Vibration Excitation and Damping of Suspension Bridge Hanger Cables

Abstract

The paper presents full-scale observations and wind tunnel tests carried out to clarify the mechanisms driving the hanger vibrations observed in the final phases of completing the 1915 Çanakkale suspension bridge. It is found that high frequency low amplitude vibrations were caused by rhythmic vortex shedding whereas large amplitude low frequency vibrations were caused by rain wind galloping. Stockbridge dampers were introduced to mitigate the hanger vibrations but were found to fail due to fatigue of the messenger wire. Taut string theory is reviewed and combined with the wind tunnel test results and damper characteristics to explain the likely cause for damper failure. It is concluded that Stockbridge dampers are well suited for mitigation of vortex induced vibrations if properly designed but are insufficient for mitigation of rain wind vibrations of the hanger cables. Mitigation of rain wind vibrations requires hydraulic dampers connecting the hanger cables to the bridge deck structure.