Development of fragility curves for base isolated RC structures

Despite assessing the efficacy of base isolation systems on seismic performance of existing structures in former investigations using deterministic methods, it will be useful to assess the effect of these systems on the structural performance of buildings through probabilistic methods such as developing fragility curves. This study considers three 2-D reinforced concrete moment-resisting frame structures with different heights (3, 7, 12 stories). These structures are rehabilitated using Lead Rubber Bearing (LRB) isolators based on FEMA 356 instructions. Two sets of 7 records including near-fault and far-field records resting on stiff soil are selected to consider seismic uncertainty. Structural uncertainties are considered through modeling different material properties as random variables using Monte Carlo simulation method. Nonlinear time-history analyses will be conducted using open-source platform OpenSees for each level of seismic intensity parameter (here CAV) and using Park-Ang damage index for RC building and shear strain for isolators finally fragility curves are developed. There is a high correlation between CAV levels and mean damage. These fragility curves can be helpful to assess effects of adding base isolation systems in seismic demand of structures in each damage state. Although near-fault earthquakes have high vulnerability on fixed base buildings, their effects on base isolated are more.