Research On Wind Resistance Design Of Extra-high Voltage Steel Tubular Tower Based On Multiscale Analysis

During to the uneven distribution of resources in China,with more in western and northern,less in eastern and sourthern.In order to make full use of resources,the state has vigorously developed extra-high voltage transmission technology.As an important part of overhead transmission lines,extra-high voltage transmission tower plays an important role in safety and reliability.Extra-high voltage transmission tower is a flexible system,which is greatly affected by wind load.Steel tube tower is widely used in extra-high voltage transmission line because of its isotropic forces.Therefore,ANSYS numerical simulation method is used in this paper to study the wind resistance design of extra-high voltage steel tube tower.Conventional modeling methods are divided into two kinds: one is based on beam element,bar element and beam-bar element,the other is entity element model.The stress distribution of each node couldn't be seen in the former method,and too much calculation was required in the latter.Therefore,multi-scale method is used in this paper to build the model,which is to find out the dangerous parts on the single-scale model of beam element modeling.After removing this part,the solid element model is built here.Because of the difference degrees of freedom between beam element and solid element,MPC184 element was used to connect the two elements.The established multi-scale model was used to check the stress situation at the fine points,meanwhile,the computational load of the computer was reduced with this method.Pulsating wind was generated by AR method and superimposed with average wind.Then the pulsating wind was acted on the single scale tower-line system model of beam element,the result showed that the most disadvantageous wind direction was 90 degree.By comparing the single tower model of beam element,the tower-line system model of beam element and the multi-scale tower-line system model,the result showed that the multi-scale tower-line system model was more in conformity with the actual stress situation,Especially the calculation of stress and bending moment.90 degree wind load was acted on the multi-scale tower-line system model until destroying.The result showed that the first yield failure occured at the joints of the tower body.From the stress nephogram,the plastic zone was accused by the uneven distribution of stress outside the joints.Stress concentration occured at the intersection of the inner main pipe and the upper branch pipe parallel to the wind direction and the lower branch pipe perpendicular to the wind direction.Then,the destroyed parts were strengthened and designed.As the destroyed location was KK type intersecting joint,this paper adopted two methods to design,one was changing its own parameters,the diameter ratio beta of branch pipe to main pipe,the diameter-thickness ratio gamma of main pipe,the thickness ratio_of branch pipe tomain pipe;the other was changing the structure and add diaphragms and supporting rods at the joint.Through comparation of several methods,it can be concluded that in actual wind-resistant design of extra-high voltage steel tube towers,the bigger the diameter ratio is,the better the value range is which floating from 0.2 to 0.45;the smaller the diameter-thickness ratio of the main pipe is,the better the value range is which best value range floating 20 to 60.If the wall thickness of the main pipe is kept unchanged and the diameter of the main pipe is increased appropriately,the bearing capacity of the main pipe will be increased slightly;The change of wall thickness ratio has the least influence on the bearing capacity of the joints,and basically remains unchanged;The method of adding supporting rods is better than that of adding diaphragms.The degree of bearing capacity improvement of joints not only depends on their own bearing capacity,but also on the bearing capacity of the connecting rods.Generally speaking,the method of changing its parameters is better than the method of changing its structure.The most advantageous scheme is reducing the diameter-thickness ratio of the main pipe,that is,keeping the main pipe unchanged and increasing the thickness of the main pipe.This is of great significance for wind-resistance design in the future.