Ultimate strengths of steel rectangular box beams subjected to combined action of bending and torsion

Box beams are widely used for both curved and straight structural members due to their superb torsional properties. When horizontally curved members are subjected to vertical loads only, a coupling action of vertical bending and torsion is induced. Hence, the ultimate strengths of such members must be determined interactively. In this paper, the ultimate strength interaction of rectangular steel box beams is examined by a numerical approach using a commercial FEA program, ABAQUS. Nonlinear incremental analyses up to collapse were conducted incorporating the effects of residual stresses and initial imperfections, and analysis results were compared with other researchers’ analytical and experimental test results. Simple forms of predictor equations for ultimate strengths were proposed by a means of regression analysis on the data from more than one hundred different hypothetical cases examined. Major parameters for built-up rectangular box members were aspect ratios, width-to-thickness ratios, and yield stresses of steel plate. In addition, ultimate strength interaction equations for bending-torsion and bending-shear–torsion were suggested. The suggested equations have simple forms yet well represent the lower bounds of reduced ultimate strengths due to the combined actions of bending, shear and torsion.