Seismic Vibration Control Of Transmission Towers With Nonlinear Pendulum

The power transmission tower-line system, which is the carrier of high voltage power, is an important lifeline project. It is playing an important role in the national economic development. The power transmission-line system is often a high-rise and large-span structure, which is very suspectible to dynamic loads such as earthquakes and winds. Therefore, it is of great research significance and economic values to develop techiques to mitigate the dynamic response of the power-transmission tower, and thus upgrading its reliability and safety.This study aims to suppress the vibration of the power transmission tower structure using the pendulum type dynamic vibration absorbers (DVA). Pounding phenomenon and internal resonance are introduced to the damper to increase the vibration absorbing ability and energy dissipating ability. H∞ norm is adapted to achieve a integraded design of the tower-DVA system. The contents are listed as follows:(1) Spring pendulum is proposed to reduce the vibration of a transmission tower. The kinetic expression of the spring pendulum is obtained through Lagrangian equation. The condition of the internal resonance is verified to be λ=2 using the harmonic balance method. The model of a spring pendulum is established in MATLAB to calculate its response when subjected to an initial displacement. The interanal resonance phenomenon is explained with the assistance of the locus of this spring pendulum. Then, the model of a pratical transmission tower-line system is established to numerically verify the effectiveness of the spring pendulum. Three earthquake records are selected as seismic excitation. The response of the tower is calculated when it is without control, with a classical suspend mass damper and with a spring pendulum. Compared with the suspended mass pendulum, the spring pendulum is more effective in reducing the seismic induced vibration.(2) Impact pendulum is proposed to reduce the vibration of a transmission tower. The major difference between the impact pendulum and a classical suspending mass damper (SMD) is that the tuned mass of the impact pendulum is restricted by a pair of stops. Energy dissipating ability will be increased by collision between the tuned mass and the stops. Introduing the pounding also improves the vibration control effectiveness and the robustness of the impact pendulum. In this study, an experimental study is firstly performed to compare several pounding force model and to estimate the parameters. Then the motion equation of the transmission tower-line system controlled by an impact pendulum is derived. Parametic study is also conducted to investigate the influence of gap, mass ratio and frequency ratio on the vibration control effectiveness. The impact pendulum is also subjected to a fatigue test to investigate its performance when it has undertaken many poundings.(3) A method to achieve integrated optimization of the transmission tower-dynamic vibration absorber (DVA) system is proposed. This method selects the H∞ norm as the optimization objective. Genetic algorithm (GA) is used to find the optimal solution. The multi-degree-freedom model is adapted to simplify the tower when calculating its H∞ norm. In order that the optimized structure satisfied the static loads and that the total mass is not increased, the penalty function is also introduced to adjust the GA fitness. According to the case study, the proposed method further reduced the seismic response of a practical tower, with the static load case satisfied and total mass remains the same. This method avoids calculating the response in the time domain, and thus has high computation efficiency.