Wind Tunnel Tests On Mean Aerodynamic Characteristics For Typical Members Of Lattice Structures

Transmission tower as an important part of electric power transmission engineering,its wind load research has made some achievements,but the theoretical calculation method were all based on the whole-tower model or segmental model of the transmission tower.In the calculation of wind-induced vibration,the wind load are counted as tower segments or structure segments,this method can not directly get internal force or stress of each member in transmission tower.As a result,the theoretical analysis results of transmission towers’ failure or collapse,fatigue,stability and other problems are quite different.For this reason,this paper selected the typical member bar of the lattice transmission tower as the basic research object,through wind tunnel test,the aerodynamic coefficients and interference coefficients of the bars under uniform flow field and different wind deflection angles are obtained,the aerodynamic interference effect between the elements and the calculation method of aerodynamic interference effect in wind load calculation are analyzed.It also provides a research foundation for the subsequent establishment of the local wind load analysis method of transmission tower structure based on the aerodynamic coefficient of independent bars.(1)A set of model support and rotation device for transmission tower which can adjust wind attack angle and wind deflection angle simultaneously is designed,segment models of circular tube and equilateral Angle bar are designed respectively.The aerodynamic coefficients of the single circular tube segment model were obtained by direct force measurement at the wind attack angle of 0°,then the accuracy and rationality of the method are verified by comparison with the value presented in the specifications.(2)The direct force measurement method was used to carry out the wind tunnel test using force balance under the uniform flow field for the typical segment model of a single equilateral angle steel bar.The aerodynamic coefficients of the segment model of a single equilateral angle bar are obtained under the wind deflection Angle of 0°～180°,and the variation curve of the wind deflection Angle of the aerodynamic coefficients of the segment model of a single equilateral Angle bar is obtained.(3)The direct force measurement method was used to carry out the wind tunnel test using force balance under the uniform flow field for two typical circular tube segment model.The aerodynamic coefficients of the two typical pipe segments which are in tandem,parallel or oblique arrangements are obtained,and the database of the aerodynamic coefficients of the two typical pipe segments which are in tandem,parallel or oblique arrangements are also set up(4)The direct force measurement method was used to carry out the wind tunnel test using force balance under the uniform flow field for two typical segment model of a single equilateral angle steel bar.The aerodynamic coefficients of two typical equilateral Angle bars at different intervals under different shielding modes are obtained,and the database of the aerodynamic coefficients of two typical equilateral Angle bars at different intervals under different shielding modes are also set up.(5)Based on the obtained aerodynamic coefficients,the interference coefficients at different intervals under different shielding modes of circular pipe and equilateral angle steel of typical lattice tower members are calculated,and the variation law of the interference coefficients with different intervals under different shielding modes of circular pipe and equilateral Angle steel is analyzed.(6)Presented a method to calculate the resistance coefficient of transmission tower segment based on rod components and verifies the applicability of the method.The results show that as for the two circular tube,the interference coefficient of rod 1 is greater than that of rod 2 in all test interval.With the increase of spacing ratio,the interference coefficient of rod 2 increases gradually,and the interference coefficient of rod 2 becomes weaker and weaker.Under the uniform flow field and different wind speed,the resistance coefficient of single angle steel bar has little change and basically remains stable.Under different turbulivity and wind attack Angle,the resistance coefficient of single Angle steel bar varies greatly.For the two angle bar,the variation law of the disturbance coefficient of bar 2 is basically the same as that of the resistance coefficient under different working conditions of bar1.The interference coefficient of bar 2 gradually increases with the increase of the spacing ratio.It shows that the interference of rod 1 to rod 2 is weaker and weaker.The method of calculating the resistance coefficient of the transmission tower segment based on the rod component shows a small difference from the experimental results.