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Tuned liquid column gas dampers (TLCGD) show excellent energy and vibration absorbing capabilities appropriate for earthquake engineering. The objective of this work is to introduce a new concept of coupled tuned liquid column gas dampers which allow an extended field of applications. In the proposed configuration, several absorbers are connected in a spatial chain generating a multi-degree of freedom damper system which can be tuned to a selected number of structural modes. Because all absorbers vibrate at different natural frequencies simultaneously, the proposed design represents an improvement over conventional TLCGD which can only be tuned to a single structural mode. Another benefit of multi-mode tuning is the significant increase in active liquid mass compared to other damping devices. For a most effective vibration reduction, a numerical tuning process in state space will deliver the free system natural frequency and damping ratio of all absorbers. The capabilities of the new damping device are demonstrated on a simple laboratory structure that is investigated numerically and experimentally. The results illustrate the excellent energy dissipating properties of the proposed setup and emphasize the adequacy of coupled TLGCD for base-isolated structures. A notable benefit of such types of dampers lies in their lack of moving mechanical parts, their cheap and easy implementation into civil engineering structures and low maintenance costs. Possible modifications with respect to natural frequency and even of the damping properties can be performed with little additional expenses, and the additional weight due to the liquid mass may be used as a possible reservoir, e.g., for fire fighting. Apart from that, they exhibit a performance that is comparable to tuned mass dampers.

The excessive lateral vibrations of Londons Millenium Bridge and the Toda Park Bridge in Japan due to a large number of crossing pedestrians have raised an unexpected problem in footbridge constructions. Secondary tuned structures, like the conventional tuned mass damper (TMD) or the tuned liquid damper (TLD) were installed to the bridge in order to suppress these vibrations. In the present investigation it is proposed to apply the more efficient and more economic tuned liquid column damper (TLCD), which relies on the motion of a liquid mass in a sealed tube to counteract the external motion, while a built-in orifice plate induces turbulent damping forces that dissipate kinetic energy. For optimal tuning of TLCDs the natural frequency and equivalent linear damping coefficient have to be chosen suitable, likewise to the conventional TMDs, as given in Den Hartog [1]. The advantages of TLCDs are: simple tuning of natural frequency and damping, low cost of design and maintenance and a simple construction. A mathematical model of a three degree-of-freedom (DOF) bridge coupled with an optimal tuned TLCD is derived and analyzed numerically. Furthermore, a small scale experimental model set-up has been constructed in the laboratory of the TU-Insitute. The experimental results are in good agreement with the theoretical predictions and indicate that TLCDs are effective damping devices for the undesired pedestrian induced footbridge vibrations. Mathematical ModelThe equations of motion for the complex hybrid bridge/TLCD system are derived by a substructure synthesis method, which splits the problem into two parts. Thus, the TLCD is separated from the bridge and considered under combined horizontal v t , vertical w t and rotational ϕ t excitations. Applying the modified Bernoulli equation along the relative non-stationary streamline in the moving frame and in an instant configuration, which is given in Ziegler [2, p. 497], yields the nonlinear, parametric excited equation of motion of the TLCD,where a A,x =ẅ t cos ϕ t −v t sin ϕ t and a A,z =ẅ t sin ϕ t +v t cos ϕ t denote the horizontal and vertical acceleration of the reference point A projected to the moving reference frame. Ω =φ t andΩ =φ t define the angular velocity and angular acceleration. The undamped circular frequency of the TLCD in case of an open pipe system is given by ω A = 2 g sin β/L ef f , where g is the gravity constant, β is the opening angle of the inclined pipe section and L ef f = 2H + B in case of constant cross sections. Furthermore, in Eq.(1) the geometry dependent factors are given by, κ = (B + 2H cos β)/L ef f , κ 1 = 2H sin β/L ef f and κ 2 = (B cos β + 2H)/L ef f , where B and H are the horizontal length of the liquid column and the length of the liquid column in the inclined pipe section at rest. The head loss coefficient δ L due to turbulent losses along the relative non-stationary streamline can be controlled by the opening angle of the built in orifice plate. Eq.(1) is nonlinear due to turbulent damping of the fluid motion, which is consider...

Tuned liquid column damper (TLCD) show excellent energy and vibration absorbing capabilities appropriate for applications in wind- and earthquake engineering. The objective of this chapter is to demonstrate the outstanding features of the proposed Tuned Liquid Column Gas Damper (TLCGD) and present its wide spectrum of applications of three design alternatives. Among others it includes base isolation of structures, applications to lightly damped asymmetric buildings and other vibration prone structures like bridges (even under traffic loads) and large arch-dams as well as simple, ready to use design guidelines for optimal absorber placement and tuning. The evident features of TLCGDs are no moving mechanical parts, cheap and easy implementation into civil engineering structures, simple modification of the natural frequency and even of the damping properties, low maintenance costs, little additional weight in those cases where a water reservoir is required, e.g., for the sake of fire fighting, and a performance comparable to that of TMDs of the spring-mass- (or pendulum-)-dashpot type.