Steel Buildings in Europe

Part 4: Detailed Design of Portal Frames 4 - 76 APPENDIX C Determination of M CR and N cr C.1 M cr for uniform members C.1.1 General expression The method given in C.1.1 only applies to uniform straight members for which the cross-section is symmetric about the bending plane.                         2 g 2 2 g z 2 t 2 z w 2 w 2 z 2 1 cr C z C z EI GI kL I I k k kL EI M C   In the case of a portal frame, k = 1 and k w = 1. The transverse load is assumed to be applied at the shear centre and therefore C 2 z g = 0. The expression may be simplified to: z 2 t 2 z w 2 z 2 1 cr EI L GI I I L EI M C     E is Young modulus (E = 210000 N/mm 2 ) G is the shear modulus (G = 81000 N/mm 2 ) I z is the second moment of area about the weak axis I t is the torsional constant I w is the warping constant L is the beam length between points of lateral restraint C 1 depends on the shape of the bending moment diagram C.1.2 C 1 factor The factor C 1 may be determined from Table C.1 for a member with end moment loading, and also for members with intermediate transverse loading.