Mainshock-Aftershock Ground Motion Sequences Selection and its Implication on Bridge Seismic Fragility

In seismic-prone regions, the evaluation of structural performance of bridges under mainshock-aftershock ground motion sequences is imperative for ensuring their safety and facilitating effective response measures. However, the limited availability of real-recorded mainshock-aftershock ground motion sequences for region-specific condition results in the adoption of artificially generated sequences for seismic fragility assessment of bridges. This study presents a new approach for the artificial generation of ground motion sequences by quantifying the relationship between parameters of real-recorded mainshock-aftershock sequences, while also considering regional seismicity. The proposed framework is employed to obtain a suite of region-specific mainshock-aftershock sequences for the Himalayan region, and is subsequently applied to a case-study bridge for vulnerability assessment. An experimentally validated bridge numerical model is developed to simulate the degradation caused by multiple cyclic loadings of mainshock-aftershock sequences. An optimal engineering demand parameter is identified to capture the cumulative damage under mainshock-aftershock sequences and seismic fragility curves are developed using incremental dynamic analysis-based approach. Results reveal a higher seismic fragility under ground motion sequences compared to mainshocks alone, with similar trends observed across different bridge geometries. Notably, the finding indicates a close match between the seismic fragility curves developed using mainshock-aftershock sequences selected through the proposed framework and those derived using real-recorded sequences.