Three-Dimensional Response Spectra for Multiple-Support Input Motions

Abstract

New response spectra for multiple-support input motions are presented to study the seismic responses of long-span bridges. Three-dimensional response spectra are defined using the response of simple beams with various natural periods. These spectra clearly verify the dominant vibration mode and the critical location of the maximum response. Numerical examples using the earthquake records observed by a newly-installed array at the Akashi Kaikyo bridge construction site in Japan show that the different input motions to each support produce different predominant vibration modes compared with the identical excitation case. It has also been observed that response usually decreases when multiple-support input motions with phase lags are considered. The ordinary response spectra method is also examined and it has been found that the approximated values using the RMS method overestimated the maximum response.