Seismic performance and resilience of RC columns repaired with different jacketing strategies under variable axial loads

During earthquakes, reinforced concrete (RC) columns in underground structures are subjected to highly variable axial loads, making them susceptible to damage. Rapid post-earthquake repair is therefore critical to restoring structural safety and functionality. However, few studies have systematically evaluated repair strategies for these damaged columns under such loading conditions. This study presents a comparative numerical analysis of engineered cementitious composite (ECC), steel, and fiber-reinforced polymer (FRP) jacketing as repair strategies for damaged RC columns. Finite element models of repaired columns were developed, and nonlinear cyclic analyses under variable axial loads were conducted to assess hysteretic behavior, load-carrying capacity, ductility, and energy dissipation. To evaluate repair effectiveness, a repair performance index (RPI) integrating strength, ductility, and energy dissipation was proposed to quantify the overall seismic performance, alongside a seismic resilience assessment method incorporating average functionality, economic loss, and recovery time. The results show that ECC jacketing provides the best overall recovery performance, whereas steel jacketing achieves the highest ductility and seismic resilience. Increasing initial damage generally deteriorates the seismic performance of repaired columns, while the F3–0.35 loading protocol causes the most pronounced degradation in strength, ductility, and energy dissipation. These findings provide quantitative insights into repair strategy selection and contribute to resilience-based post-earthquake rehabilitation of underground structures.