In this paper, a multi-objective optimization for the optimal design of sliding isolation systems for suppression of seismic responses of building structures is presented. Due to the presence of several parameters affecting the performance of sliding base isolation systems, applying a rigorous multiobjective optimization technique is inevitable. Hence, in this study, the genetic algorithm is used to find optimal values of isolator parameters, including coefficient of friction, mass of base raft

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... and the damping ratio of the restoring force device. The restoring device, which is composed of a linear spring and a linear viscous damper, is attached to the base raft in order to minimize the during-event and after-event sliding displacement of the base raft. The simultaneous minimization of the building's top story displacement and its acceleration, and also the base raft's displacement, are considered as the objective functions. In order to satisfy the objective functions, a fast and elitist Non-dominated Sorting Genetic Algorithm (NSGA-II) is used to find a set of Pareto-optimal solutions. The isolated building is modeled as a shear-type structure having one lateral degree of freedom at each story level. A ten-story building is used for the numerical study and an ensemble of seven earthquake records is considered for the analysis. The results indicate that by applying the final design parameters obtained from the optimal values found by the NSGA-II approach corresponding to each individual record, the sliding isolator system effectively suppresses the structural seismic responses. Also, it is found that the restoring device with an optimal viscous damper might slightly reduce the performance of the isolation system, but is strongly effective in controlling the maximum base raft displacement and the residual base raft displacement. (N. Fallah). reduce the structural response during the seismic strong motion and ensure minimal damage to structural systems. The seismic isolation system is a passive structural control, whose operation does not rely on external energy sources. Vibration isolation is globally recognized as an effective technology to reduce the seismic effects on strategically important structures such as hospitals, schools, bridges and nuclear power stations. The structure is decoupled from the horizontal components of the ground motion by mounting base isolation between the building and its foundation. Different types of isolation system have been proposed by researchers, where their common features; are horizontal flexibility and energy dissipation capabilities. The horizontal flexibility provides a natural frequency shift to a lower value and away from the dominant energy containing frequencies. The most popular types of base isolation are Laminated Rubber Bearings (LRB) and sliding bearings. A state-of-the-art review of building base isolation is presented by Jangid and Datta [1], and Peer review under responsibility