Lateral buckling strengths of cold-formed Z-section beams

This paper is concerned with the inelastic lateral buckling strengths of co ld-formed Z-section (CFZ) beams. The point symmetry of the cross-section of a CFZ beam introduces characteristics that are not encountered in a doubly symmetric I-beam. Firstly, the effective section rotates after yielding, s o that a CFZ beam under in-plane bending about the geometrical major princi pal axis is subjected to bending moments about the effective minor axis and bimoments. Secondly, the minor axis bending and warping strain distributio ns and therefore the lateral inelastic buckling behaviour and strengths of CFZ beams are related to the twist rotation and minor axis displacement dir ections. The stress-strain curves, residual stresses, initial imperfections , and lipped flanges of CFZ beams are all different to those of hot-rolled I-beams. This paper develops a realistic finite element model for the analy sis of CFZ beams and uses it to investigate the elastic lateral-distortiona l buckling, inelastic behaviour, and strengths of CFZ beams with residual s tresses and initial imperfections. The results of the study are used to dev elop improved design rules which are suitable for CFZ beams. The effects of moment distribution and load height on the lateral buckling strengths are also studied. (C) 1999 Elsevier Science Ltd. All rights reserved.