Impact of the type of the target response spectrum for ground motion selection and of the number of ground motions on the pushover-based seismic performance assessment of buildings

The impact of the type of target response spectrum and the number of ground motions on the response of buildings is investigated. The parametric study involves the selection of ground motions based on the Eurocode 8 spectrum, a conditional spectrum using the official seismotectonic model of Slovenia, a uniform hazard spectrum based on the seismotectonic model of the SHARE project, and the corresponding conditional spectrum. In addition to the variation of the target response spectrum, the number of selected ground motions was varied from 7 to 60. Selected sets of ground motions were used to investigate the seismic response of eight reinforced concrete buildings with fundamental vibration periods from 0.15 s to 1.76 s. The aim of the study was to analyse the variation of target displacements obtained by a pushover-based method, i.e. the median displacement corresponding to a seismic intensity with a return period of 475 or 2475 years, and the median spectral acceleration causing collapse, which was estimated by incremental dynamic analysis. It was found that the target spectrum and the number of ground motions have a limited impact on the target displacement, especially if it corresponds to seismic intensities with a return period of 475 years. Additionally, the impact of the number of ground motions on the median spectral acceleration causing collapse is much lower than the impact of the target response spectrum. When the conditional spectrum was used as the target spectrum for ground motion selection instead of the design response spectrum prescribed by Eurocode 8, the resulting median spectral acceleration causing collapse increased by a factor of between 1.2 and 2.3.