Improvement of control performance of tuned liquid column dampers in buildings under earthquake excitations

Abstract

In previous research, predication of the natural frequency of tuned liquid column dampers (TLCDs) including a liquid column vibration absorbers (LCVA) is based on the assumption that the liquid velocity within each leg of these dampers is constant and the transition between the vertical and horizontal flows occurs at a single point. This assumption is valid for a TLCD and LCVA when the widths of both the horizontal cross-over duct and vertical columns are small compared to the overall dimensions of the damper. For buildings with limited space, it will be necessary to configure a TLCD with the width of the vertical columns that is not small with respect to the overall dimensions of the damper, a configuration which has not yet been investigated in research. In this case,the variation of liquid velocity in the relatively large transition zone between the vertical columns and the cross-over duct cannot be ignored. A numerical potential-flow method, known as the numerical panel method, is utilized to simulate the velocity distribution of the fluid inside liquid dampers. The method allows an integral equation for the velocity potential to be formulated and solved numerically to determine the flow. These numerical solutions are verified with those obtained from existing experimental results. In addition, three full-scale models of LCVAsare investigated experimentally under free-vibration, spectral and prescribed base excitations. The results from the numerical panel method lead to improved prediction of the characteristics of TLCDs over a wide range of configurations, which is essential in control problems for optimum performance of buildings. The weakness of all passive systems is the inability to provide significant reduction in motion to non-harmonic excitations, such as those encountered when the loadings are of impulsive type. In this case the very first excursion of the building's motion may be the worst in terms of its performance. To improve the TLCD's performance for such earthquake loadings, a TLCD equipped with a flow-triggering device is proposed and investigated experimentally and numerically. The TLCD equipped with a flow-griggering device can keep the fluid in an unbalanced state with a high potential energy. The fluid can be abruptly released at an appropriate time, counteracting the response of the structure induced by the earthquake excitation. It is found that the damping ratio of TLCD equipped with the flow-triggering device tested in this study is higher than typical TLCD. This excessive damping ratio can deteriorate the control performance of the damper. Then, the designed optimum damping ratio is used to simulate in the numerical investigations under various types of excitations, and it is found from the numerical investigations that the performance of TLCD equipped with a flow-triggering device when the damping ratio of the system can be adjusted to the designed optimum value is better than the performance of typical TLCD