Passive damping of bridge vibrations by tuned liquid column gas dampers

Sealed tuned liquid column gas dampers, i.e. with a gas spring effect taken into account, TLCGD, are ideally suited to increase the effective structural damping of bridges when vibrating in the critical low frequency band, substituting the classical mechanical damper (TMD). The evident features of TLCGD are no moving mechanical parts, cheap and easy implementation, low maintenance costs and simple modification of the natural frequency (by means of altering the equilibrium gas pressure). Modal tuning in analogy to the classical mechanical damper, TMD, in the design stage is subsequently followed by fine-tuning in state space, rendering the absorber parameter (frequency and damping) optimal and, when designing smaller units in parallel action, yields the control even more robust. The equilibrium gas-pressure is the main control parameter to optimize the absorber frequency when the volume of the individual gas vessel above the liquid-gas interface is properly selected. U- or V-shaped TLCGD with horizontal extension maximized, are proposed to reduce dominating horizontal vibrations of long-span bridges (including pedestrian bridges), and in the case of the cantilever method of bridge construction to allow the increase of the maximum length of the cantilever, despite of wind-gusts. An alternate design, VTLCGD provides the control force vertically, and thus counteracts dominating vertical, traffic-induced vibrations. The horizontal length of the absorber is kept to a minimum. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)