Rolling-Ball Rubber-Layer isolation system: state of the art, performance and design procedure

A rolling-ball rubber-layer (RBRL) isolation system was developed at TARRC to enable isolation of lightweight structures. The system is very versatile, a great range of equivalent natural frequencies and coefficients of damping being achievable through the independent choice of rubber spring and rubber-layer rolling track. It is suitable for isolating light structures, and much more effective at low excitations than an equivalent sliding system would be. In this paper the state of the art and the dynamic behaviour of RBRL isolation system will be restated. Subsequently, a simple and efficient procedure will be described for the design of the system: this is aimed to get the principal value of the system parameters to meet the chosen values of isolation period and damping ratio. In particular, it will be emphasized that a certain value of rolling resistance of the device could result from different combinations of the device parameters, thus leaving the final specification to be made on the basis also of preferences regarding small-deflection behaviour and cost. Finally, a future application of the isolation system for the seismic protection of a statue is presented and discussed.