Effects of ground motion spectral characteristics on RC frame fragility considering liquefaction

Seismic liquefaction represents a persistent and complex engineering challenge in soil dynamics. Post-earthquake damage investigations have shown that damage to buildings caused by site liquefaction constitutes a significant proportion of all seismic damage. The spectral characteristics of ground motions exert a predominant effect on structural damage, and an important issue that needs to be addressed is accurately describing how these spectral characteristics influence the structural fragility. A simplified six-story reinforced concrete (RC) frame model was established. The ratio of peak ground displacement to peak ground acceleration (referred to as Rd2a) was adopted as an indicator of spectral characteristics of ground motions. The collected ground motions were classified into five groups based on their respective Rd2a values. Using the in-built Incremental Dynamic Analysis (IDA) kit on the OpenSees platform, fragility curves of the simplified RC building were calculated under different Rd2a values to further assess the effect of the ratio of the peak ground displacement to peak ground acceleration on structural fragility. Additionally, 22 real ground motion records from liquefied sites (hereafter referred to as liquefied ground motions) and a same number of records from non-liquefied sites were also analyzed. The results underscore the distinct vulnerability patterns of structures on liquefied ground, revealing that the unique spectral shifts inherent in liquefied motions significantly intensify structural fragility compared to non-liquefied conditions.