Experimental and analytical investigation on the lateral response of ball rubber bearing isolators

Recent earthquakes demonstrated that modern seismic design and retrofit of constructions should target damage containment to reduce the direct and indirect economic losses and downtime. In this context, the use of base isolation as seismic protection strategy is becoming popular. A variety of devices is available on the market. Elastomeric and metallic sliding devices are the most common type of isolators. Ball rubber bearings (BRBs) combine the practical use and the low maintenance cost of elastomeric bearings with a friction-based dissipation due to the steel balls of the inner core. Although many tests were performed to characterize the lateral response of BRBs, their stiffness, the maximum displacement capacity and the damping, further studies are needed to clearly identify the main variables and their effects on the lateral response. This research paper aims at developing a design-oriented formulation to estimate the equivalent damping, the characteristic strength and the lateral stiffness of BRBs. In order to calibrate and validate the proposed formulation, experimental tests are performed varying the axial load pressure and maximum imposed displacement. Furthermore, all the tests available in literature are collected in a unique database. Simple considerations on the influence of the different design parameters are discussed and used to calibrate reliable design formulations to be used in the design practice