Numerical simulation of RC infill walls under cyclic loading and calibration with widely used hysteretic models and experiments

Addition of reinforced concrete (RC) infill walls into the structural system has been a commonly preferred strengthening technique within the last decades for seismic rehabilitation of RC frames. As a consequence, generating a representative numerical model of an RC infill wall has become an important issue. As the initial step of this study, measured structural responses of two selected well-known large-scale RC infill wall experiments subjected to displacement controlled cyclic loading are taken into account. Later, by calibrating the numerical model prepared in Perform-3D computer program utilizing fiber cross-sections, a practical and a compatible analytical model is obtained and proposed herein. Structural systems of the experiments are mathematically modeled by elements consisting of vertical and horizontal fiber layers to represent the bending/axial behavior and to control the out of plane displacements, respectively. Nonlinear behavior of the reinforcing steel is represented by a tri-linear backbone curve without strength degradation, while a multi-linear hysteretic behavior considering the strength loss is utilized for the structural concrete. Furthermore, those recently conducted experiments are simulated by a couple of widely used hysteretic models for comparative purposes, which are preferred in most cases by the researchers during the analytical investigation of RC structures, so that their adequacy for reflecting the nonlinear behavior of infill walls are also studied. It is shown with comparisons for the experimentally measured and the analytically derived results that the calibrated mathematical model proposed herein is more compatible with the measured values than the widely used hysteretic rules for capturing the behavior of these types of frames retrofitted by RC infill walls under reversed cyclic loading. Although numerical simulations are carried out for a limited number of tests and it is assumed that sufficient amount of anchoring dowels is provided at the interface of the existing frame and the RC infill, the proposed calibrated model conforms to both experiments’ measured responses by means of seismic behavior for not only the undamaged single bay frames converted to the RC infill wall, but also pre-damaged multi-bay strengthened structures, which include structural deficiencies like low concrete strength, inadequate stiffness and insufficient confinement.