Vortex-induced Vibration Generated by Flow Interaction between Two Cable-stayed Bridges in Tandem

Abstract

A vortex-induced vibration (VIV) was observed in the upstream deck of a pair of cable-stayed bridges in 2011. This represents the first case of such an observation in an actual long-span cable-supported bridge in service. The observed VIV was reproduced in a wind tunnel and a series of wind tunnel tests were carried out to identify causes of the VIV. The successful reproduction showed that the VIV was amplified by an interference effect caused by parallel arrangement of decks. An in-depth study was conducted on the interactive vibrations in parallel arrangement. For the VIV, the gap distance between two decks was considered as the key parameter. The considered gap distances covered wide range from one to twenty times of the depth of deck. By variation wind velocity, the amplitudes of VIVs in both decks were estimated. Particle image velocimetry (PIV) tests were also performed to identify the change of streamlines in between two decks for different gap distances. Also the distribution of swirling strength of the generated vortices was evaluated from the velocity data obtained from PIV tests. Alternating eddies were formed in phase with the upstream deck motion and were transmitted to the downstream deck regardless of the gap distances. According to the research results, it can be concluded that the interactive VIV in two parallel cable-stayed bridges is critically affected by the gap distance up to five to seven times of the depth of the deck. This vulnerable gap distance is closely related to the moving distance of one vortex during one-period oscillation of the deck.