Mechanical behaviour of rubber bearings with low shape factor

This study investigates the mechanical behaviour of elastomeric bearings with a low shape factor (LSF). Such bearings can offer an effective solution for three-dimensional seismic isolation of structures, that is, isolation in vertical as well as horizontal directions. They could also be employed for developing low-cost isolation systems for developing countries due to their reduced weight and manufacturing cost. The first part of the study describes tests carried out at Tun Abdul Razak Research Centre (TARRC) on low-damping rubber double-shear test pieces and LSF bearings. The material tests are used to inform the development of a finite element (FE) model of the bearings, which is validated against the bearing test results. It is shown that the proposed FE model can be used to describe accurately the global non-linear horizontal force-displacement behaviour of the compressed bearings, while providing an insight into the local distribution of stresses and strains. It can also be used to investigate the bearing response under boundary conditions that differ from the one considered in the tests. The second part of the study illustrates the numerical simulations of shaking table tests carried out at the University of Naples Federico II on a structural prototype mounted on the low-damping LSF bearings. Useful insights are provided into the effect of the vertical bearing flexibility on the response and the attainment of critical conditions of zero tangent horizontal stiffness under horizontal displacements.