Flexural distortional strength of steel beams determined by finite-element modelling

Abstract

This paper reports on the development of a three-dimensional finite-element model for inelastic non-linear flexural buckling analysis of steel I-beams. The model was used to investigate the effects of unbraced length and yield strength on member moment capacity. Unlike existing design codes, the model considers the effect of web distortions in a lateral-distortional buckling mode. Beam slenderness ranges can be divided into three main regions depending on the failure type – low slenderness (plastic), intermediate slenderness (inelastic buckling) and high slenderness (elastic buckling). Structural design codes give criteria that specify some form of transition from the end of the elastic region to the plastic moment. In the work reported in this paper, the effect of yield strength and web distortion on the limiting laterally unbraced length for the limit state of inelastic lateral-torsional buckling (LTB) was investigated. The numerical beam strengths were compared with the design strengths predicted by current design codes, specifically the load and resistance factor design (LRFD) of the American Institute of Steel Construction (AISC), Australian Standard AS 4100 and BS EN 1993-1-2.