ULTIMATE STRENGTH DESIGN OF BIAXIALLY LOADED STEEL BOX BEAM-COLUMNS

This paper is concerned with the analysis and design of box beam-colum ns subjected to axial load applied at biaxial eccentricities. A spread -of-plasticity method to predict the ultimate strength of box beam-col umns of compact cross-sections is proposed. The method is then extende d to study the behaviour of thin-walled beam-columns in which the effe cts of local buckling are taken into account in terms of the effective width of the component plates. The analytical results are compared wi th the corresponding results obtained from experiments carried out by the authors. Design formulae are proposed to predict the ultimate stre ngth of beam-columns of non-compact cross-sections under biaxial loadi ng. Finally, some optimisation results for designing thin-walled beam- columns with minimum weights, satisfying the strength limit state and other design constraints relevant to typical conditions in practice, a re provided.