Thin‐Walled Steel Box Columns under Biaxial Loading

A numerical method to investigate the ultimate strength behavior of thin‐walled steel box columns subjected to axial load and biaxial end moments is presented in this paper. The columns are of uniform cross section along the length and simply supported at the ends. The local buckling of the component plates is taken into account by applying the effective width formulas proposed in an earlier paper. Moment‐curvature‐thrust relationships for a locally buckled box section are developed by using the tangent stiffness method, and the column analysis is then carried out by integrating, numerically, the moment‐curvature‐thrust relationships along the length. Due allowance is made in the analysis to account for imperfections such as initial column deflections and welding residual stresses. The accuracy of the method is established by comparison with limited experimental results for uniaxially loaded columns. Results for biaxially loaded columns are presented in the form of interaction diagrams. Several parameters such as plate slenderness, column slenderness, level of residual stress, axial load, and load path have been considered.