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A. Kazemi Amiri, F. Ziegler:
"Bridge vibrations effectively damped by means of tuned liquid column gas dampers.";
Asian Journal of Civil Engineering, 14 (2013), 1; 1 - 16.

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, footbridge, den hartog and state space optimization, robust control