An Explainable Numerical Procedure for the Seismic Fragility and Integrity Evaluation of Existing Reinforced Concrete Buildings

The present numerical scheme deals with the investigation related to seismic fragility and integrity of RC columns of residential buildings situated in high seismic vulnerable locations. An explainable and interpretable numerical procedure is presented to quantify the influence of column stiffness and demand–capacity ratio on seismic fragility and integrity of buildings to prognose damage scenarios in future earthquakes. Nonlinear dynamic analysis is conducted using 22 far-field ground motions following FEMA P695 standards. The analysis is performed in the longitudinal and transverse direction of a building, and story drift is evaluated for three damage levels (minor, moderate, and excessive) corresponding to performance objectives: immediate occupancy (IO), life safety (LS), and collapse prevention (CP), respectively. Incremental dynamic analysis (IDA) curves are subsequently generated using interstory drift ratio (IDR) as a demand parameter and site-specific peak ground acceleration as an intensity measure (IM). Fragility curves are further developed to relate IM to the probability of exceeding each damage level. Critical columns are identified based on exceeding a demand-to-capacity ratio (DCR) of 1, and their stiffness results are examined to understand potential damage scenarios. Finally, fragility curves for spectral accelerations (Sa) corresponding to IM are analyzed for design basis earthquake (DBE) and maximum considered earthquake (MCE) scenarios. This integrated approach provides a valuable understanding of the seismic fragility and integrity (in terms of both member and system failure probability) of a building under varying earthquake intensities. By analyzing critical columns and their stiffness results, potential damage scenarios may be recognized for future earthquakes. This study provides insights into the seismic behavior of RC framed building columns in high seismic zones. The methodology provides an explainable numerical procedure for evaluating the seismic fragility and integrity of a building and identifying potential damage types and locations for improved seismic design and retrofitting strategies to optimize the structural integrity.