Influence of isolator characteristics on the response of base-isolated structures

The influence of isolator characteristics on the seismic response of multi-story base-isolated structure is investigated. The isolated building is modeled as a shear type structure with lateral degree-of-freedom at each floor. The isolators are modeled by using two different mathematical models depicted by bi-linear hysteretic and equivalent linear elastic–viscous behaviors. The coupled differential equations of motion for the isolated system are derived and solved in the incremental form using Newmark’s step-by-step method of integration. The variation of top floor absolute acceleration and bearing displacement for various bi-linear systems under different earthquakes is computed to study the effects of the shape of the isolator hysteresis loop. The influence of the shape of isolator force-deformation loop on the response of isolated structure is studied under the variation of important system parameters such as isolator yield displacement, superstructure flexibility, isolation time period and number of story of the base-isolated structure. It is observed that the code specified equivalent linear elastic–viscous damping model of a bi-linear hysteretic system overestimates the design bearing displacement and underestimates the superstructure acceleration. The response of base-isolated structure is significantly influenced by the shape of hysteresis loop of isolator. The low value of yield displacement of isolator (i.e. sliding type isolation systems) tends to increase the superstructure accelerations associated with high frequencies. Further, the superstructure acceleration also increases with the increase of the superstructure flexibility.