Study On The Bearing Performance Of Q420 Equal Angle Steel Subjected To Local Corrosion

Steel structure tower is important structure form of transmission lines in our country,in recent years,with the development of the industry and economy,the intensity of transmission and transmission distance increased,material put forward higher requirements for iron tower.Due to the low cost,convenient installation and high bearing capacity,Q420 equal angle steel gets more and more widely used in power transmission tower.However,due to long-term exposure to harsh external environment,angle steel members in transmission towers are vulnerable to corrosion,which results in the deterioration of the bearing capacity of members and poses a serious threat to the service life of transmission towers.Compared with uniform corrosion,local corrosion has the characteristics of concentrated corrosion area,rapid development,large corrosion depth and strong concealment.It is easy to produce stress concentration effect,so that the component is more likely to suddenly occur brittle fracture without obvious deformation symptoms,resulting in serious safety accidents and economic losses.Therefore,it is of great practical significance to study the deterioration of bearing performance of angle steel members by local corrosion.Based on corrosion test data,this paper adopts the method of numerical simulation,the effects of local corrosion surface density(DOL),pit depth,corrosion range,corrosion position and slenderness ratio of members on the bearing performance of equal angle steel members with tow different sections(width to thickness ratio over-limit and non-over-limit)were studied under axial loading.The influence law of local corrosion on the ultimate bearing capacity and failure mode of Q420 equal angle steel members was expounded.The formulas for evaluating the ultimate tensile and compressive bearing capacities of locally corroded angle steel members were presented.This paper has mainly completed the following aspects:(1)Respectively established the finite element models of axial tension and axial compression angle steels with local corrosion.The influences of element type,initial defect,constraint mode,pit-shape and mesh size on the calculation results of ultimate bearing capacity of equal angle steel members were discussed.And the accuracy of the finite element model was verified with the experimental data.(2)The locally corroded angle steel under axial tension and the axial compression is taken as the research object,680 locally corroded angle steel finite element models were calculated and analyzed.The influence of various parameters on the axial mechanical properties of two kinds of angle steel members with different sections(width to thickness ratio over-limit and non-over-limit sections)was studied.The deterioration law of the ultimate tensile and compressive bearing capacity of the component under the influence of various parameters,as well as the stress distribution and deformation characteristics of the component in each stage were expounded.The results show that the ultimate tensile capacity of locally corroded angle steel members is mainly affected by DOL and pit depth,while the ultimate compressive capacity is mainly affected by DOL,pit depth and corrosion range.For tensile members,the difference of bearing capacity deterioration caused by single and double limb corrosion should be taken into account,while for compression angle steel members,the difference of bearing capacity deterioration between the over-limit and non-over-limit angle steel is obvious.(3)The section damage coefficient is used as a parameter to comprehensively consider the influence of DOL and the depth of corrosion pit,and the reduction formula of the ultimate bearing capacity of locally corroded angle steel is fitted by nonlinear regression method.For axial compression angle steel members,the influence of corrosion range is also considered.The fitting formula is compared with thickness reduction method,stiffness reduction method and damage volume method.The results show that the formula of section damage method presented in this paper has high accuracy and can be used to evaluate and calculate the ultimate bearing capacity of locally corroded angle steel in practical engineering.