Degradation Law And Evaluation Of Axial Compression Performance Of Locally Corroded X-joints

Tubular joints are widely used in bridge and ocean truss structures considering its simple appearance and excellent bearing capacity.However,the steel structures are prone to corrosion owing to their application scenarios,which seriously threatens the safety performance of steel tubular structures.For steel tubular joints,due to the complex stress distribution in the joint area and the different influence of the change of corrosion location on the degradation of the bearing capacity of the joint,it is no longer applicable to evaluate the degradation of the bearing capacity of the joint only based on the corrosion rate,so it is necessary to study the degradation law of the bearing capacity of local corroded joints.In this paper,the X-joint is taken as the research object,the mechanical performance degradation law of local corroded X-joint under the pressure of brace is summarized,the degradation mechanism of local corroded joint under the pressure is revealed,the evaluation method and design formula are put forward,which has important reference significance for the prediction of local corroded joint bearing capacity degradation.Firstly,the degradation tests of bearing capacity of 2 uncoroded joints,3 overall corroded joints and 4 local corroded joints were carried out.The results show that:(1)corrosion generally does not change the failure mode of the joint,only makes the plastic deformation more obvious in the joint area,or making the corrosion pit near the joint area is prone to deformation or cracking due to stress concentration.(2)With the increase of the corrosion rate,the bearing capacity and the initial stiffness of the joint will be significantly degraded,and the change of the circumferential corrosion position of the main pipe has a great influence on the ultimate bearing capacity of the X-type intersecting joint.The most unfavorable position for the degradation of the circumferential bearing capacity of the main pipe is between the side wall of the main pipe and the joint area.After that,the finite element model is established by ANSYS,and the reliability of the model is verified by experiments and related literature.On the basis of the model,the single parameter and double parameter analysis of X-joint is carried out.The results show that:(1)when the thickness loss rate is the same,the corrosion pit shape has little effect on the bearing capacity of the joint,and the corrosion rate caused by the increase of the depth and diameter of the corrosion pit makes the bearing capacity of the joint drop sharply,while the influence of the corrosion depth on the bearing capacity of the joint is greater than that of the diameter of the corrosion pit.(2)The influence of axial corrosion location on the bearing capacity of the joint is greater than that of circumferential corrosion location.Along the axial direction of the chord,the closer the corrosion is to the joint intersection,the more obvious the degradation of the bearing capacity of the joint is,and it has a certain range.When the distance coefficient k of the axial corrosion position is greater than 2,the influence of corrosion on the degradation of the bearing capacity of the joint can be ignored.(3)The most unfavorable position along the chord along the radius direction changes with the thickness loss rate.When the DOT is not more than 45%,the most unfavorable position is on the chord side wall.When the DOT is more than 45%,it gradually transfers to the middle of the intersection area and the choord side wall.Finally,based on the relevant theoretical model,the test and finite element analysis are carried out to reveal the degradation mechanism of the bearing capacity of the joint.At the same time,the equivalent thickness loss rate is defined as the evaluation index of the degradation of the bearing capacity of the corroded joint through multiple regression,and the bearing capacity design formula of the local corroded X-joint is proposed with five factors and four levels of orthogonal verification.This paper has 68 pictures,34 tables and 84 references.