Experimental and numerical investigation of shear buckling behaviour of friction stir welded 6013-T6 aluminium H-shaped beams

Friction stir welding (FSW) facilitates the fabrication of aluminium alloy H-shaped beams, with thin webs for lightweight bridge and building structures, however, the shear buckling behaviour of such members and appropriate design rules remain insufficiently characterized. Six FSW 6013-T6 aluminium alloy H-shaped beams were tested under shear-dominated loading, with variations in weld configuration and end restraint conditions. The shear buckling modes, tension-field development, load-displacement responses and ultimate shear buckling bearing capacities were comprehensively recorded. The refined finite element (FE) models, incorporating FSW softening, residual stresses and initial geometric imperfections, were developed and validated against experimental results. A parametric study involving 798 models was then performed to quantify the effects of web slenderness, web aspect ratio, weld properties (strength, width and location) and end restraint on post-buckling shear resistances. The combined test and numerical database were used to evaluate the shear design provisions in EN 1999–1–1:2023 and ADM 2020, which were found to yield conservative predictions by over 26.6–42.2%, with increasing scatter at higher web slenderness. To improve design accuracy while retaining the existing code framework, modified shear design formulations were proposed for both EN 1999–1–1 and ADM 2020, and a dedicated shear design curve was developed within the direct strength method (DSM) framework. The modified test/FE-to-prediction ratios concentrated within the range of 1.002–1.202, with COVs of 0.05–0.18, providing a rational basis for the design and potential codification of FSW 6 × ×× -series aluminium alloy structural members.