Field Measurement of the Vibration Characteristics of a Super-Long Hanger of a Suspension Bridge.

Suspension bridge hangers over 100 m are prone to wind-induced vibration. To investigate the vibration characteristics of a suspension bridge hanger over 140 m with two cables on a day affected by typhoon Sura, the field measurement of the wind field and acceleration of two cables at different heights was performed. The wavelet transform method was introduced to analyze the time–frequency characteristics of the hanger and girder, while based on the stochastic subspace identification method, the damping ratios of the hanger were identified. The cluster analysis was performed to investigate the relationship between the wind field and hanger vibration. The result of measurement at the site indicated that under the nonstationary wind, the hanger exhibited three different forms of vibration: vortex-induced vibration, buffeting, and another high-frequency vibration. The first two forms may be caused by the incoming wind, and the last one may be due to the vibration of the bridge deck. The vibration was the same between two cables, but different in multiple heights of a cable. For the same cable, there existed a linear relationship between the in-plane and out-of-plane vibration. The hanger exhibited single-mode and multimode vibrations with an elliptical or eight-shaped motion trajectory. For the multimode vibration, a clear energy alternation phenomenon between the dominant frequency and subdominant frequency was found. The out-of-plane acceleration was greater than the in-plane vibration due to the damping difference in the two directions. The wind field was divided into five clusters, and the clusters of the wind field were related to the mode of hanger vibration. [ABSTRACT FROM AUTHOR]