Experimental assessment and analytical modeling of novel fiber-reinforced isolators in unbounded configuration

Base isolation system is one of the most commonly used technologies implemented around the world for seismic protection of infrastructure. Its objectives are the protection of human life and the reduction of damage to buildings as a result of earthquakes. However, the system is rarely used in developing countries such as Colombia, due to its relatively high costs, including the cost of importing the devices. The development of an isolation system using local technology therefore eliminates the latter expense. This paper focuses on the experimental assessment and analytical modeling of low-cost seismic isolators for low-rise buildings, which represent most construction projects worldwide. Two types of unbonded isolator with a high damping rubber matrix and different reinforcement fibers were employed: carbon and polyester. Scaled prototypes were manufactured and tested under compression and shear loads. Despite the lower mechanical properties of polyester, the results revealed an adequate comparison between the vertical and horizontal properties of the two isolators, with both satisfying minimum required design values. Nevertheless, when taking into account the fact that the price of polyester fiber is one order of magnitude less than of carbon, this seems to be the option with greater potential to be implemented as a low-cost seismic isolation system. Based on the experimental results, an analytical model was proposed to estimate the horizontal stiffness of unbounded isolators, taking into account the reinforcement characteristics, the effective area and the shear modulus of the rubber. In comparison with other formulations, the proposed model was found to be sufficiently accurate to be used in the preliminary design of unbonded fiber-reinforced elastomeric isolators.