Observed Seismic Behaviour of Base Isolation Systems in Italy

The observed behaviour of seismically isolated structures in different countries allowed testifying the suitability of this technique to protect structures against strong earthquakes. In Italy, up to now, base isolated buildings have been subjected only to low energy earthquakes. This paper describes and compares the observed behaviours under a low energy earthquake of three buildings with different isolation systems. In the first one, seismically isolated by means of HDRBs, the structure showed resonance frequencies higher than the design ones but the decoupling was always guaranteed also thanks to the high stiffness of the superstructure. In the second one, seismically isolated with CSSs, the onset of motion was governed by the friction, which was much higher than the design one. Finally, in a building seismically isolated with HDRBs and SDs, the onset of motion was governed by the SDs and the successive motion by the HDRBs.