A Study on Countermeasures against Wind-Induced Cable Vibrations in Cable-Stayed Bridge by Changing Vibration Modes: 2nd Report, Cable Vibration Analyses Taking Account of Gap Effect

Vibrations of stay cables are often induced by wind because of their aerodynamic instability. They must be suppressed to prevent cable fatigue and to allay passenger fear. Although various countermeasures have been developed, totally effective one has not yet been established. The authors have proposed a new vibration reduction method called “Vibration modes changing method” using a permanent magnet. A magnet installed near the end of the cable changes the vibration modes passively by repeating motions of constraining and releasing cables. With this method, growth of the unstable fundamental vibration mode is prevented by dissipating energy of higher stable modes. Comparing with other methods, it is expected to improve low temperature characteristics, maintenance and manufacturing cost. Considering only unstable fundamental vibration modes, the vibration analyses were carried out taking account of gap effects. The results agree well with wind tunnel tests and the design conditions were obtained.