Seismic fragility of base-isolated single-storey unreinforced masonry buildings equipped with classical and recycled rubber bearings in Himalayan regions

Unreinforced masonry (URM) buildings are one of the most common constructions all around the world, but they are significantly prone to structural damage in case of earthquake. Due to the high vulnerability of URM buildings to seismic loading, a quantitative risk assessment along with identification of additional protection measures has become necessary. Even though base isolation is a suitable seismic protection option, its conventional cost may prevent a wide implementation in developing countries. In this context, this study presents a comparative seismic fragility analysis of a single-storey URM building before and after base isolation using both classical laminated rubber bearings (LRBs) and recycled-rubber fibre-reinforced elastomeric isolators (RR-FREIs). The main aim of the study is to assess the effectiveness of RR-FREIs as alternative to LRBs for seismic vulnerability reduction of low-resistance URM buildings located in Himalayan regions. Fragility analysis accounted for uncertainties associated with both material properties and earthquake records. The Latin hypercube sampling (LHS) technique was used to reduce the computational work while maintaining acceptable accuracy. The building response was obtained using nonlinear layered shell element models, through nonlinear time history analysis of fixed-base (FB) building models and fast nonlinear analysis of base-isolated (BI) building models. Fragility curves show a significant reduction in the vulnerability of BI buildings in comparison to their FB counterpart, as well as a satisfactory performance of RR-FREIs in comparison with LRBs. A parametric study is also discussed to identify the influence of different intensity measures, fragility analysis method, and variability in isolator properties.