Development and experimental behavior of HDR seismic isolators for low-rise residential buildings

Base isolation systems reduce the action of earthquakes on buildings by disconnecting the structure from the ground through different devices, being the steel reinforced isolators (SREIs) the most common used. However, due to the high initial costs of SREIs, this technique is mainly implemented in special projects and is rarely used for residential buildings in developing countries with high seismic risk. This paper presented a thorough investigation on novel and unbounded rubber isolators which, based on the satisfactory behavior shown during experimental tests, could be a viable alternative to conventional isolators to be mainly implemented in Colombia for the low-rise residential buildings. Rubber and reinforcement materials employed in the manufacturing of the isolator prototypes were obtained locally to minimize the cost of the new devices. Different isolator configurations, including steel versus nylon/carbon fiber reinforcement (FREI) and bolted versus unbounded connections, were investigated to provide technological competitiveness. In the first phase, a high damping rubber was developed and characterized. In the second phase, prototypes of isolators designed for a real building were built and tested using combined compression and shear test. The results highlight an interesting comparison between vertical and horizontal properties of classical SREIs and unbolted FREIs, both satisfying required design values. Specifically, experimental results show that the behavior of the FREIs, in the horizontal direction, is similar to the SREIs, whereas the damping ratio is higher. Satisfactory results were also obtained with nylon reinforcement. Regarding the connection, the unbonded prototypes showed a better behavior respect to classical SREI, achieving higher deformations without failing. Therefore, this type of unbounded FREIs could represent a very promising option with higher potential to be implemented as a low-cost seismic isolation system in residential low-rise buildings of developing countries.