Field monitoring and validation of vortex-induced vibrations of a long-span suspension bridge

To investigate full-scale wind-induced vibrations of a long-span suspension bridge with a central span of 1650 m, a long-term wind and wind effect monitoring system was created. The basic wind field characteristics along the span-wise direction of the investigated bridge were analyzed. It was found that the wind field along the span-wise direction was inhomogeneous. The full-scale wind pressure distribution around the lower surface of the twin-box girder was also obtained. From the power density functions (PSDs) of the fluctuating pressures, the vortex shedding frequency of the full-scale twin-box girder was determined. A field visualization test was performed, and the flow pattern around the lower surface was obtained. Thirty-seven vortex-induced vibration (VIV) events were observed during the monitoring period. The corresponding wind conditions and vibrations were analyzed in detail. In addition to the wind direction and inflow turbulence, it was found that the inhomogeneity of the wind field along the span-wise direction of the bridge is also a critical factor that affects VIVs of full-scale bridge. The VIVs from a section model test and the full-scale bridge were compared, and it was found that the vertical VIV amplitude of the section model was much smaller than that from the field monitoring results. Moreover, torsional VIVs appeared in the section model test, whereas it was not observed in the full-scale bridge.