可変減衰機構を用いたトラス鉄塔のセミアクティブ制振

Abstract

1. Introduction Application of energy dissipation devices for the passive vibration control of truss towers has been recently researched, because these towers were generally designed to resist wind load. However, as the earthquake load requirements increases, these towers are possibly to be damaged by large earthquakes. On the other hand, researchers have developed semi-active control device that produces any adjustable control force using variable dampers. This paper describes an investigation of applying semi-active control system to truss towers using variable dampers. First, hysteresis of variable dampers is examined using DDOF system. Second, the semi-active control system is applied to the truss towers to confirm the seismic response reduction compared with the passive vibration control. 2. Overviews of control method and analysis method In this study the Maxwell model is used to exhibit variable dampers. Modal control and optimal control theory are introduced to calculate command forces. For variable dampers, the damping coefficient can be adjusted between upper and lower limits to achieve the command forces. Optimal damping coefficients for passive dampers are applied for the upper limit of variable dampers. 3. Semi-active control of DDOF system The hysteresis curves of variable and passive dampers are compared using DDOF system. The shape of a theoretical hysteresis of semi-active controlled SDOF is a rhombus by adjusting damping coefficients of variable dampers. In DDOF system, when the variable dampers are placed at a location close to free end, or mass at fixed end is larger than that at free end, the shape of hysteresis similar to a butterfly. However, variable dampers can dissipate larger amounts of energy than passive dampers. 4. Semi-active control of truss tower structure A truss tower numerical model is created based on an actual telecommunication truss tower consisting of 15 layers. The damper arrangement of variable dampers is basically defined by the optimal locations of passive dampers. The effects of choosing control mode, damper arrangement, the number of dampers and value of maximum damping coefficient on response reduction effect are discussed using the numerical model. 5. Conclusions As a conclusion, the following results are obtained. 1) In DDOF system, when the variable dampers are placed at a location close to free end, or mass at free end is smaller than that at fixed end, the shape of hysteresis similar to a butterfly. However, variable dampers can dissipate larger amounts of energy than passive dampers. 2) In the case of truss tower, peak displacement of semi-active control is less than passive control by using only 1st mode as the control mode. However, then peak acceleration of semi-active control is higher than that of passive control at lower layers, because of adjusting damping coefficients of variable dampers. 3) When the variable dampers are installed at the optimal locations of passive dampers, the displacement response of the semi-active control is smaller than that of passive control. The effect of semi-active control on the displacement reduction increases, as that of passive control decreases. 4) The effect of semi-active control on response reduction is more significant compared to passive control as the number of dampers decreases. 5) The optimal damping coefficient of passive dampers provides the least displacement response in passive control. On the other hand, for semi-active control, the displacement response becomes smaller as the upper limit of damping coefficient of variable dampers increases.