Prestressed CFRP–UHPC strengthening of RC square columns with joint enhancement: Failure mechanisms and seismic performance

To address the debonding issue at the interface between the UHPC layer and the column base in ultra-high performance concrete (UHPC)-strengthened RC columns and improve their seismic performance, this paper proposes a node-enhanced prestressed CFRP-UHPC composite strengthening method. Eight RC square column specimens were designed to systematically investigate the effects of different strengthening methods and axial compression ratios on seismic performance, with a focus on analyzing the improvement of joint enhancement measures on the integrity and failure mechanism of the specimens. Experimental results show that, after applying this strengthening method, the ductility coefficient, energy dissipation capacity, and bearing capacity of the specimens increased by up to 50.0 %, 117.0 %, and 61.0 %, respectively. The joint enhancement measures effectively enhanced the bonding performance between the UHPC layer and the base, as well as the collaborative working ability with the core concrete, while the prestressed CFRP significantly suppressed lateral deformation and improved capacity. Furthermore, based on validating the accuracy of the numerical model, an optimization analysis of the strengthening scheme was conducted, leading to further improvement in the seismic performance of the optimized specimens. Finally, a calculation method for the compression-bending bearing capacity of CFRP-UHPC-strengthened columns was proposed, and the calculated results showed good agreement with experimental data, verifying the rationality of the method. • Methods for preventing horizontal cracks in fiber-reinforced concrete RC columns are proposed. • UHPC and CFRP are combined to strengthen RC columns, with failure mechanisms analyzed. • Simulation methods address plastic hinge relocation via structural reconstruction. • A bending-capacity calculation method for CFRP-UHPC strengthened RC columns is proposed.