Seismic response of the superstructure and attached equipment in a base‐isolated building

Abstract Base isolation can be used both to protect the structure and simultaneously to reduce the response of internal equipment. The seismic response of a base‐isolated structure has been studied through the shaking table test or numerical calculation before. The object of this paper is to analyse a base‐isolated structure by a different analytical approach—perturbation analysis. Recognizing that the horizontal stiffness of an isolation system is much smaller than that of the superstructure, the mathematical expressions of the modal properties of base‐isolated structures are derived by the perturbation method in terms of the modal properties of the superstructure and used to study the dynamic response of superstructure and attached equipment in the base‐isolated building. This study shows that the first base‐isolated mode not only controls the superstructural response but also dominates the response of high‐frequency attachment. The contribution of higher modes to the response of base‐isolated structures, which is proportional to the horizontal stiffness of isolation system, is very small.