Shake-table testing of low-cost, high-performance seismic isolators based on rolling rubber spheres

This study presents the results of a large-scale experimental investigation of low-cost, high-performance seismic isolators based on deformable rolling rubber spheres. The spheres roll on flat or concave concrete surfaces. Different types of spheres and design scenarios were examined. A potential application of the proposed isolator could be in low-rise structures in regions where conventional seismic isolators are unaffordable. The spheres were initially subjected to monotonic uniaxial compression and sustained compression under vertical load to examine their compressive behavior. Subsequently, lateral cyclic tests under large displacements were performed. Finally, a total of 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 lateral cyclic response differs substantially from the one that a rigid body model would suggest due to the non-negligible deformability of the spheres. The rolling friction coefficient ranged between 3.7% and 7.1%. Hence, it is suitable for seismic isolation applications. The spherical concrete plates increase the restoring force of the system. When tested in a shake table under 1170 ground motions, the isolators substantially reduced the acceleration transmitted to the superstructure (to less than 0.2 g) while maintaining reason-able peak and zero residual displacements. Notably, the shake table tests were repeatable, and the isolators did not deteriorate even after subjected to 65 ground motion excitations.
COMPDYN Proceedings
COMPDYN 2023