Impact of aftershocks on a post-mainshock damaged containment structure considering duration

During earthquake events, a mainshock may trigger a number of following aftershocks in a short time, which can cause additional damage to structures. This paper investigates the influence of aftershocks with different durations on the additional accumulative damage of containment structures considering the post-mainshock damage states. For this purpose, 15 as-recorded mainshock-aftershock records with a broad range of aftershock durations, which are scaled and adjusted to match the target spectrum using wavelet transformation, are considered in this study. The three-dimensional structural model which can capture the strength and stiffness degradation during seismic sequences is established. A normalized 'damage ratio' measuring tensile and compressive damage is proposed to quantify the accumulative damage from seismic sequences. The results indicate that aftershocks with longer durations can cause more severe accumulative damage and have a significant effect on the damage pattern. Therefore, to evaluate the safety margin of containment structures accurately, the aftershock and its characteristics of duration should be taken into account when selecting ground motion records for seismic safety assessment of a Nuclear Power Plant.