Seismic isolation is an efficient method for improving the seismic behaviour of building structures. Sensitivity analysis of the behaviour of base-isolated structures is essential for investigating the effects of various mechanical and environmental factors on the performance of seismic isolation systems. In this study, the optimal design of a lead-rubber-bearing seismic isolation system was investigated by considering irregular mass conditions and near-fault seismic excitation. The grasshopper optimisation algorithm was used to optimise the design of the isolation system. Sensitivity analysis of the seismic response of the isolated structures was carried out for the mechanical parameters of the isolation system, mass irregularity in the building and near-fault earthquakes. The results proved the efficiency of the algorithm in optimal design problems for structural isolation systems. Also, the sensitivity analysis of the seismic behaviour of base-isolated structures showed that the yield base shear index had the most important effects in analysis. Furthermore, mass irregularity showed a negligible influence on the behaviour of the isolated structures.
