Operational field monitoring of interactive vortex-induced vibrations between two parallel cable-stayed bridges

• Mutual interactive VIV was investigated for two parallel cable-stayed bridges.
• Spring-supported section model tests were performed in a wind tunnel.
• The setup damping ratios were estimated by an operational modal analysis.
• The VIVs observed in a wind tunnel were confirmed in field monitoring.
• Wind direction, velocity and duration appear to be the main parameters that affect VIV.

An in-depth study was conducted on interference VIV between two parallel cable-stayed bridges with respect to the mutual motion of both decks downstream as well as upstream. The mechanical damping ratios of both bridges were estimated by the Natural Excitation Technique (NExT) combined with the Eigen Realization Algorithm (ERA) method. The test setup in a wind tunnel takes two wind directions as well as the identified damping ratios of both decks into consideration. The findings, based on parametric wind tunnel tests, suggest that interference VIV is possible, even in the downstream area of the bridge although this has not been reported before. However, the higher lock-in velocity as well as the higher damping ratio of the downstream bridge would be expected to decrease the possibility of VIV. The interactive behavior was further examined using field monitoring data and the results were in good agreement with the findings obtained in wind tunnel tests, in terms of the threshold wind velocity, the frequency components of the motion and the amplitude ratio between the two bridges. Unfortunately, however, a strong wind was not observed opposite to the main wind direction and it was not possible to confirm the interactive behavior for this situation.