Non-ductile reinforced concrete (RC) members are common in the existing RC frame buildings with the old seismic code (lightly and inadequately detailed transverse reinforcement) and may suffer shear failure or flexure-shear failure. To investigate the failure behaviors of those RC structures, performance-based numerical models are needed. Thus, a new fiber frame element on Winkler-based foundation including the interaction effects between shear and flexure was developed to analyze non-ductile RC frames resting on foundation, in this study. The proposed element is formulated for implementation in displacement-based finite element formulation under the kinematic assumptions of Timoshenko beam theory. As a result, axial and flexural mechanisms are automatically coupled through the fiber-section model, while shear and flexural actions interact via the UCSD shear-strength model within the framework of modified Mergos-Kappos interaction procedure to evaluate sectional shear force and shear stiffness within the shear constitutive law. Therefore, the presented model is simple, but able to capture several salient behaviors of non-ductile RC frames resting on foundation, including interaction between shear and flexure, soil-structure interaction, degradation of shear strength due to inelastic flexural deformation, and shear failure. Those features and efficiency of the proposed model are demonstrated by two numerical simulations in this work.
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