Experimental investigation on low-cost full-scale fiber reinforced elastomeric isolators tested in unbonded configuration

Seismic base isolation is nowadays a mature technology to mitigate seismic risk in earthquake-prone regions. Nevertheless, it has not been implemented extensively in developing countries because of the relatively high cost of isolation devices. To reduce manufacturing and assembly cost of elastomeric bearings, fiber-reinforced elastomeric isolators (FREIs) can be used as an alternative to traditional steel reinforced elastomeric isolators (SREIs). Steel shims representing the reinforcement and offering the confinement action in traditional SREIs can be replaced by bidirectional fiber layers in FREIs, and installation can be accomplished by exploiting friction mechanisms and roughness at the rubber-concrete interface, thus avoiding any anchorage bolts (unbonded configuration). In this contribution, experimental dynamic tests on two full-scale circular (diameter 620 mm) FREIs realized with polyester fabric and tested in unbonded configuration are presented. The tests were performed at the EUROLAB of the CERISI, University of Messina, Italy, to investigate the hysteretic behavior under a range of frequencies, axial loads, and amplitudes. The testing protocol, inspired by initial type tests of elastomeric bearings as per European Standards EN15129, included additional 2D tests to investigate the variability of stiffness and damping properties under bidirectional excitation. It has been found that the tested full-scale FREIs exhibit a stable hysteretic behavior and satisfy the main prescriptions of EN15129 standards. However, roll-over phenomena and resulting reduction of contact area under increasing lateral displacements limit the use of these FREIs to within shear strain level of 100%.