SUMMARYA recent trend in the design of base-isolated structures is the extension of the natural period and the incorporation of high damping. This paper shows that the existing simpliÿed methods perform less accurately in this ÿeld of application, mainly due to inappropriate use of spectral data and insu ciently adjusted equivalent models. The paper proposes new period-dependent concepts to reduce pseudo-acceleration spectra and to transform these values into total accelerations with respect to the viscous damping ratio. The model of equivalent damping is adjusted to re ect several period-dependent e ects. The estimation of the accelerations in MDOF systems is based on additional period shifts. All modiÿcations are derived for a simpliÿed linear approach based on eigenforms, and a non-linear approach based on pushover and capacity spectrum analysis. To illustrate observed problems and to demonstrate the capabilities of the proposed concepts, example structures are studied in detail. Furthermore, intensive statistical tests prove the e ectiveness of the modiÿcations in a wide parameter range and show considerable improvements over traditional approaches.

Japan has two decades of experience in designing and constructing baseisolated building structures. Construction has increased significantly since the 1995 Hyogoken-Nanbu (Kobe) earthquake, having reached over 150 annual construction projects. Many new developments and refinements have been made in the material, device, design, and construction of these structures. This paper summarizes recent design and construction of base-isolated building structures in Japan, including statistical data with respect to the common usage as well as the number of new projects.