Rintc project: Nonlinear analyses of Italian code-conforming base-isolated buildings for risk of collapse assessment

Abstract

This paper reports on the results of an ongoing Research Project aimed at computing the risk of collapse of new buildings conforming to the Italian Seismic Design Code. Companion papers describe the overall Research Project, funded by the Italian Civil Protection Department (DPC), its different areas of application (reinforced concrete, masonry, steel buildings, etc), the overall seismic risk calculation procedure and the ground motion selection process followed to identify the recorded ground motions used for the multi-stripe analyses for twenty different ground motion intensities. This paper describes the nonlinear analyses on a number of reinforced concrete (RC) buildings equipped with different isolation systems. Base isolation is one of the most widespread techniques currently used for seismic protection of buildings and their equipment. The present study presents the results for a six storey RC building isolated with different base seismic isolation systems based on: (i) 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 considering different suitable combinations of stiffness and damping or friction. The failure conditions of the proposed isolation systems and peak responses of building have been evaluated through nonlinear dynamic analysis performed under bidirectional ground motions, considering twenty couple of natural earthquakes for ten different peak ground accelerations. The results point out that all isolation systems work effectively in limiting the building damage for seismic intensities much higher than the design earthquake. On the other hand, they have a little margin to collapse beyond the design seismic intensity.