Recent Advancements in Rolling Isolation Systems Using Elastomeric Spheres: Numerical and Experimental Results

Rolling isolation systems using elastomeric spheres may provide significant advantages over traditional methods (i.e., rubber bearings or frictional pendulum systems) in terms of cost-efficiency. The concept involves placing elastomeric spheres between the foundation and the superstructure. The spheres can roll and rotate in response to seismic activity, either on a concave surface or a flat one with additional restitutive elements. Energy dissipation is provided through the rolling resistance, which is due to the continuous deformation of the elastomeric material. This paper analyzes the system behavior regarding its force-displacement relationship and the deformation of the sphere material through finite element modeling and experimental tests. The results show that the creep of the ball due to the weight of the structure negatively affects the system behavior because the sphere becomes oblong. Finite element models show that it is the material closer to the inner part of the ball that mostly contributes to the final oblong shape, while the material closer to the surface contributes to energy dissipation. This shows that the oblong shape can be reduced by placing an inner steel core in the sphere (since the inner part of the ball is no longer deformed) without compromising the energy dissipation. Recent experimental tests on grout-filled tennis balls validated this behavior. Overall, the rolling isolation system using elastomeric spheres with an inner steel core could represent a robust and reliable alternative to protect structures.