Axial-flexure-shear model for seismic analysis of RC thin-walled hollow piers

Reinforced concrete (RC) thin-walled hollow piers often exhibit prominent flexure-shear effect, especially when subjected to pulse-like earthquakes. To predict the axial-flexure-shear behaviors of such hollow piers, an innovative approach named Axial-Flexure-Shear-Interaction-Membrane-Beam-Truss-Element-Model (AFSI-MBTEM) is developed. In the AFSI-MBTEM, the RC hollow pier is discretized into membrane elements, beam elements, and truss elements. The bi-scalar damage-plasticity concrete model is used in the membrane elements to consider the compression-softening effect and the degradations of strength and stiffness. Concrete01 and ReinforcingSteel are adopted as uniaxial materials for beam-column elements and truss elements. The axial-flexure and axial-shear behaviors are coupled through the multi-dimensional material and the integration of multiple element types. The numerical approximation of the AFSI-MBTEM for rectangular and circular RC hollow piers is presented, and it is implemented in OpenSees. A series of RC thin-walled hollow piers with different failure modes under cyclic loading were collected for validation. The predictions against experimental results indicate that the AFSI-MBTEM captures the cyclic responses of RC hollow piers with excellent accuracy, convergence, and efficiency. However, overestimations of yield plateau and energy dissipation, along with sudden drops at large ductility, are observed in simulations using the flexure model. The dynamic responses of the full-scale hollow piers under 223 pulse-like motions further demonstrate the superiority of the AFSI-MBTEM. Meanwhile, the flexure model underestimates their dynamic responses due to the enhanced energy dissipation capacity and the neglect of shear effects.