Seismic retrofit of intact and damaged RC columns using prefabricated steel cage-reinforced UHPC jackets and NSM GFRP bars

The use of high-performance materials, such as ultra-high-performance concrete (UHPC) and fiber-reinforced polymer (FRP), in the seismic retrofitting and strengthening of reinforced concrete (RC) columns has attracted wide attention. In this study, a novel prefabricated steel cage-reinforced UHPC jacket (PSRUJ) was proposed to improve the retrofitting efficiency of conventional cast-in-place UHPC jackets and combine the advantages of UHPC and steel jackets. PSRUJ was further combined with the near surface-mounted (NSM) technique to develop a new method for retrofitting the seismic performance of RC columns in buildings. To investigate the effectiveness of the proposed retrofitting method, cyclic loading tests were performed on one intact RC column retrofitted with PSRUJ and two damaged RC columns retrofitted with PSRUJ and the combination of PSRUJ and NSM glass FRP (GFRP) bars. After PSRUJ retrofitting, the load-carrying capacity, deformation capacity, and stiffness of the intact and damaged RC columns increased by (30∼46)%, (54∼74)%, and (24∼40)%, respectively. The inclusion of NSM GFRP bars further increased the load-carrying capacity but reduced the residual drift ratio while having little effect on the ultimate drift ratio of the retrofitted columns. Further, a damage index was proposed to assess the damage degree of core normal concrete and develop the peak strength and strain models for PSRUJ-confined damaged concrete. Finally, a flexural strength model was proposed for damaged RC columns retrofitted with PSRUJ and NSM bars.