A Study on the Response Instability of Seismically Isolated Structures Affected by Ground Inclination During Earthquakes Part 2 : Influence of Dynamic Ground Inclination

Abstract

In the design and analysis of seismically-isolated structures, it is assumed that the ground is always horizontal during earthquake ground shaking. But a previous paper [3] found that ground inclination may reach to 1/1000∼1/100 (rad) during earthquake shaking, and that the horizontal displacements of isolated structuresmay be significantly affected by the static ground inclination. This paper investigates how the displacement of isolated structures may be increased by dynamic ground inclination during earthquake shaking. Since no time-histories of ground inclination exist, this paper assumes two different conditions for ground inclination motions : sine-wave motions, and displacement time-history inputs with the same phasing as vertical displacement waves. In the case of assumed sinewave motions, the increased displacement of an isolated structure due to dynamic ground inclination can be predicted by considering two factors: the basic increase displacement and the resonance amplification ratio of the isolation period to the dynamic ground inclination period. When displacement time-history waves are considered, the upper limit of displacement increase can be predicted by the isolation period and the longest period of the ground inclination motion.