Vibration Properties Of Rectangular Tuned Liquid Dampers With Submerged Nets And Its Application To Structural Vibration Control

The application of high strength, lightweight materials as well as development of design methods has created the modern bridges with larger span, higher flexibility and less damping, which intensifies the vulnerability of bridges to wind, seismic and pedestrian-induced loading. Excessive vibrations may cause the user discomfort, structural fatigue and endanger the structural safety in severe situations. Development and application of tuned liquid dampers(TLD) have been always regarded as leading research topic in the field of wind resistance and seismic resistance of long-span bridges. Due to its advantages of low cost, convenience in implementation, multiple-directional control, easy activation in small excitation amplitude, tuned liquid dampers have been applied in high-rise buildings for vibration attenuation. However, liquid sloshing in rigid tank has strong non-linear characteristics which mainly depend on base excitation amplitude and excitation frequency, which results in the mathematical modeling of TLD being quite complicated. In this paper, dynamic characteristics of TLD with and without damping screens are both studied, then the TLD is installed in a footbridge for lateral vibration reduction which verify that it has an excellent performance in vibration attenuation. The main contents of this paper are listed below:(1) Firstly, the equivalent non-linear stiffness and damping model(NSD model) for TLD with pure water and the influencing factors of its modal parameters(non-linear stiffness and damping) are reviewed. Then the equations of motion for the structure-TLD system based on the NSD model are formulated following the NSD model, the displacement dynamic magnification factor( DMF) for the main structure subject to harmonic excitation is obtained. The optimum parameters of TLD which minimize the maximum value of DMF are numerically obtained. The control performance of TLD is experimentally assessed with shaking table tests of an in verted pendulum structure equipped with TLD. The lateral steady-state displacement response of the main structure under various excitation frequencies near that of the first lateral mode is measured. The experimental results validate the control efficiency of TLD with parameters determined from parametric optimization.(2) The characteristics of TLD with damping screens are studied for the purpose of solving the strong nonlinearity due to the low damping of pure water. Shaking table experiments for TLD equipped with and without damping screens is carried out. The dimensionless wave height of side wall in TLD under various excitation frequencies with different value of parameters, such as the excitation amplitude, number of damping screens, location and blocking ratio of damping screens and so on is measured. Results show that the non-linear characteristic of TLD equipped with damping screens decrease significantly and the non-linear characteristics such as the phenomenon of ‘jumping frequency’ and ‘frequency shift’ existed in pure-water TLD is avoided. The equivalent tuned mass damper of TLD with damping screens is derived and the equivalent mass, equivalent stiffness and equivalent damping which changes depend on excitation amplitude are also obtained following the wave theory. The optimal parameters of TLD with damping screens are obtained by optimizing the response of TLD equipped with screens-main structure system.(3) The finite element model for a suspension footbridge located in tourist area is established and the dynamic properties such as modal shapes, modal frequency and modal mass are acquired. The human-induced vibration of the footbridge is analyzed with two pedestrian load models, namely the equivalent harmonic load model and random pedestrian force model. Parametric optimization and location selection of TLD is carried out for the purpose of controlling lateral vibration of this pedestrain bridge. Finally, the effectiveness of TLD on controlling footbridge ’s vibration is verified by analyzing the lateral acceleration response of footbridge with and without installing TLD under the action of two kind of load model.