Change in maximum isolator displacements due to change in orientation of scaled near field ground motion records

Abstract

In this study, the change in maximum isolator displacements (MIDs) of a seismically isolated structure is studied as a function of ground motion orientation. The isolator units of the analyzed structure is composed of lead rubber bearings (LRBs). For this purpose, selected as-recorded original forms of ground motions are rotated from 0 degrees to 180 degrees with 10 degrees increments to obtain new records with different orientations. In nonlinear response history analyses, both horizontal components of ground motion records are subjected to structure simultaneously. Employed motions are representative of near-field records and scaled to represent two different seismicity levels namely, design based earthquake (DBE) and maximum considered earthquake (MCE). In the analyses, a deteriorating hysteretic behavior, where the deterioration is a function of temperature rise in the lead core, is used to idealize LRBs. Furthermore, to find the effect of isolation period on this amplification, the isolation period is considered to be a parameter. Thus, four different isolators are designed. The analyses results revealed that the variation in MIDs due to change in ground motion orientation is negligible and approximately equals to 2% in an average sense. Same observation is valid for seismicity levels of both DBE and MCE. Also, isolation period is found to be an ineffective parameter in terms of variation in MID when different orientation of motions is of concern.