Base isolated residential buildings: Field tests, laboratory experiments, numerical simulations

The Solarino project involves the retrofit of two reinforced concrete residential buildings in Eastern Sicily. The retrofit was implemented by using a hybrid base isolation system, which consists of high damping rubber bearings and low friction sliding bearings. In 2004, one of the buildings was tested under free vibration field tests. In December 2014, a high damping rubber bearing of the Solarino project was tested in the Laboratory of University of Basilicata in Potenza. The free vibration field tests and the laboratory cyclic shear tests are used for the parameter identification and calibration of proper models for the simulation of the isolation system. Primarily, the research effort was focused on defining appropriate models for the simulation of high damping rubber bearings (HDRB), which provide the largest amount of force produced by the hybrid isolation system. It is been almost 30 years since the first use of HDRB in seismic isolation for buildings, and the present work summarizes the most important models for the simulation of the shear behavior under compression of such bearings. The main issues raised by the research community for the simulation of the behavior of these devices are discussed and analyzed. Due to the uncertainties in the behavior of these devices, recent codes suggest to use simple models and of upper and lower bounds to the nominal properties of the bearings. To this end, a new simple model with clear mechanical formulation for the simulation of the shear behavior under compression of the HDRB is presented, based on laboratory cyclic tests. The 10-parameter model consists of four elements connected in parallel. Three of them are simple and well-known elements, i.e. a non-linear elastic spring (to account for stiffness hardening and/or softening), two elastoplastic elements (to account for energy dissipation), while the fourth one is a new simple hysteretic damper used to distinguish between the behavior of HDRB during the loading and unloading phases of their dynamic response.