Isolation of light structures with Rolling-Ball Rubber-Layer system - characteristics and performance

The characteristics of the Rolling-Ball Rubber-Layer (RBRL) seismic isolation system are presented through results for force versus displacement, covering a range of amplitudes and varying sinusoidally with time, and through results for the acceleration and drift of the upper slab of an isolated model SDOF superstructure subjected to seismic excitations. It is shown how these characteristics may be described approximately by equivalent linear viscoelastic parameters K/ and K//, or alternatively K* and δ, these being functions of frequency and amplitude. This may be thought of as a frequency-domain approach. Alternatively, they may be described approximately using a non-linear time domain model, and two alternative ones are assessed here. The first has been presented previously, and a new one is presented for the first time. An objective way of comparing the accuracy of such time domain models is to compare the equivalent linear viscoelastic parameters extracted from their predictions for sinusoidal excitations, and this reveals that the new model agrees considerably better with the directly measured behaviour of the actual system. 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 rolling track layer. It is suitable for isolating light structures, and much more effective at low excitations than an equivalent sliding system would be.