Study On Wind Loading And Wind-induced Response Of UHV T-shaped Transmission Tower

With the improvement of the State Grid construction,the Ultra High Voltage(UHV)grid has become the main mode of power supply,which is currently in the stage of vigorous promotion in China.So it is very important to study T-shaped transmission towers for UHV transmission lines.Wind load is the main control load of transmission towers.Because of the characteristics of long cross-arms and complex shapes,T-shaped transmission towers have the first-order torsional mode,which means that wind-induced torsional effect is significant.Therefore,it is very necessary to study the wind loading and wind-induced response of T-shaped transmission towers.The complicated model and simplified model of T-shaped transmission tower are established.The wind-induced response of transmission tower is studied and analyzed by time domain method and frequency domain method.The results show that the first mode of T-shaped transmission tower is torsional mode.The wind-induced responses of the two models are close.Under symmetrical and asymmetrical loads,the wind-induced responses of long cross-arms and sheep horns have obvious changes.The main member of the tower mainly bears the influence of bending moment,while the diagonal member of the tower mainly bears the torsion moment.Under uniform flow and terrain B wind field,the high frequency force balance tests on T-shaped transmission tower are carried out.The results show that the along-line drag coefficient of the whole tower reaches its peak value at the wind direction angle of 10 to 15 degrees.The torque fluctuation drag coefficient will be larger with the increase of cross-arm length of the transmission tower,while it will decrease with the increase of the wind direction angle.Based on the test data,the calculation methods of equivalent wind loads in Y direction,X direction and torsion direction are proposed.Based on top displacement,base shear force and base bending moment,equivalent wind loads and overall wind-induced vibration coefficients of the whole tower are obtained.The aeroelastic model of T-shaped transmission tower is tested in wind tunnel,which is aimed at measuring the acceleration and displacement responses under different wind speeds and wind downwards.The results show that the displacement and acceleration responses of transmission towers increase with the increase of wind speed.The transverse wind-induced vibration effect can not be neglected.Based on the wind tunnel data of six test wind speeds,the wind-induced response and wind-induced vibration coefficients at 43m/s design wind speed are obtained by fitting.The results of displacement and acceleration responses are similar to those of numerical simulation,The wind-induced vibration coefficients obtained by numerical simulation are larger.,while the calculation results of the three codes are conservative.The wind tunnel test of terrain model is carried out for a complex hill.Under different mountain wind conditions,the wind loads and wind-induced responses of T-shaped transmission towers are compared.The results show that there is a significant acceleration effect at the top of the mountain at all wind directions.There is no acceleration effect at the canyon position.There is a certain acceleration ratio at the hillside and foot position in the cross wind direction.At the top of hill,the average displacement of the transmission tower top from wind tunnel tests increases about 55%relative to the flat terrain.The calculation results in the Chinese and European codes are conservative.The stress of the main member of the tower increases most obviously and it will decrease with the increase of height.The stress of the main member of the tower head shows the law of small end and large middle along the transverse direction.