Buckling of high-strength steel members

High-strength steel (HSS) with a yield strength over 450 MPa is gaining increasing use in modern building construction, but there is little guidance available in current design standards. This research uses an accurate and reliable finite element (FE) model to investigate the buckling strengths and failure modes of HSS beams and, based on the results of the study, it proposes corresponding strength design criteria. The study involves both a uniform and web-tapered I-section beam with simply supported boundary conditions and subjected to a pair of end moments. The FE model is developed with using the commercial software ABAQUS, incorporating the non-linear material characteristics and residual stresses as measured experimentally in the open literature, and the initial geometric imperfections in accordance with design standards. The accuracy of the numerical model is verified against several experimental results. The validated FE model is applied to investigate the influences of the changes in different parametric factors on the buckling moment capacities of HSS members considering local buckling, flexural-torsional buckling, and their interaction. The parameters include the span length, the section dimensions, the steel grades, the taper ratios, and the end moment ratios. It is demonstrated that the buckling strengths are primarily related to the proposed generalised slenderness and section slenderness. In the design proposal, the applicability of the design formulations given in current design codes for predicting the buckling moment capacities of HSS beams is assessed by comparing the results with those obtained from the FE analysis. The result shows that the current design rules of AS4100 and EC3 appear to underestimate the moment capacities of HSS beams, as they have different yield and post-yield characteristics and patterns of residual stresses from mild steel beams. Accordingly, a set of new strength design equations are proposed from the numerical data, based on the generalised and section slenderness, ...