Multi-storey structures with compound seismic isolation

Abstract

Seismic isolation, one of the most innovative technologies in the area of performance-based design of buildings, has been increasingly used in the last 15 years worldwide. Seismic isolation is principally based on the incorporation of flexible isolators at the base of a building in order to shift its fundamental period outside the dangerous for the resonance range of periods. In extending the concept of base isolation, the present contribution refers to the control of multistorey structures under earthquake actions by means of introducing seismic isolation at different elevations of the structure. Thus, the structural response is influenced decisively by the vertically distributed seismic isolation, which at the respective storey-levels is alone capable of controlling the partial and overall stiffness, the force transmission and the energy dissipation process of the respective dynamic adaptable system. During moderate earthquakes the seismic isolated structure acts as an absorber of the kinetic energy at the isolation levels, thus minimizing the displacements of the building. During strong earthquakes the effectiveness of the system in further enlarging the period of the building, compared to the classical method of seismic isolation at a unique level, is achieved, most often with decreased inter-storey deflections, and without introducing extensive displacements at the building base, which are often limited by practical constraints. The effectiveness of the proposed control system is investigated in parametric studies, in the time-history range, for a six-storey building under ten earthquakes of the Greek-Mediterranean region. The most effective vertical distribution of seismic isolation at various storey-levels is proposed, based on a multi-criteria analysis of the responses of the isolated systems.