Response of Structures under Bidirectional Horizontal Seismic Excitations

Abstract eng:
The Arias intensity tensor is used to define the principal axes of seismic excitation. These axes are employed to characterize the seismic excitations and often interpreted as if their orientations represent the axes of the maximum, intermediate and minimum pseudo-spectral acceleration (PSA) responses. The development of the extended complete quadratic combination (CQC) rule proposed in the literature for evaluating the responses of structures under multicomponent orthogonal seismic excitations and used to select the critical angle of seismic incidence is based on the assumption of the existence of the principal axes. However, the orientation of the axis associated with the maximum PSA response often does not coincide with the orientation of the major principal axis and is period-dependent. The impact of this on the extended CQC rule is unknown and deserves to be investigated. Moreover, to the author’s knowledge, there is no guideline on how to select the magnitude of the response spectra for the two orthogonal horizontal directions that are used with the extended CQC rule. These encouraged us to investigate the accuracy of this rule for estimating the responses under bidirectional horizontal seismic excitations, and their use together with uniform hazard spectra or design response spectrum. The study uses about 600 actual strong ground motion records for such an investigation. The analysis results form the basis for providing recommendations on how to define the spectra for two orthogonal horizontal directions and how to correct the biases in these rules.

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