Effects of ground motion spectral shapes on the design of seismic base isolation for multi-story building according to Eurocode 8

Seismic isolation bearing has been considered an effective solution for constructions in earthquake areas. However, the isolator design criteria are strongly depended on the earthquake properties, especially the spectral shapes of ground motions. This paper presents the seismic responses of isolated building structures affected by earthquakes with different spectral shapes as per the specification of Eurocode 8 (EC8). The equivalent bilinear model is used for addressing the seismic behaviour of isolators. A parametric study presents a simplified estimation procedure for seismic responses of isolated structures and isolator’s properties by using the single-mode spectral analysis approach performed on an equivalent simplified model of isolated buildings. Numerical analyses are conducted on three-dimensional models of a typical multi-story building to study the impact of spectral shapes on the seismic responses and the design requirements of isolated structures. Nonlinear time-history analyses are carried out using Etabs software, where the historical seismic records used for modelling have been scaled to match the target spectrum according to EC8. The results show that the seismic spectral shapes have significant effects on the seismic demands of isolated structures and the isolator’s properties, especially the initial characteristic strength Q. The seismic performance requirements of isolators, particularly the energy dissipation capacity, for type I spectra are significantly higher than for type II spectra. Furthermore, isolators designed for type I spectra provide an over-efficient and are considered to be inappropriate for the structures located in earthquake regions with type II spectra.