Optimal design of pure-friction isolators with and without restoring device: A multi-objective cuckoo search-based approach for seismic-excited structures

Abstract The present study addresses the optimal design problem of pure-friction isolators with a restoring device for seismic-excited structures. A multi-objective cuckoo search-based design approach is proposed to create a suitable balance between the conflicting objectives i.e. the reduction of base displacement and superstructure accelerations. Numerical studies are carried out on three structures with 4, 8 and 12 stories. Sixteen performance indices related to the root mean squares (RMS) and maximum seismic responses of the isolation system and superstructure, and the maximum energy responses of the superstructure are defined for evaluation of the proposed optimal design approach. For comparison purposes, the optimal design approach is applied for the corresponding pure-friction isolated structures without the restoring device. For seven earthquakes considered in this study, the simulation results show that the pure-friction systems significantly mitigates the seismic responses and maximum input and damage energies entering to the superstructure. Furthermore, equipping the pure-friction isolation system with the optimized restoring device may result in a moderate increment in the superstructure responses. Nevertheless, the given responses are significantly less than the responses of the corresponding fixed-base structures. At the cost of increasing some seismic responses due to the use of the restoring device, important advantages are given in terms of significant reduction of the base displacement and eliminate their residual displacement. It is also found that the seismic performance of the pure-friction isolation systems, in both cases, often decreases by increasing the number of stories.