Response spectra for multicomponent structural analysis

This paper aims to investigate the response spectra characteristics of the principal components of seismic motion, which are required for accurate multicomponent structural analysis. Mean spectra were determined for the three principal uncorrelated acceleration components for an ensemble of 97 earthquake records. The average inclination of the quasi-vertical component from the vertical axis is found to be 11.4 degrees, with a standard deviation of 9.9 degrees. The ratio of the minor and the major quasi-horizontal spectra varies between 0.63 and 0.81, which are lower than the value of I commonly used in design codes. Greater differences are found for near-fault motions in the intermediate-period range. The ratio of the quasi-vertical and the major quasi-horizontal spectra varies between 0.34 and 0.69 for far-fault and between 0.3 and 1.33 for near-fault motions, depending on vibration period. Smoothed spectra of the three principal components that can be used in modern multicomponent structural analysis methods are presented.