Abstract:
In general practice of performance-based seismic assessment and dynamic analysis of building structures, the recorded ground motions from past earthquake events are selected and modified according to the site conditions and hazard level of the project’s site. For this purpose, only the effect of major earthquakes is considered for the analysis, while foreshocks and aftershocks are neglected. However, in real scenario especially for non-seismically-designed or poorly detailed RC buildings, the moderate to low magnitude foreshocks and aftershocks may also result in slight damage or stiffness degradation. Moreover, from few previous researches it was observed that repetition of earthquake events may lead to damage accumulation in the structures which can lead to significant seismic losses even if the structure is at life safety (LS) performance level. In this study, seismic performance of mid-rise RC frame structures in Pakistan has been examined under repeated earthquakes (i.e. including both fore- shocks and aftershocks). For this purpose, after a survey of typical existing RC buildings in Pakistan, one representative case study building has been selected for the detailed analysis. Its linear elastic model (on Etabs) and detailed nonlinear model (on Perform-3D) has been subjected to single-earthquake scenario as well as to several cases of repeated earthquakes. The as recorded real ground motion data was picked from the NILORE station. Incremental Dynamic Analysis (IDA) technique was used to scale the as recorded ground motions. Main- shocks, fore- shocks and aftershocks were scaled to reach the collapse limit of the frame. The seismic performance in terms of key engineering demand parameters such as story displacements, IDR (inter-story drift ratio), residual displacements and In-elastic dissipated energies of these case study buildings have been evaluated for single-earthquake and multiple-earthquake scenarios. The results show that the multiple earthquakes has no impact on the roof drift and other damage parameters but it increased the dissipated inelastic energies thus may leads to the structural damage in case of high level earthquake.
Keywords: Repeated Earthquakes, Aftershocks, Foreshocks, Pakistan, Mid-rise RC Buildings, Nonlinear time history analysis, Incremental dynamic analysis (IDA)
