Variation of Damping Reduction Factors Used in Design of Isolated Structures Due To Ground Motion Directionality

Abstract eng:
In seismic isolated structures, the level of equivalent damping ratio is generally greater than 5%. However, the elastic design response spectrum provided by codes specifications are for 5% critical damping. Thus, it has to be modified so that the effect of high damping can be considered. This is achieved by using damping reduction factors. In this study, variation in damping reduction factors due to ground motion orientation has been investigated. Accordingly, orthogonal horizontal components of selected as-recorded ground motions were rotated from 0o to 180o with increments of 10o to mimic various ground motion orientations. Then, damping reduction factors of all the rotated records and the original ones were computed for various damping ratios. Computed values are used to assess the amount of variation in damping reduction factors as a function of ground motion orientation. Results of this study indicate that ground motion orientation is a significant parameter in computation of damping reduction factor.

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