Experimental investigation of twin confinement effects of FRP and steel rebar on cyclic compressive behavior of concrete

Abstract Concrete confinement is one of the most effective methods to increase the ductility of structural reinforced concrete elements. Externally bonded fiber reinforced polymer (FRP) is a technique for seismic retrofit and rehabilitation of existing structures. Consequently, evaluation of the cyclic behavior of concrete members that are confined simultaneously by transverse steel reinforcement and FRP is of great significance. During recent decades, a significant number of valuable experimental studies have been conducted and various comprehensive analytical models have been proposed to take into account the effect of confinement provided by steel rebar or FRP. However, less attention has been paid to the twin confining effect of FRP and steel reinforcement on the cyclic behavior of concrete. In this study, a total of 32 concrete specimens were tested under monotonic and cyclic axial compression. The specimens were confined using steel bars or/and CFRP with different reinforcement and retrofitting schemes. Afterward, using the obtained experimental results, the accuracy of a previously developed elasto-plastic and fracture-based model is evaluated. Furthermore, minor modifications are proposed to take into account the effect of concrete cover, longitudinal reinforcement, continuous spiral confinement, and weak confining effects. The modified model is used to predict the behavior of the tested specimens with respect to the experimental loading paths. The results are in good agreement with the experimental data, indicating that the model can accurately simulate the cyclic behavior of concrete confined with FRP and steel rebar, simultaneously.