Mitsuo Miyazaki and Yukihiro Nishimura

Abstract:
Seismic isolation can provide superior building safety and dynamic performance during strong earthquakes, however, it is known that some near-source ground motions produce excessive response deformations, which may be larger than the allowable capacity of the isolation devices. Isolation systems with longer periods and higher damping are more capable of resisting such deformations, and the author proposed new isolation systems with periods of 10 sec, or even longer. Longer isolation periods, however, mean less resistance and restoring force in the isolation systems, which may cause concerns about unstable response characteristics during strong earthquakes. One such unstable behavior is the possibility of excessive horizontal displacements of the isolation system resulting from ground inclination. Based on numerical analyses using existing vertical ground motion records, this paper estimates the ground inclination during earthquakes and studies the anticipated horizontal deformation of isolated structures that might be induced by such ground inclination.

Keywords: seismic isolation, strong earthquake record, vertical ground motion, ground inclination, horizontal response displacement