Capturing the peak response over all possible orientations for direction of arrival of multicomponent seismic excitation

Abstract

Ground motion is often recommended to be applied with all possible orientations relative to the plan layout of a structure, and the resulting maximum response for an engineering demand parameter (EDP) over all possible directions of arrival (DOAs) is considered in seismic design. The associated DOA is denoted as the critical orientation, which is expected to differ from one EDP to another. A description of the six-component acceleration time series completely defines the required ground motion inputs for most structures. This paper proposes a framework for the maximum response of an EDP over all possible DOAs and the associated critical orientation using three sets of response history analysis of the structure, followed by nominal post-processing. The proposed formulation is “mathematically exact” for linear-elastic systems. A 5- and 30-story reinforced-concrete (RC) building constituted from moment-resisting frames (MRFs) and recorded six-component ground excitations is considered for illustration. Several EDPs are included in this illustration comparing the associated critical orientations, and the resulting variation is significant. The response of an EDP does not significantly change in the vicinity of critical orientation, which, however, is not true at any other arbitrary orientation. Finally, a couple of RC-MRF buildings are considered to understand the variation in critical orientation if the structure is expected to respond in the nonlinear regime. Interestingly, the critical orientation does not alter significantly owing to this inelastic excursion. Based on this limited investigation, the proposed framework may conveniently be incorporated into routine seismic design to account for the maximum direction shaking of multicomponent seismic excitation.