Ambient vibration measurements on a cable‐stayed bridge

Abstract

AbstractAn extensive programme of full‐scale ambient vibration tests has been conducted to measure the dynamic response of a 542 m (centre span of 274 m) cable‐stayed bridge—the Quincy Bayview Bridge in Illinois. A microcomputer‐based system was used to collect and analyse the ambient vibration data. A total of 25 modal frequencies and associated mode shapes were identified for the deck structure within the frequency range of 0–2 Hz. Also, estimations were made for damping ratios. The experimental data clearly indicated the occurrence of many closely spaced modal frequencies and spatially complicated mode shapes. Most tower modes were found to be associated with the deck modes, implying a considerable interaction between the deck and tower structure. No detectable levels of motion were evident at the foundation support of the pier. The results of the ambient vibration survey were compared to modal frequencies and mode shapes computed using a three‐dimensional finite element model of the bridge. For most modes, the analytic and experimental modal frequencies and mode shapes compare quite well, especially for the vertical modes. Based on the findings of this study, a linear elastic finite element model appears to be capable of capturing much of the complex dynamic behaviour of the bridge with very good accuracy, when compared to the low‐level dynamic responses induced by ambient wind and traffic excitations.