Response Spectrum Method for Multiple-Support Seismic Excitations

摘要

A new response spectrum method is developed for seismic analysis of linear multi-degree-of-freedom, multiply-supported structures subjected to spatially varying ground motions. Variations of the ground motion due to wave passage, loss of coherency with distance, and variation of local soil conditions are considered. The method is based on fundamental principles of random vibration theory and properly accounts for the effects of correlation between the support motions as well as between the modal responses of the structure. In the proposed method, the peak response is given in terms of a combination rule involving the peak ground displacements and mean response spectra associated with the support degrees of freedom, and a set of cross-support and cross-mode correlation coefficients that are determined in terms of the individual spectra and the coherency function describing the nature of the spatial variability of the ground motion. Contributions of the pseudo-static and dynamic components of the response, as well as their covariance, are explicitly included in the combination rule. The new method is applied to an example structure with three supports. A comprehensive analysis of the required cross-correlation coefficients is carried out to investigate the influences of the wave passage and loss of coherency effects, as well as the effect of local site conditions.