An efficient warping model for elastoplastic torsional analysis of composite beams

In this paper, we present an efficient warping model for nonlinear elastoplastic torsional analysis of composite beams developed based on Benscoter warping theory. A major challenge here is how to account for the evolution of warping functions efficiently as materials yield at various locations at different rates. Here, we propose to describe the warping displacement using a linear combination of two asymptotic warping functions with corresponding warping degrees of freedom. The asymptotic warping functions are calculated only once initially by solving the extended St. Venant equations under two material conditions: purely elastic condition and fully plastic condition when no material point in the cross-section remains elastic. Only the warping degrees of freedom are updated incrementally and iteratively in analysis without evaluating the warping functions again. The proposed warping model demonstrates an excellent performance in several numerical examples despite its simplicity.