Member Strength by Inelastic Lateral Buckling (No. R824)

Abstract

This paper develops a simple advanced method of designing steel members against out-of-plane failure, in which reduced elastic moduli are used in an out-of-plane buckling analysis to model the effects of high moment, residual stresses and geometrical imperfections on yielding. The reduced moduli are derived from the basic beam and column strength curves of the Australian steel code AS4100 (SA, 1998). The strengths predicted for simply supported beams in uniform bending are exactly the same as those of AS4100, while those for simply supported columns are extremely close. The strengths predicted for simply supported beam-columns with equal and opposite end moments are a little higher than the less conservative predictions of AS4100, and are very close to the basic beam and column strengths when these are plotted against a consistent generalized slenderness. The strengths predicted for simply supported beams under double curvature bending are somewhat less than those of the AS4100 method of design by buckling analysis, while those for beams with central concentrated loads acting at or away from the shear centre are very close, and those for end restrained beams under uniform bending and for sway columns are generally a little higher. While the method has been developed from and compared with the Australian code AS4100, it may be modified for any other modern code for the design of steel structures. It may be more widely applied to two-dimensional frames with in-plane loading, as part of a simple method of advanced analysis in which separate assessments are made of the in-plane and out-of plane strengths.