Application of a 240 metric ton dual-use tuned mass damper system

Abstract

The slender design of a 240 m tall tower structure requires additional structural damping to reduce vortex shedding induced vibrations. Wind tunnel tests indicate that wind speeds can produce critical accelerations at the observation deck on the tower’s top level. The resulting displacements not only give concern regarding fatigue initiation at the concrete core of the tower, but would also lead to the discomfort to its visitors. To mitigate critical displacements a state of the art passive Tuned Mass Damping (TMD) system was chosen to be implemented. The primary use of the tower is not only to give visitors access to the observation deck but to serve as a test facility for equipment susceptible to building sway. To tests the equipment under real life conditions the TMD system is required to be either in passive mode or to artificially excite the tower in its fundamental mode of vibration and cause a significant controlled building sway in a defined direction. To satisfy these requirements a novel dual purpose active/passive TMD system was developed. This hybrid TMD is capable of suppressing the occurring vibration in one direction while with the aid of a control algorithm excites the tower’s perpendicular direction. The following paper reports the design approach of the passive system and describes the control algorithm when switched into active mode. The initial optimization approach will be presented as well as in-situ results of vibration tests and a monitoring campaign of the tower. In addition the safety concept to avoid excessive displacements of the tower will be presented.