RESPONSE SPECTRA FOR TWO HORIZONTAL SEISMIC COMPONENTS AND APPLICATION OF THE CQC3-RULE

摘要

This paper aims to: (ⅰ) identify the characteristics of response spectra of the two principal horizontal ground acceleration components for an ensemble of recorded motions, and (ⅱ) show the accuracy of a proposed procedure to use the CQC3-rule in the estimation of critical responses to two horizontal seismic components that may have different spectral shape. The ground motions considered are the ground acceleration records selected in the PEER ground motion workshop (1998). After the two orthogonal acceleration records were rotated along their principal directions, pseudo-acceleration response spectrum was calculated for the major and the minor horizontal components of each event, and mean and smoothed normalized spectra were derived for the ensemble of motions. The normalized spectra are described by typical spectrum curves, but the major and the minor horizontal components have different spectral shapes. The spectral intensity ratio of the minor and the major components is between 0.73 and 0.83 for short periods (less than 0.5 sec.), 0.56 for intermediate periods, and 0.59 for long periods (greater than 2.6 sec.). The smoothed spectra derived above were used to calculate the critical structural response. The CQC3-rule using a constant-spectral intensity ratio given by the average of the two ratios corresponding to the modes with the largest contribution to seismic motion along the x- and y-directions, can be used to estimate the critical response to two horizontal components that have different spectral shapes. Analysis of two multistory buildings indicates that the CQC3 values predict results within 4% of the critical value, pointing out the accuracy of the proposed procedure for determining critical responses.