Tension-Flange Restraint Effect on Lateral-Torsional Buckling Moment Capacity of Web-Tapered Steel I-Sections

Abstract

The web-tapered beams have advantages above the conventional rolled I-sections. They combine economy, efficiency, and aesthetics, especially with flange lateral restraint. In this paper, the effect of tension flange restraint on the lateral-torsional buckling (LTB) moment capacity is investigated numerically using finite element analysis. ABAQUS software is used to construct a finite element model (FEM) which is verified against available experimental results in the literature. A parametric study is carried out using different parameters: tapering ratio, beam length, moment gradient, and cross-section properties. FEM results are compared to the latest AISC Design Guide No.25. The restraint at the tension flange enhances the moment capacity, especially for beams with narrow flanges and long spans. One restraint at the mid-span is found to be adequate. The gain in capacity is more noticeable for gradient moment rather than uniform moment. A design procedure is proposed by considering a factor to the available rules to account for the advantage of tension flange restraint. The proposed equation of the enhancement factor is found to be accurate compared to the FEM.