Proposal and Validation of an Equivalent Damping Equation for Predicting the Response of Damaged RC Buildings in Aftershocks Using E-Defense Data of a Three-Story Building

One method to evaluate building safety following a mainshock is to evaluate its ability to survive subsequent aftershocks. Previous studies investigating the influence of mainshock-aftershock (MA) sequences often assume that the intensities of the mainshock and aftershock are equal, even though recent events have shown that the intensity of the aftershock may be greater. Furthermore, past studies often do not explicitly account for damage which may already exist due to previous seismic events. This study addresses these gaps by developing a method to estimate the maximum response of a damaged reinforced concrete (RC) building subjected to an aftershock based on the Capacity Spectrum Method (CSM). This was done by revising the equivalent damping equation provided in the Japanese Building Standard Law, which is used to determine the demand reduction factor for CSM applications, by modifying hysteretic parameters to account for existing structural damage. Experimental data from a large-scale shake-table test of a three-story RC building performed at the E-defense facility in Japan was used to validate this approach. It was found using the E-defense data that: (i) assumptions adopted for modifying the hysteresis curve were reasonable, and (ii) the use of the proposed equivalent damping equation in CSM resulted in much lower error (0.6%) compared to an existing equation from literature which had an error of 42%. Based on these findings, the proposed approach could be used to quantify the remaining deformation capacity of buildings against future seismic events.