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is perfectly suited to reduce bridge vibrations. If
e.g. the cantilever method of bridge construction
is limited by (wind excited) dominantly horizontal
vibrations a single TLCGD carried along with the
progress of the construction work, can reduce the
vibrations significantly allowing for considerably
longer cantilever arm length. In such an application
vibration measurements identify the permanently
changing bridge dynamics the TLCGD has to be
tuned to the fundamental bridge frequency. The
static pressure head in the gas vessel serves as
convenient frequency tuning parameter for the
TLCGD without changing the geometry or the
effective liquid column length.
For dominating vertical vibrations, e.g. in case
of flexural bridge vibrations, the absorber setup
is modified in the following way: the length B
of the horizontal pipe section is reduced until
the pipe sections are close to each other and one
of the closed pipe sections is charged with static
over-pressure resulting in a static liquid surface
displacement. The remaining small asymmetry
of the liquid filled vertical pipe sections is elimi-
nated by the novel symmetric vertical pipe-in-
pipe TLCGD (VTLCGD), see Figure 8a). The
geometric analogy between the VTLCGD and
the TMD still exists allowing a classical modal
Den Hartog tuning in a first design step, before
splitting the absorber into smaller units in paral-
lel action or considering neighboring modes of
vibration during subsequent fine tuning in state
space. Again, the experimentally observed aver-
aged turbulent damping of the relative fluid flow
and the weakly nonlinear gas-spring render the
THE VERTICALLY ACTING TUNED
LIQUID COLUMN GAS DAMPER
The classical U- or V-shaped TLCGD is perfectly
suited to mitigate lateral or torsional vibrations.
Figure 8. a) Novel symmetric design of VTLCGD for vertical vibration damping, shown with a curved
bottom. B H 1 . Static over-pressure head H 0 indicated in the “equilibrium2” position. b) Dynamic
magnification factor of the vertical deflection at mid-span of a standard 50m-span, SS-steel bridge in
the critical frequency window around the first mode. Single force excitation, (Adapted from Ziegler
(2008)).
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