Optimal Design Of Energy Dissipation Devices For Structural Vibration Control

Viscoelastic dampers and tuned mass dampers (TMDs) are two commonly used devices for vibration control of engineering structures. The supporting tower of 1000kV high voltage transmission lines are characterized by its height and flexibility, and are therefore vulnerable to wind-induced vibrations; the pedestrian bridges in the urban area may be excited resonantly by the crowd and the issue of user comfort may arise. Based on the structural as well as vibration characteristics of the two kinds of structure, this study aims at developing the customized control methods as well as the optimal parameter design method. The main contents of the works are as follows:(1) A review of structural control technologies and their fundamental theories are presented. The vibration characteristics of the transmission towers and pedestrian bridges are highlighted, and the significance of the study is described.(2) A simplified mathematical model of the damper-brace component is developed and analyzed to obtain the equivalent stiffness and damping coefficients of the component. A mathematical model of tower segment incorporated with damper-brace component is established to derive the modal damping ratio of the tower segment with dampers. The optimal parameters for maximizing the modal damping ratio are obtained, which lay the basis for vibration control of the complete tower. By analog to above analysis of viscoelastic dampers, the optimal parameters for tower segment incorporated with viscous fluid dampers are also obtained. It is found that the maximal damping ratio for tower with viscous dampers is always larger than that for tower with viscous dampers.(3) The optimal parameter design method for vibration control of transmission towers using viscoelastic dampers is proposed. In this method, modal strain energy analysis is first applied to determine the optimal locations of dampers in the tower. The optimal parameters for dampers and supporting brace are determined following the work in (2). It is shown that the locations and damper parameters determined by the proposed method are superior to other cases without parameter optimization, which demonstrates the efficacy of the proposed method. Finally, the buffeting response of transmission towers with and without viscoelastic dampers are compared to validate the control performance of viscoelastic dampers.(4) The application of tuned mass dampers (TMDs) on vibration control of pedestrian-induced vibration on a footbridge is described. Field tests on the control performance of a footbridge retrofitted with tuned mass dampers are conducted, and the damping ratio before and after the installation of tuned mass dampers are obtained. It is shown that the damping ratio of the first vertical mode increase from 1.6% to 4.0% after the installation of TMDs.