Experimental Study Of Mechanical Properties For Transmission Tower Materials At Low Temperature

Low temperature will affects the mechanical properties of angel steel transmission tower.As the temperature decreases,the ductility and toughness of the steel will continue to deteriorate,which may easily lead to brittle fracture accident of tower materials.Angle steel leg member is the major stress components of transmission tower.Once the leg member brittle failure occurs,it will endanger the operation of the transmission line and the entire power system.However,it is not sufficient that the research of the failure mechanism and process about transmission tower bolt joint at the low temperature.Therefore,studies of mechanical property about transmission tower steels and bolted joints in low temperate,to propose the principle of selection of tower materials,are of great significance to ultra high voltage transmission line.In this paper,on the one hand,the low temperature uniaxial tensile test and Charpy impact test are conducted to investigate the low temperature mechanical properties of Q345 B and Q420 C angle steel as well as its welded joint with various thicknesses.And the effects of low temperature on mechanical properties of angle steel are presented.On the other hand,the full-size nodes tensile test conducted at low temperature with Q345 B and Q420 C leg member angle steel which commonly used in 500 kV transmission tower.The effect of punching and drilling at low temperature on failure load and failure mode of bolted joint about different diameter and arrangement was studied.The study found that,in the cold area of-45℃,adopted components should be selected from the material,steel quality grade should use C grade steel,and welding treatment should be treated with caution for high strength steel.When the thickness of steel t is less than or equal to 16,with the four kinds of steel: Q345 B angle steel,Q345 B welded joint,Q420 C angle steel and Q420 C welded joint,the value of strength reduction factor at the low temperature are recommended to be 0.95,0.85,0.90,0.80,respectively.There are some influences on the static bearing capacity of the bolt connection by the hole forming method of the angle steel.If only considering the static bearing capacity at low temperature,it is sufficient to select punching for the processing of nodes about the design requirement.