Gapped Inclined Bracing (GIB) retrofit for soft-story vulnerable reinforced concrete residential buildings in Nepal

The soft-story problem is a critical issue in seismic regions like Nepal, where ground floors are left open for parking and businesses, while upper floors have infill walls, leading to stiffness differences. This study introduces Gapped Inclined Bracing (GIB) as a retrofitting strategy for soft-story buildings in Nepal. The GIB system consists of a brace with a gap element that can be designed to activate at a specific drift level, where it is desirable to prevent collapse and reduce damage while enhancing ductility. A simplified modeling approach for GIB as a compression-only element is proposed and the results are validated against the experimentation. A case study is selected to evaluate GIB's application to a real soft-story building. To date, the evaluation of GIB has been limited to the frame level. In this study, building-level performance is assessed through nonlinear pushover analysis and compared with incremental dynamic analysis. Fragility functions are developed for the building both before and after retrofitting using the capacity spectrum method (CSM) and incremental dynamic analysis (IDA). The fragility analysis results from CSM show a significant reduction in the probability of exceeding extensive damage limit state in the retrofitted building, from 30 % to 5 %, and a decrease from 15 % to 3 % for complete damage at a peak ground acceleration (PGA) of 0.35 g. Similarly, IDA results indicate reductions in these probabilities from 35 % to 8 % for extensive damage and from 16 % to 2 % for complete damage. At higher PGA levels, the probabilities remain substantially lower, indicating a reduced risk of building collapse.