Cyclic Stress–Strain Relationships of FRP Confined Concrete Members

External confinement of columns of existing reinforced concrete buildings using fiber-reinforced polymer (FRP) composites can significantly increase the ductility and compressive strength of structural members against seismic actions. Therefore, knowledge on the behavior of FRP confined concrete/reinforced concrete members under cyclic stresses is vitally important for realistic prediction of seismic performance of retrofitted structures. In this study, available experimental data on the cyclic stress–strain behavior of FRP confined concrete/reinforced concrete members are evaluated in a comparative manner, and accuracy of several stress–strain models proposed for FRP confined concrete is discussed in terms of prediction of the skeleton curves, as well as the unloading–reloading branches of the cyclic stress–strain relationships of the tested samples. Furthermore, a new model is proposed for the prediction of unloading and reloading branches based on the cyclic tests carried out specifically for this purpose. The predictions of the proposed model and two other available models proposed for cyclic loading are compared with experimental data, and a satisfactory agreement is observed between the predictions and experimental data.