DAMPING OF VIBRATIONS – SOME EXPERIMENTAL RESULTS ABOUT TUNED LIQUID DAMPERS

Even in regions with special seismic risk high rises are built. Hereby multiple steps have to be taken in order to construct earthquake proof buildings. One of these steps is the installation of dampers, which reduce the vibrations of the building in the case of an earthquake. Commonly used are so-called tuned mass dampers which consist of a mass-spring system or a pendulum. In recent years also tuned liquid dampers are constructed. In order to learn something about the mode of action of these tuned liquid dampers a testing facility was constructed. The testing facility consists of a concrete plate, which is supported by four steel columns. A movement in one direction is prevented by diagonals at two opposite sides. On top of the concrete plate a rotating mass is located, which rotates with a variable frequency O and causes a vibration of the whole construction. A liquid damper is also located on top of the concrete plate. The hydrodynamic force of the liquid damper acts as a resistance force and the breaking of waves dissipates energy. The force between the liquid damper and the concrete plate and as well the displacement of the concrete plate are measured. Plotting the measured values of the hydrodynamic force and the displacement of the concrete late in the same diagram gives hysteresis loops. The shape of these hysteresis loops gives information about how effective the damper works. With this information the liquid damper can be tuned in a way that vibrations are reduced very effectively. The experiments show that a damper mass of only von 1% of the mass of the building (here the concrete plate) is sufficient to reduce the amplitude of vibrations by 50%.