The effects of mainshock-aftershock in successive earthquakes on the response of RC moment-resisting frames considering the influence of the vertical seismic component

Abstract

The sequential earthquakes and the vertical component of earthquakes can cause extensive damages to structures. In this study, by applying the incremental dynamic collapse analysis, considering the stability, final curvature and interstory drift, as performance criteria for the intact and damaged structures under the mainshock, the fragility curves are studied. The analyses have been performed for two reinforced concrete moment-resisting frames (RC-MRFs) of 6- and 10-story buildings by considering two scenarios of the horizontal component and the simultaneous effects of the horizontal and vertical components of the earthquakes for two structural conditions with and without damage. The provided fragility curves indicate the probability of the collapse of the structures due to the intensities of the earthquakes and the response of the structures, as well as the exceedance probability of the maximum interstory drifts of the damaged structures under the impact of aftershocks from first damage state (DS₁) and second damage state (DS₂) in terms of earthquakes intensities. In the DS₁, the structure under the mainshock reaches a maximum interstory drift of 0.5%, and in the DS₂; it reaches a maximum interstory drift of 0.8%. The results obtained using the incremental dynamic analysis (IDA) method indicate that the damages caused by the previous events and considering the vertical component of the earthquake have significant influences on the interstory drift related to the collapse of the structure. Considering the vertical and horizontal components of the earthquake, as well as the seismic sequence reduces the maximum interstory drift corresponding to the collapse of the structure. By applying the regression analysis some practical equations were submitted to be employed in similar cases as a guideline.