in. 2 (mm 2 )F LF rF yF yf= smaller of (F yf – F r ) or F yw , ksi (MPa)= compressive residual stress in flange= 10 ksi (69 N/mm 2 ) for rolled shapes= 16.5 ksi (114 N/mm 2 ) for welded shapes= specified minimum yield strength, ksi (MPa)= yield strength of the flange, ksi (MPa)F yw = yield strength of the web, ksi (MPa)I yc = moment of inertia of compression flange about y axis or if reverse curvaturebending, moment of inertia of smaller flange, in. 4 (mm 4 )J = torsional constant, in. 4 (mm 4 )R e= see Appendix G2S eff = effective section modulus about major axis, in. 3 (mm 3 )S xc = section modulus of the outside fiber of the compression flange,in. 3 (mm 3 )S xt = section modulus of the outside fiber of the tension flange, in. 3 (mm 3 )Z = plastic section modulus, in. 3 (mm 3 )bdf= flange width, in. (mm)= overall depth, in. (mm)= computed compressive stress in the stiffened element, ksi (MPa)LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION