Correlation between intensity measures and seismic response of deformable rolling seismic isolators

Seismic isolation is a highly effective method of seismic protection. However, its high cost has limited its application in lightweight structures. This study presents a low-cost, high- performance seismic isolator comprising a deformable elastomeric sphere rolling on concrete plates, one of which is concave to provide gravitational restoring force. Since the sphere deforms under compression, bilinear models cannot describe its response. A five-parameter analytical model is used to describe the seismic response of the isolators. The model is calibrated using lateral cyclic tests and validated against shake table tests. It captures all stages of the flag-shaped response, including positive and negative stiffness, the restoring force due to plate geometry, and the rolling friction coefficient. The model is then used to identify ground motion intensity measures (IMs) that best correlate with the isolator response in terms of maximum acceleration and maximum displacement. A wide range of design scenarios (considering different eigenperiods and rolling friction coefficients) is analyzed using 173 historical ground motions and 15 commonly used IMs. Results show that Peak Ground Acceleration (PGA) and Arias Intensity are the two best IMs, with the former correlating better with superstructure accelerations and the latter with isolator displacements.