RINTC-E project: The seismic risk of existing Italian RC buildings retrofitted with seismic isolation

This paper reports on the results of an ongoing Research Project, funded by the Italian Civil Protection Department, aimed at the evaluation of the risk of collapse and usability-preventing performance levels for existing buildings. This paper, in particular, describes the results of nonlinear time-history analyses (NTHA) carried out on two different RC buildings retrofitted with isolation systems. The two buildings are located in two different sites, Naples and L’Aquila characterized by medium and high seismicity for Italy, and are designed for gravity loads only and according to outdated seismic codes respectively. The buildings have been retrofitted using three different isolation systems: (i) high damping rubber bearings; (ii) rubber bearings and flat sliding bearings; (iii) curved surface sliders. The results point out that all isolation systems work effectively in limiting the onset of damage of non-structural members for seismic intensities much higher than the action required by the current design code. On the other hand, they show a little margin towards collapse, beyond the design intensity level. In particular, the collapse of the superstructure turns out to be the dominant collapse mode, especially for the building designed for gravity loads only