Seismic enhancement of RC exterior beam-column joints using Ultra High Performance Concrete layers

This paper presents an in-depth study of the structural behavior of exterior beam-column joints retrofitted with Ultra High Performance Concrete (UHPC) under reversed cyclic loading. The focus is on evaluating the effectiveness of UHPC in enhancing the seismic performance of reinforced conventional concrete joints, particularly in terms of energy dissipation, stiffness degradation, and crack propagation. The study includes numerical analyses using ABAQUS software to simulate the response of conventional concrete (CC) joints and UHPC-retrofitted joints under cyclic loading. The results demonstrate that the UHPC retrofitting significantly improves the seismic resilience of exterior joints, with notable increases in load-carrying capacity, ductility, and energy dissipation. The maximum load of UHPC-retrofitted joints was found to be 18.8% higher than that of the conventional concrete joints, and they exhibited a more controlled displacement response. Additionally, the secant stiffness of UHPC-retrofitted joints was superior throughout the loading cycles, particularly at higher drift levels. Energy dissipation also showed a consistent advantage for the UHPC-retrofitted joints, with up to 22% higher energy absorption at the maximum loading compared to the conventional joints. Furthermore, damage evolution analysis indicated that while both joint types exhibited X-shaped crack patterns, the UHPC-retrofitted joints displayed delayed and less severe crack propagation.