AISC LRFD 1.pdf

96App. FAPPENDIX FBEAMS AND OTHER FLEXURAL MEMBERSAppendix F1 provides the design flexural strength of beams and other flexural members.Appendix F2 provides the design shear strength of webs with and without stiffeners andrequirements on transverse stiffeners. Appendix F3 applies to web-tapered members.F1. DESIGN FOR FLEXUREThe design strength for flexural members is b M n where b = 0.90 and M n is the nominalstrength.Table A-F1.1 provides a tabular summary of Equations F1-1 through F1-15 fordetermining the nominal flexural strength of beams and other flexural members.For slenderness parameters of cross sections not included in Table A-F1.1, seeAppendix B5.3. For flexural members with unequal flanges see Appendix B5.1 forthe determination of r for the limit state of web local buckling.The nominal flexural strength M n is the lowest value obtained according to the limitstates of yielding: lateral-torsional buckling (LTB); flange local buckling (FLB);and web local buckling (WLB).The nominal flexural strength M n shall be determined as follows for each limit state:(a) For l £ l p :Mn= M p(A-F1-1)(b) For l p < l £ lr:For the limit state of lateral-torsional buckling:éæ l - l öùM C M M M Mêëúûpn=b ê p-( p-r)ç ú£plrl÷è -pøFor the limit states of flange and web local buckling:(A-F1-2)pM (A-F1-3)nMp ( Mp Mr) æ l - l= - - öç ÷èlr- lpø(c) For l > l r :For the limit state of lateral-torsional buckling and flange local buckling:M n = M cr = SFcr £ M p(A-F1-4)LRFD Specification for Structural Steel Buildings, December 27, 1999AMERICAN INSTITUTE OF STEEL CONSTRUCTION