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 the risk of collapse and usability-preventing performance levels for existing reinforced concrete (RC) buildings. This paper, in particular, describes the results of nonlinear time-history analyses (NTHA) carried out on two different RC buildings, designed for gravity loads only and according to outdated seismic codes, respectively. The two buildings are located in two different sites (Naples and L’Aquila, respectively) characterized by medium and high seismicity for Italy. The buildings have been retrofitted using three different isolation systems: (i) high damping rubber bearings; (ii) rubber bearings and flat sliding bearings; (iii) friction pendulum systems. The isolation systems have been designed according to current Italian seismic code. NTHA have been per-formed under bidirectional ground motions considering twenty couple of natural earthquakes for ten different earthquake intensity levels with return period ranging from 30 to some 100000 years. The results point out that all isolation systems work effectively in limiting the onset of damage in non-structural members for seismic intensities much higher than the de-sign earthquake. On the other hand, they show a little margin towards collapse, beyond the design intensiy level. The collapse of the superstructure turns out to be the dominant collapse mode, especially for the building designed for gravity loads only.