Mixed 3D beam element with damage plasticity for the analysis of RC members under warping torsion

This paper describes the simulation of RC members with a three-dimensional (3D), 2-node beam finite element (FE) that includes warping of the cross section. A previously proposed FE formulation is extended to allow the description of structural members with softening material behavior. The governing equations are derived from an extended four-field Hu-Washizu variational principle, with independent interpolation of the warping displacement field from the rigid section displacement, the generalized section deformation, and the material stress fields. A fiber discretization is used for the numerical integration of the nonlinear material response of the composite cross sections with a new plastic-damage model for the material description of the concrete fibers. The element state determination is based on a numerically efficient predictor-corrector scheme for the evolution of the internal variables of damage plasticity. The paper concludes with correlation studies of RC structural members under monotonic and cyclic loading and discusses the effect of cross-section warping on the damage evolution.