INELASTIC BENDING AND TORSION OF STEEL I-BEAMS

The inelastic combined bending and torsion of I-section beams is inves tigated in this paper using the finite-element method. The elastic-pla stic load-deformation relationships of beams under combined bending an d torsion are determined by taking into account the effects of large d eformations, material inelasticity, and initial conditions of residual stresses and geometric imperfections. The interactions between in-pla ne bending, flexural-torsional buckling, and torsion are studied. The effects of secondary bending actions about the minor axis caused by to rsional rotations are important for the interaction between bending (w ith flexural-torsional buckling) and destabilizing torsion. Interactio n equations for the design of I-section beams against combined bending and free torsion, and against combined flexural-torsional buckling an d destabilizing torsion, are proposed. It is found that a commonly quo ted circular interaction equation for combined bending and torsion doe s not always provide a true lower bound for I-section beams.