Mitigation Effect of Vortex-Induced Vibration of Suspension Bridge Hangers with Stockbridge dampers

Abstract

PWS is polyethylene-coated hanger cable that has the advantages of maintenance and durability but because of its smooth surface, it has the weakness of wind resistant performance. This paper tries to supplement wind resistant performance by using Stockbridge damper known for mitigating effect of vibration for a cable. For the design of the Stockbridge damper, a suspension bridge in Korea was selected and one of the hanger cables for the bridge was set up for the target hanger cable. Through wind data obtained from anemometer on the bridge, the target frequency range was determined as 5~20Hz. In order to evaluate the vibration of a hanger cable, Stockbridge damper was modeled as 2-DOF system. For verification of 2-DOF model of Stockbridge damper, excitation experiment of Stockbridge damper was carried out with SB8, SB12 and SB16. Dynamic properties obtained from 2-DOF model were compared with dynamic properties extracted from the experiment and the similar results were obtained. Amplitude of vortex-induced vibration was evaluated by Energy Balance Method with dynamic properties obtained from 2-DOF model and results showed that Stockbridge damper mitigates effectively the amplitude of the hanger cable in the vicinity of its natural frequencies. Based on this, asymmetric Stockbridge damper for the target hanger cable was designed and when designed Stockbridge damper was installed to the target hanger cable, the amplitude of the cable satisfied the allowable amplitude on target frequency range.