Study on reduction of vibration control devices for Akashi-Kaikyo Bridge

The Akashi-Kaikyo Bridge is a suspension bridge with a main span of 1,991m. Since the towers have the height of 287m, they could suffer out-of-plane deformation due to vortex induced oscillation even after completion of the bridge. Therefore a cruciform cross-section, which has excellent aerodynamic stability, was selected for the tower shafts and tuned mass dampers were installed in each tower shaft as vibration control devices. Furthermore, additional dampers were installed between the tower and the girder for double safety, because the towers are the most important structure of the suspension bridge. According to the monitoring data, it has been found that recorded vibration amplitudes of the tower shafts were very small compared with design values. It indicated that some of the vibration control devices may be unnecessary. Although the vibration control devices have to be maintained in good condition, it has been demanded that expenses for their maintenance be reduced. Therefore the authors started to study damping performance and allowable vibration amplitude of the tower, in order to make some of the devices unnecessary. After safety of the bridge will be confirmed without some devices, maintenance costs will be reduced.