Numerical assessment of lateral-torsional buckling in high-strength steel welded I-beams

Lateral-torsional buckling (LTB) is a critical limit state for welded high-strength steel (HSS) I-beams, especially when slender plates, residual stresses, geometric imperfections, and destabilizing load positions are present. This study investigates the LTB behaviour of welded HSS I-beams through finite element models developed in Abaqus using Linear Buckling Analysis and Geometrically and Materially Nonlinear Analysis with Imperfections. The models were validated against experimental results for Q460/S460 and S690 homogeneous and hybrid welded beams. A parametric study covering S355, S460, S690, and S960 steels, different unbraced lengths, and five loading configurations was conducted. Numerical resistances were compared with ANSI/AISC 360–22, BS EN 1993–1–1:2022, and AS 4100:2020. The results show that the benefits of HSS depend strongly on member slenderness, moment distribution, and load application position. Higher steel grades were more effective for compact and moderately slender beams, whereas their advantages decreased when lateral-torsional or local–global instability governed. The comparisons also indicate the need for further calibration of current design provisions for slender welded HSS beams subjected to destabilizing transverse loads.