Large-scale experimental investigation of sustainable, low-cost seismic isolators based on rolling rubber spheres

This study presents the results of a large-scale experimental investigation of sustainable and low-cost seismic isolators based on deformable rubber spheres rolling on concrete surfaces. A potential application of the isolators could be in low-rise masonry structures in the developing world. Parameters of investigation were the type of rolling spheres, the geometry of the concrete surfaces, and the weight that each isolator supports.

Initially, the compressive response of the isolators was examined. Subsequently, lateral cyclic tests were performed. Finally, 1170 shake-table tests were performed in 1:2 scale, with various different isolators subjected to a large number of ground motion excitations.

Results showed that the compressive strength of the spheres was substantially higher than the design load. The non-negligible deformability of the spheres leads to a lateral cyclic response that is different from the one of a rigid body model. The rolling friction coefficient ranged between 3.7% and 7.1%. During the shake table tests, the isolators reduced the acceleration transmitted to the superstructure (to 0.15 g) while maintaining reasonable peak and zero residual displacements. The shake table tests were repeatable, and the isolators did not deteriorate even after subjected to 65 ground motion excitations.