Seismic performance and fragility assessment of BRBFs subjected to sequential earthquakes

This paper evaluates the influence of sequential earthquakes on the fragility analysis of buckling-restrained braced frames (BRBFs). Sixty-three ground motions recorded during sequential earthquake events were selected and scaled based on intensity vectors to construct a comprehensive dataset for sequential ground motion analysis. This dataset was used as input for incremental dynamic analysis (IDA) of 4-, 8-, and 12-story prototypes. Low-cycle fatigue fracture of BRBs was considered in the numerical models for the prototypes. Seismic demand and capacity models were established based on the IDA results, and fragility surfaces for the prototypes were derived under sequential earthquake excitations. From these fragility functions, vulnerability index (VI) surfaces were developed, providing a direct quantification of structural damage. The study reveals that sequential earthquakes can significantly increase the cumulative plastic deformation (CPD) demands of BRBFs. The probability of BRB fracture increases with increasing aftershock intensity, particularly in higher-rise buildings due to a more discrete distribution of structural response. Additionally, when the aftershock intensity equals or exceeds the mainshock intensity, a significant increase in VI values is observed, particularly for lower BRBF structures. These findings highlight the importance of considering sequential earthquake effects in the seismic performance assessment and design of BRBFs.