Inelastic Bending and Torsion of Steel I‐Beams

Abstract

The inelastic combined bending and torsion of I‐section beams is investigated in this paper using the finite‐element method. The elastic‐plastic load‐deformation relationships of beams under combined bending and torsion are determined by taking into account the effects of large deformations, material inelasticity, and initial conditions of residual stresses and geometric imperfections. The interactions between in‐plane bending, flexural‐torsional buckling, and torsion are studied. The effects of secondary bending actions about the minor axis caused by torsional rotations are important for the interaction between bending (with flexural‐torsional buckling) and destabilizing torsion. Interaction equations for the design of I‐section beams against combined bending and free torsion, and against combined flexural‐torsional buckling and destabilizing torsion, are proposed. It is found that a commonly quoted circular interaction equation for combined bending and torsion does not always provide a true lower bound for I‐section beams.