Low-cost base isolation systems for unreinforced masonry buildings in developing countries

Unreinforced masonry (URM) buildings are one of the most common constructions in developing countries and are usually constructed based on traditional knowledge without engineering intervention. Due to poor seismic performance of URM buildings, the development of seismic protection systems can play a key role in the mitigation of losses in future earthquakes. Despite the availability of different interventions for seismic strengthening of URM buildings, the quest for a cost-effective technique still exits. On the basis of recent outcomes by these authors, this study presents the design of low-cost base isolation systems for a class of URM buildings deemed representative of the building stock of developing countries. The proposed base-isolation system is made by recycled-rubber fibre-reinforced elastomeric isolators (RR-FREIs). Building classes were defined by properly selecting those parameters which are expected to mostly affect the seismic behaviour of the building such as number of storeys, masonry type and in-plan irregularity. Three-dimensional numerical models of URM buildings were developed in SAP2000 using nonlinear layered shell elements and bilinear models for RR-FREIs. Nonlinear time history analyses were carried out for a set of ground motion records to investigate the performance of both fixed-base (FB) and base-isolated (BI) configurations of URM buildings. The comparison of results shows a significant reduction of inter-storey drift ratios for BI configuration, thus demonstrating the effectiveness of RR-FREIs.