Experimental characterization, design and modelling of the RBRL seismic-isolation system for lightweight structures

The Rolling-Ball Rubber-Layer (RBRL) system was developed to enable seismic isolation of lightweight structures, such as special equipment or works of art, and is very versatile, a great range of equivalent natural frequencies and coefficients of damping being achievable through choice of the system parameters. The necessity to have a simple and effective design procedure has led to a new parametric experimentation at Tun Abdul Razak Research Centre (TARRC) on the rolling behaviour of the RBRL system and load–deflection behaviour of the recentering springs. The experimental results, together with theories for the rolling resistance of a loaded steel ball on a thin rubber layer and the lateral load–deflection behaviour of cylindrical rubber springs, are used to develop a general design method for the RBRL system, which allows the system to be tailored to the specific application. Sinusoidal test results are presented for the small-deflection behaviour of the system, influenced by the presence of a viscoelastic depression on the rubber tracks beneath each ball, and an amplitude-dependent time-domain model is proposed, based on these results and on the steady-state behaviour of the system. The model is validated through comparison with previously performed shaking-table tests. Attention is here restricted to uniaxial behaviour.