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F. Ziegler, A. Kazemi Amiri:
"Passive Control of Bridge Vibrations by Means of Tuned Liquid Column Gas Dampers";
in: "Proc. 5th European Conference on Structural Control (5thEACS)", issued by: EACS; Erredi Grafiche Editoriali, Genova, 2012, ISBN: 978-88-95023-13-7, Paper ID 034, 12 pages.

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. The evident features of this type of absorbers are no moving mechanical parts, cheap and
easy implementation, low maintenance costs and simple modification of the natural frequency, and even of
the damping properties (by means of built-in orifice plates). Modal tuning in the design stage by means of
the analogy to the classical mechanical damper of the spring-mass-dashpot type, TMD, 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, as worked out in detail, in the case of the cantilever method of
bridge construction, to increase the allowable maximum length of the cantilever, despite of wind-gusts. An
alternative design, VTLCGD provides the control force vertically, and thus counteracts dominating vertical,
traffic-induced vibrations. Sealing of the piping system in that case is a necessary condition since an
equilibrium gas-pressure difference is essential for the vertical action of the displaced fluid. The horizontal
length of this absorber is kept to a minimum. Illustrative examples are described to convincingly approve the
un-revealed action of the liquid absorber.

vibration absorber, horizontal (torsional) or vertical bridge vibration, cantilever method of bridge construction, Den Hartog and state space optimization, robust control.