Fragility curves of sequential earthquakes for RC buildings in Japan

Structures in earthquake-prone areas may suffer from accumulative damages caused by sequential shocks, including the mainshock and aftershock of an earthquake or several strong motions throughout their service lifespan. Sequential shocks lead to a decrease in the capacity of structures. Nevertheless, seismic fragility curves and their applications do not often consider the sequential effect. This study investigates the impact of sequential seismic events on seismic fragility curves of 3-, 6-, and 9-story reinforced concrete buildings constructed before and after 1982 in Japan. The research proposes analytical fragility curves based on dynamic nonlinear multi-degree-of-freedom analyses under the influence of single shock and sequential shock of recorded motions of six destructive earthquakes in Japan. The results demonstrate that the seismic sequence increases the probability of damage ratio. This increase in the fragility curve follows the Gaussian function. The study presents a regression model that can be used for other seismic areas to estimate the effect of seismic sequences on single shock seismic fragility curves.