Abstract

Some commercial base isolators have been introduced in the last four decades to protect buildings from vibration and earthquakes. Typically, they are constituted by several alternating layers of rubber pads and steel (elastomeric isolator) interposed by two continuous pads, limiting vertical deformability. At the same time, they exhibit good deformation capacity in the horizontal direction when subjected to a seismic load. A very effective seismic isolator shall satisfy the following functions: good performance under all service loads, vertical and horizontal; provide enough horizontal flexibility to reach the target natural period for the isolated structure; recentering capability after the ground motion so that no residual horizontal displacement can downgrade the serviceability of the structure; provide an adequate level of energy dissipation (damping) to control the displacement that could damage other structural members. Steel-reinforced elastomeric isolators (SREIs) are the most used method of seismic isolation. Since these devices are generally too expensive due to the need to introduce thick steel plates for their supports and the high energy consumed for the manufacturing process, they are not suitable for ordinary residential buildings, especially in developing countries. Compared with SREIs, fiber-reinforced elastomeric isolators (FREIs) have considerably lower weight and can be installed between the structure in elevation and the foundation without any bonding or fastening in the so called unbonded application (UFREI), reducing costs hugely. Furthermore, without steel supports, the shear load is transferred through the friction generated between the isolator and the structure surfaces, improving the dissipation energy of the devices. The main feature of such a UFREIs is the large deformability thanks to the rollover deformation and the favorably lower lateral stiffness compared to the bonded isolator. In this paper, a series of experimental tests of the rubber compound and numerical analyses of UFREIs made of high damping rubbers (HDR) combined with glass fiber reinforcement have been performed. A HDR made of Natural Rubber and Ethylene Propylene Diene Monomer (NREPDM) blend has been considered. Finite Element shear test results have shown good dynamic performances of the proposed device.