LATERAL BUCKLING STRENGTHS OF COLD-FORMED RECTANGULAR HOLLOW SECTIONS

Cone rules for designing steel beams against lateral buckling which ar e based on data for hot-rolled I-sections are unnecessarily conservati ve when used for cold-formed rectangular hollow section beams. Cold-fo rmed rectangular hollow section beams have different stress-strain cur ves, residual stresses, and crookedness and twist. The effects of resi dual stress on the inelastic buckling of I-section beams are not nearl y as pronounced for hollow sections with two webs, while the strengthe ning effects of pre-buckling deflections are greater for hollow sectio ns. Simplistic code rules for top flange loading are very conservative where applied to hollow sections. This paper reviews elastic lateral buckling behaviour and the strength rules used to design steel beams. It develops realistic models for cold-formed rectangular hollow beams which are analysed to pr edict the effects of moment distribution, loa d height and yield stress on their strengths. The results of the analy ses are used to develop improved design rules which remove much of the conservatism of present design rules.