Enhancing the performance of heat-damaged rectangular RC columns using prestressed FRP confinement

To retrofit non-seismically detailed reinforced concrete (RC) columns over seismic loads, the application of fiber-reinforced polymer (FRP) materials has become a widely accepted technique. However, for RC columns exposed to high-temperature conditions, the structural performance of this technique, especially in the case of rectangular ones, is a serious concern. This paper aims to experimentally evaluate the effectiveness of prestressed FRP strips in actively enhancing the axial performance of heat-damaged rectangular RC columns by mitigating the expansive behavior of thermally deteriorated concrete. For this purpose, axial compressive loading tests are carried out on a series of heat-damaged rectangular RC column specimens. The specimens are first submitted to a specific heating condition with a high exposure temperature of 700 °C. Subsequently, the post-heated specimens are confined by the strengthening approach using prestressed FRP strips. The experimental results in terms of stress-strain curve, load-carrying capacity, deformability, axial stiffness, and failure mode are presented and discussed. Furthermore, the performance of the prestressed FRP confinement imposed on heat-damaged concrete is also compared with that of the conventional passive confinement for both ambient and fire exposure conditions. The results evidence that the prestressed FRP confinement system is capable of sufficiently improving the compressive behavior of heat-damaged rectangular RC columns.