Experimental study of grout-filled, reused tennis balls as seismic isolation bearings for lightweight structures

This paper describes the lateral cyclic response of a low-cost seismic isolator. The system comprises a grout-filled, reused tennis ball rolling on concrete plates. The isolator could be used in lightweight residential structures. Initially, the compressive response of the system was characterized. Subsequently, full-scale isolators were tested in combined compression and lateral cyclic loading. The following parameters were investigated: the testing velocity (frequency), the bearing load, the degradation due to consecutive loading, and the specimen-to-specimen variability. Results showed that the lateral cyclic response of the isolators is bilinear and can be approximated by rigid-body equations, whereas the values of the rolling friction coefficient and the yield displacement are suitable for seismic isolation applications. The specimen-to-specimen variability was minimal. Unlike sliding isolation systems, an increased bearing compressive load leads to a higher rolling friction coefficient. Analytical equations are offered to describe this effect. The rolling friction coefficient does not depend on velocity (frequency), and the isolators did not deteriorate under consecutive loading.