EXPERIMENTAL SEISMIC BEHAVIOUR OF BASE ISOLATION SYSTEMS IN ITALY DURING THE 2016-2017 SEISMIC SEQUENCE IN CENTRAL ITALY

The experimental behaviour of base isolated buildings in Italy recorded during the 2016-2017 seismic sequence in Central Italy is analyzed and discussed. In all cases the epicenter distance was quite large, therefore the effects at the sites were characterized by a low energy. Both buildings seismically isolated with high damping rubber bearings (HDRB) and curved surface sliders (CSS) were considered. In the buildings with HDRBs the system is usually put in action also with low accelerations at the site and the system filters the seismic actions. As a result the acceleration in the superstructure is not amplified and the superstructure is protected, even though the resonance frequency is higher than the design one. In the building with CSSs, the accelerations were amplified to the top and the superstructure suffered significant seismic actions. This behavior can be related to a high static friction of CSSs. In all cases, the importance of an accurate non-linear analysis of their behavior under earthquakes of different magnitudes is pointed out, in order to guarantee that the seismic effects in the superstructure do not exceed those assumed in the design.