Impact of inadequate column performance and repair techniques on the seismic performance of RC buildings

Nepal lies in a seismically active zone, and recent earthquakes, such as the Gorkha (2015) and Jajarkot (2023) earthquakes, have caused the failure of many reinforced concrete (RC) frame structures. Many of these failures occur in non-engineered buildings and those constructed based on outdated Nepalese standards. This research aims to observe the seismic performance of existing structures, particularly non-engineered buildings located in the hilly regions of Far Western Nepal. Three representative non-engineered structures were selected for analysis, and the performance of structural columns was evaluated using the response spectrum method and nonlinear static analyses. Three retrofitting techniques were considered: concrete jacketing, steel jacketing, and the addition of steel bracings. The results were analyzed and compared in terms of capacity curves, inter-story drift, displacement, stiffness, and column design parameters. Results show that retrofitting significantly improves lateral load resistance, with steel bracing reducing inter-story drift by up to 80% and enhancing base shear capacity by over 2000 kN. P-M-M interaction ratios dropped from 1.557 in unretrofitted columns to as low as 0.148 in retrofitted ones, indicating improved structural stability. By adopting retrofitting techniques in poorly designed columns, the overall seismic performance of the structures improved, with an adequate level of ductility. Among the methods, adding steel bracing provided a suitable improvement in seismic performance, though jacketing in columns also proved to be a good option for retrofitting. In conclusion, the study indicates that retrofitting techniques can substantially improve the seismic capacity of poor-strength buildings, providing safety and resilience to such structures.