Effect of different aspects of multiple earthquakes on the nonlinear behavior of RC structures

Abstract Observations from field investigations have shown that a structure may be subjected to more than one earthquake in a relatively short period of time. Since after every single earthquake, a structure faces a stiffness and strength degradation, it may not be able to withstand subsequent shaking especially when seismic retrofit is not an option due to the short time intervals between the successive earthquakes. Therefore, it is necessary to consider effects of repeated shaking on the behavior of structures prone to multiple earthquakes. Although many studies have been performed so far, there are some significant deficits which need more attention. Some of the important limitations in most of the recent studies include: (1) the use of ground motion data from uncorrelated events occurring at different locations and times; (2) utilization of simple models that do not contain appropriate damage features; and (3) no proper consideration to the effects of earthquake direction, aftershock polarity, structure irregularity, and the vertical component of the earthquake. The objective of this study is to overcome the aforementioned limitations through using a robust finite element model that simulates the degrading behavior of reinforced concrete structures subjected to as-recorded seismic sequences. For this purpose, the nonlinear response of two eight-story reinforced concrete buildings (both regular and irregular in height) is evaluated. The buildings are subjected to a suite of ground motion records obtained from the recent 2010–2011 Christchurch earthquake sequence. Dynamic response history analyses are conducted to investigate the effects of: 1) damage from previous ground motions; 2) earthquake direction; 3) aftershock polarity; and 4) the vertical component of the earthquake. The results presented in this study indicate that earthquake direction (in the irregular building), structure irregularity, and the vertical earthquake component can have a considerable effect on the response of structures subjected to multiple earthquakes. Findings also show that aftershock polarity can significantly change the response of the irregular structure.

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