Sealed tuned liquid column dampers: a cost effective solution for vibration damping of large arch hangers

The paper describes the applicability of a sealed tuned liquid column damper (STLCD) for the control of wind induced vibrations of long and slender arch hangers. Such intolerable transverse hanger vibrations were observed on a large railway arch viaduct with hangers up to 35 m in the Netherlands. As a result of a thorough investigation, the vibrations were attributed to unexpectedly low material damping at ζ = 0.0011. A number of possible solutions were investigated, and a final solution with hydraulic dampers was chosen. As an alternative solution for cases such as this, the sealed configuration of a tuned liquid damper may be proposed. The STLCD device allows absorbing the fundamental hanger vibrations, even when exceeding 2.5 Hz. For the aforementioned example, the effect of the STLCD is analysed numerically and tested at reduced scale, indicating that the STLCD satisfactorily increases the material damping of the hangers, excluding the excitation type responsible for the intolerable vibrations. 410 ARCH’07 – 5th International Conference on Arch Bridges Figure 1 : The Werkspoorbridge – side view Consequently, it can only be used for low frequency. However, if the vertical tubes are sealed, a pressure can build up in either side of these sections, increasing the undamped natural circular frequency. Such a device is named Sealed Tuned Liquid Column Damper (STLD). In a first part of this paper, general considerations and calculation related issues on the STLCD concept will be presented. In a second part scale model tests, based on the dimensions of the Werkspoorbridge, are discussed. Finally, practical issues and further research steps are addressed. 2 MATHEMATICAL MODELLING 2.1 Equations of motion When an STLCD is attached to a single degree of freedom structure (Fig. 2), the set of equations of motion can be written as Eq. (1) (Kwok et al, 1996).