The Environmental Loads And Ultimate Carrying Capacity Of Large Span Transmission Tower-line System

Large span transmission tower-line system can cross rivers and mountains. The four cross arms on the steel pipe large span transmission tower make the system transfer more power with less area. The tower is so high and the cross arms are so long that the ultimate carrying capacity of the system is different from the normal tower-line system.Wind load, wind drive rain load and ice load are the major environmental loads of the large span transmission tower-line system. One subject of the paper is wind-driven rain load of the tower; another subject of the paper is the ultimate carrying capacity of the tower-line system under wind load.In order to simulate the rain load, first, the fluctuating wind velocity inlet is needed. Based on harmonic wave superimposing method, the time history of fluctuating wind in open site was generated and used as the velocity inlet for flow field simulation. Second, the raindrops must be simulated properly, the fluctuating wind field and raindrops were respectively simulated by detached eddy model and discrete phase model. The rain load is solved at last. According to the impulse equivalence principle, rain load averaged over 0.25s time interval was calculated. The result shows that in all the load case, the biggest ration of rain load to wind load happens when the rain intensity is 709.2mm/h and the average wind velocity is 10m/s at the height of 18m. It's also seen that the ration of the rain load to wind load decreases with height.The other subject of this paper is the ultimate carrying capacity of the tower-line system. The finite element model of a transmission tower-line system is established using ANSYS software. According to the standard of the state, the static ultimate carrying capacity of the system is calculated with four different wind attack angles. The static ultimate carrying capacity of the tower-line system is achieved and the break models of the tower-line system under the different wind attack angles are discussed. The result shows that bottom compressed columns yield first before all the other members. Considering the interrelationship between bending moment and axis stress, the yield load will be smaller. The ultimate carrying capacity of the system at the angle attack of 45 degree is smallest in all load case. The ultimate load is 2.083 times of the design load.The dynamic capacity of the system is studied at last. The dynamic response of the system is calculated under three load cases. The tower-line system breaks when the fluctuating wind velocity reaches 55.1m/s at the height of 10m. The bottom compressed columns are the first members exceed the yield stress.