Damping Increase in Building with Tuned Mass Damper

Abstract

The Sydney Tower, the tallest building in Australia, is 820ft (250m) high and with the base of the structure anchored on the roof of a 15 storey building, it stands 1000ft (305m) above street level. The tower is one of the first buildings with the installation of a large scale tuned mass damper (TMD). The doughnut-shaped water tank near the top of the turret, which normally serves as the tower’s water and fire protection supply, was incorporated into the design of the TMD to reduce wind-induced motions. Energy associated with relative movements between the tower and the water tank is dissipated by 8 shock-absorbers installed tangentially to the tank and anchored to the floor of the turret. A secondary TMD of similar design was later installed on the intermediate anchorage ring to further increase the damping level, particularly in the second mode. Full scale measurements were taken to determine the natural frequencies of vibration and damping. Dampings of the tower were determined for different damper configurations. The natural frequencies of vibration were found to be 0.10 Hz and 0.50 Hz for the first mode and second mode respectively. Significant increases in damping levels, particularly in second mode, are produced by the water tank tuned mass damper and the secondary damper.