Studies On Wind-induced Dynamic Response Of High-rise Lattice Towers

High-rise lattice towers are a special kind of flexible structures because of being hollow-out and high flexibility. It has been widely applied in civil engineering infrastructures such as power transmission, communication, broadcasting television systems and construction phase of large-span bridges. Due to its characteristic of geometrical shape, the dominating load of high-rise lattice towers is wind load. With the growth of demand and progress of technique, it has been developed to be much higher, lighter and softer, intensifying its sensitivity to wind load. Therefore, it is of paramount significance to study the wind-induced dynamic response of high-rise lattice towers.By taking a typical transmission tower in State Grid's 1000kV UHV transmission line as example, the wind-induced dynamic response of high-rise lattice towers is investigated in the present study, and the main contents are as follows:(1) The finite element model of the target tower is established, and the fidelity of this model is validated by analysis. The wind loads acting on transmission tower are digitally simulated by wave superposition method and applied to the finite elemnt model to obtain the structural response in time domain. It is shown that the first mode contributes predominatly the overall response. The variation of structural response of wind velocity and damping ratio is also investigated.(2) The aeroelastic model of the attendant tower is designed and manufactured following similarity criteria. The boundary layer wind is simulated in wind tunnel with passive method. The dynamic response in turbulence flow is measured for a wide range of wind velocity and wind attack (yaw) angle. The experimental results are converted to the real structure according to the required similarity criteria. The RMS of acceleration response are calculated, the rules by which the RMS responses varies with the wind velocity and wind directional angels are analyzed.(3) According to random vibration theory considering a single mode, along-wind gust loading factors for the lattice tower are determined in the frequency domain, the results are compared with those obtained from the time-domain method, wind tunnel testing as well as from the Wind Load Specification for building structures, China. A rough consistency in the results obtained from the time-domain and frequency-domain methods and wind tunnel testing is observed. However, the gust loading factors obtained with Wind Load Specificaiton is considerably larger than the above theoretical and experimental results, and is unsuitable for wind resistant design for transmission line towers. Thus, a parameter of equivalent width of the tower is suggested and is used to determine the gust loading factor, more reasonable results than the original specification is obtained.(4) The effect of turbulence length scale on dynamic response is investigated by using the formula derived from random vibration theory considering the first mode. It is shown that the turbulence length scale has a significant effect on the resonance response and has a noticeable effect on the overall response. Such an effect decreases with the increase of structural damping and the ratio of structural modal frequency to predominant frequency in the wind velocity spectrum. In recognizing that the present wind tunnel testing technique cannot simulate the turbulence length adequately, a set of correction coefficients are developed and may be used when the turbulence length scale is not appropriately scaled in wind tunnel testing.