Fragility functions of SDOF systems by accelerograms with spectra variable in shape with magnitude

Numerous researchers have proposed methodologies for the evaluation of the fragility function of a building, e.g. by means of incremental dynamic analysis or multiple stripe analysis. However, in almost every case, numerical analyses are carried out by means of a single set of accelerograms that is scaled in acceleration to simulate earthquakes with different magnitude. Therefore, these numerical analyses neglect that other seismological parameters (e.g. the shape of the pseudo-acceleration response spectrum and the significant duration of the accelerogram) may vary with the magnitude of the earthquake. This simplification in the seismic assessment of buildings is generally due to the difficulty in selecting or generating accelerograms that are compatible with multiple seismological parameters. In this paper, the multiple stripe analysis is applied to SDOF systems with different inelastic responses taking into account also the variation in the shape of the pseudo-acceleration response spectrum as a function of magnitude, as suggested by the National Institute of Geophysics and Volcanology for the Italian territory. To this end, several sets of artificial accelerograms are generated by means of the program SIMKQE so that each set is compatible with a pseudo-acceleration response spectrum characterized by an assigned magnitude. The results highlight the importance of the shape of the response spectrum on the fragility function of SDOF systems and relate it to the period of vibration of the system and the degradation of the response of the system.