The fixed-strut-angle finite element (FSAFE) model for reinforced concrete structural walls

Abstract

This paper evaluates the capabilities and limitations of a relatively simple mesoscopic finite element modeling approach, referred to as the Fixed Strut Angle Finite Element (FSAFE) Model, in simulating the hysteretic lateral load behavior of reinforced concrete structural walls designed to yield in flexure. The behavioral characteristics of the constitutive panel (membrane) elements incorporated in the model are based on a simple fixed-crack-angle formulation, where normal stresses in concrete are calculated along fixed crack directions using a uniaxial stress–strain relationship, with modifications to represent biaxial softening effects. The constitutive panel model formulation also incorporates behavioral models for the shear-aggregate-interlock effects in concrete and dowel action on reinforcing bars, constituting the shear stress transfer mechanisms across cracks. Model predictions are compared with experimentally-measured responses of benchmark wall specimens with a variety of configurations and response characteristics. Accurate predictions are obtained for important global response attributes of the walls prior to failure, including their lateral load capacity, stiffness, ductility, and hysteretic response characteristics; although instability failures related to buckling of reinforcement and/or out-of-plane instability of the wall boundary region are not captured. The model provides accurate estimates of the relative contribution of nonlinear flexural and shear deformations to wall lateral displacements, as well as local response characteristics including the distribution of curvatures, strains, and shear deformations on the walls, prior to failure. Based on the response comparisons presented, model capabilities are assessed and possible model improvements are identified. Overall, the FSAFE model is shown to be a practical yet reliable modeling approach for simulating nonlinear wall behavior, which can be used within the framework of performance-based seismic design and assessment of building structures.