Using maximum direction of a ground motion in a code-compliant analysis of seismically isolated structures

Abstract

This study investigates the change in response of a seismically isolated structure as a function of ground motion orientation. Accordingly, a ground motion set composed of 11 records was clustered and each record was rotated by 10 degrees increments through 90 degrees. Both the original and rotated forms of ground motion records were scaled in order to perform code compliant nonlinear response history analyses (NRHA). Furthermore, the maximum directions (defined as the direction at which maximum isolator displacements are recorded) of each ground motion record was determined. Then, ground motion records rotated to their maximum directions were also scaled in accordance with code specifications and NRHA were repeated for the same seismically isolated structure. Parallel to code specifications related to the design of seismically isolated structures, averages of maximum isolator displacements (MIDs) and maximum floor accelerations (MFAs) were used to assess the analyses results. It is found that using the maximum direction of ground motions does not provide the maximum response compared to those obtained by considering different orientations of ground motions for both MIDs and MFAs.