Significance of Rotating Ground Motions on Behavior of Symmetric- and Asymmetric-Plan Structures: Part II. Multi-Story Structures

The influence of the ground motion rotation angle on engineering demand parameters (EDPs) is examined in the companion paper based on three-dimensional (3-D) computer models of single-story structures. Further validations are performed here using 3-D models of nine-story buildings that have symmetric and asymmetric layouts subjected to a suite of bi-directional near-fault records with and without apparent velocity-pulses. The linear and nonlinear response-history analyses (RHAs) are used for evaluating the use of fault-normal and fault-parallel (FN/FP) directions and maximum-direction (MD) to rotate ground motions. This study suggests that individual ground motions rotated to MD or FN/FP directions not always provide conservative EDPs in nonlinear range, but often produce larger EDPs than as-recorded motions. In practice, when a suite of ground motions is used, nonlinear RHAs should be performed by rotating them to the MD and FN/FP directions, and maximum response values should be taken from these analyses as design values.