Vortex-Induced Vibration of Long Suspenders of a Long-Span Suspension Bridge and Its Effect on Local Deck Acceleration Based on Field Monitoring

Abstract

As the main structural component, the possibility of wind-induced vibration, especially vortex-induced vibrations (VIVs), is greatly increased due to the shape and structural characteristics of the long suspenders. To investigate the full-scale wind-induced vibration of the long suspenders of a long-span suspension bridge with a main span of 1418 m, the long-term vibration-based monitoring system was established. Based on the recorded structural health monitoring (SHM) data, the corresponding wind conditions and the vibration characteristics of long suspenders with different diameters and tensions are investigated. Furthermore, modal parameters including frequencies and damping ratios of long suspenders are identified and tracked during the VIV period. The relationship between the shedding frequency of long suspenders and the corresponding wind speed is studied. Results show that the VIVs with frequencies ranging from 8 Hz to 20 Hz were observed continuously across a wide range of wind speeds in both sets of long suspenders. Due to the relatively low modal damping, significant vortex characteristics and lock-in phenomena can be expected on the long suspenders. A new frequency-adjustable Stockbridge damper is employed to suppress multimodal VIVs in the long suspenders. The effectiveness of Stockbridge damper is verified through field application and comparative analysis. Finally, the effect of long suspender VIVs on local deck vibration is discussed, and it is clarified that the bridge deck vibration is mainly caused by multimodal VIVs of the long suspenders, rather than by external loads such as vehicles and wind. The study endeavors to provide a case to progress the identification, assessment, and control of long suspender VIVs in similar long-span bridges.