Seismic responses of super-span cable-stayed bridges induced by ground motions in different sites relative to fault rupture considering soil-structure interaction

Abstract

The focus of this paper is to evaluate the seismic response of a cable-stayed bridge built in fault zones considering soil-structure interaction (SSI) effects. Bridges crossing fault-rupture zones may be built in the Forward Region (FR), Middle Region (MR) and Backward Region (BR) relative to the possible position of the fault. Three groups of ground motions (51 records in two orthogonal directions) in above regions are selected as the input from the 1999 Taiwan Chi-Chi earthquake based on the sites relative to the fault rupture. The Sutong Cable-stayed Bridge (SCB) is taken as an example. Two models are used in this study, i.e. the fixed-base bridge and the bridge with SSI effects where four different orientation angles (0°, 30°, 60°, and 90°) have been considered compared to the fault direction. Systematic lumped-parameter models are utilized to represent the dynamic behavior of the foundation supported on soil. The results reveal that the seismic behavior of the SCB in those 3 regions shows significant differences. The SSI effects affect the bridge response through a systematic decrease of all modal frequencies and a substantial change in nature of dominant shapes especially for the higher modes of vibrations. The displacement of such bridges may be underestimated if the SSI effects are ignored. The orientation of the bridge axis relative to fault trace influences the seismic responses of the bridges in fault regions. The bridge located in MR experiences larger responses than that in FR and BR. Due to the high values of velocity spectra, velocity-related intensity measures i.e. peak ground velocity (PGV) and the ratio of PGV to peak ground acceleration (PGA) show strong correlation with the seismic responses of the bridge located in FR. Since the records in MR and BR have high acceleration spectra, PGV and PGA correlate well with the responses of the bridge located in MR and BR.