Study On Wind-induced Response Of Lattice Transmission Tower And Transmission Tower-lines System

Since transmission tower-line system is characterized by lightweight, tall, flexible, long-span and low damping, it is very sensitive to wind load. The wind-induced disasters in transmission tower-line system occur frequently. At the present time, the specific wind resistance design method for lattice transmission tower and study on wind-induced responses of transmission tower-line system are still in the process of research and there is not a well-known, effective and specific wind resistance program. Moreover, the exciting mechanism of cross-wind vibrations of lattice transmission tower are also in the explore stage and not be confirmed thoroughly.In this thesis, a theoretical deficiency inherent in the current formula for calculating generalized aerodynamic force spectrum is improved and the wind tunnel tests of the aeroelastic models for three typical lattice transmission towers are performed. In order to provide a practical, convenient and feasible program including the specific parameters, investigations on the exciting mechanism of cross-wind vibrations, wind loading model, model for calculating wind-induced displacement response including higher modal contributions, new approach for calculating wind-induced internal forces of tower and so on are systematically processed. Moreover, the reasonable subject investigated of transmission tower-lines system is selected through test analysis in order to get more reasonable analytical. results of middle tower(aeroelastic tower). Finally, the wind-induced responses are investigated and some regularity test results are firstly addressed. The main works are summarized in the following:(1) The theoretical deficiency inherent in the current formula for calculating generalized aerodynamic force spectrum is explicitly point out and improved. The correlation between input and output is sufficiently considered and the specific inducing process and improved formula are given explicitly. Then, it explains and emphasizes that the influence of aerodynamic damping force,in actuality, has been included in the formula. So, it is not necessary for the influence to evaluate the aerodynamic damping specially.(2) Intensive investigations and studies on the exciting mechanism of cross-wind vibrations are performed. It explicitly points out that the high-frequency vortex shedding does exist but its contribution to wind-induced displacement response is small and might be ignored. Then, the investigations on the reason of cross-wind vibration are intensively and comprehensively performed and the results show that it is a large-scale wake flow generated in the process of interaction between wind and transmission tower induces tower's cross-wind vibration. The research result, in terms of conclusion, confirms the analysis result given by Dr. Zou Lianghao. Moreover, by comparing the test results obtained from uniform flow field and turbulent flow field, it points out that it is the fluctuating components, instead of the mean components, of turbulent flow field that generate the large-scale wake flow mentioned above,. The conclusion makes more progress for understanding the exciting mechanism of the cross-wind vibration.(3) A new approach to solve the internal forces of frame member of transmission tower is presented, and the calculating model of wind load and fomula for displacement response are separately deduced as well.. Based on the improved formula of fundamental mode generalized aerodynamic force spectrum and the results of wind tunnel test in this thesis, a practical model for calculating fundamental mode generalized aerodynamic force spectrum is established, and the corresponding fitting parameters and RMS deviation coefficients of generalized aerodynamic force are also given. Then, two new variables, location matrix and generalized aerodynamic force spectrum mode coefficient, are firstly defined, and a model for calculating higher mode generalized aerodynamic force spectrum in along-wind direction is further derived. Furthermore, a practical model for calculating alongwind-induced displacement response, including the contribution of higher modes, is deduced. Finally, a new approach named "applying load using displacement" is presented and proposed to solve the internal force of tower. The method is not only rational and feasible, but also avoids establishing the equivalent static wind loads.(4) Intensive test investigations on the wind-induced response of middle tower of transmission tower-lines system are performed and some new discoveries about the corresponding regularity are firstly addressed. It point out that it is necessary to select the system including five tower and four line segments as system investigated in order to get more reasonable test results. The influence of wind velocity and sag on along-wind and cross-wind displacement responses is investigated and analyzed comprehensively. Besides, the power spectrums of displacement responses in along-wind and cross-wind direction are further analyzed and it discovers some new phenomena which are not addressed in previous literatures. According to the phenomena, the rational explanation and further inference are given. Moreover, the plane and space motion path of displacement response under different wind velocity are also given. Through further analysis, the uniform variation regularity of the motion path, with the increase of wind velocity, is discovered and firstly addressed.