Tuned mass dampers for flutter and buffeting control of long-span suspension bridges

The objective of this research is to study the effect of tuned mass dampers (TMDs) on the wind-induced vibration of long-span suspension bridges. Two types of wind-induced vibration phenomena, flutter and buffeting, are considered in this study. Flutter of a long-span bridge is a complex aeroelastic phenomenon which is basically a coupled interaction between the aerodynamic loading and the bridge motion. It is assumed that the bridge vibrates predominately in a torsional mode which is to be controlIed by placing two identical TMDs at the two sides of the bridge cross section where the torsional mode shape is a maximum. These TMDs move in the perpendicular direction relative to the bridge deck which, as a result, generates counteracting torques opposite to the direction of the bridge motion. A set of optimal TMDs' properties, which maximize the critical flutter wind speed of the bridge, are found in closed form by using a frost-order perturbation method. Furthermore, the effect of TMDs on the increase of the critical flutter wind speed is expressed explicitly in simple formulas. The Humen Bridge, a suspension bridge located in the southern coast of China with a steel box deck and a center span of 888 m, is used as an example to demonstrate the effects of the TMDs on its flutter behavior. Also, the control of coupled-mode buffeting response of long-span suspension bridges using two TMDs is demonstrated. It is assumed that the bridge vibrates predominately in the combination of two vertical modes which are to be controlled using two TMDs placed at the two maximum mode shape locations. The TMDs' properties are determined by minimizing the maximum multi-mode buffeting response of the bridge which can be found by using the Optimization Toolbox of the MATLAB program. By neglecting all the modal coupling terms, some simple formulas are derived based on a so-called dual-level pseudo optimal approximation. These formulas provide a quick estimation of the TMDs' properties and can be used as initial values for the optimization routines to reduce the computation time. The Shantou Bay Suspension Bridge located in the southern coast of China is used as an example to demonstrate the control effects of the dual TMDs. The results show that the dual TMDs offer a more effective and more uniform response reduction for a long-span suspension bridge vibrates in multiple modes