Research On Evaluation Method Of Residual Clamping Force Of High Strength Bolt After Corrosion

Corrosion is considered to be one of the main factors affecting the structural degradation and collapse of steel Bridges.Compared with other parts of steel bridge,high-strength bolts are more prone to corrosion.There are a lot of corrosion marks around high-strength bolt joints of steel structure,which will affect the clamping force of high-strength bolts and thus reduce the bearing capacity of high-strength bolts.The corrosion of bolts becomes the main reason of joint slip,which brings great hidden danger to the normal use of steel bridge,and seriously affects the service performance,operation and service quality of the structure.In this paper,the influence of corrosion on residual clamping force of high strength bolt is studied from two directions of thinning along nut thickness and thinning along nut height.Based on the engineering background of Shengli Yellow River Bridge,this paper carried out an experimental study on the evaluation of residual clamping force of corroded high-strength bolts,and drew the following conclusions:(1)Experimental study on high-strength bolt force sensor and axial force calibration.The highest accuracy is achieved when the strain gauge is placed 25 mm inside the bolt;There is a linear positive correlation between the axial force and the strain value of the high-strength bolt when the bolt is stressed within the design value of bearing capacity.(2)Numerical analysis of the influence of nut corrosion shape and size on the axial force of high bolts.The loss of clamping force increases with the increase of the damage degree of nut section.With the same degree of cross-section damage,the clamping force loss rate of high-strength bolt is relatively slow in the early stage,but increases in the middle and late stages of cutting.Under the same cutting mode,M16high-strength bolt reaches the maximum clamping force loss rate at the fastest time.Under the same corrosion depth,the clamping force loss degree of corrosion along the nut thickness is greater than that along the nut height,and the clamping force loss degree of simulated trapezoidal corrosion and funnel corrosion is smaller than that of cutting along the nut thickness.The regression equation for evaluating the clamping force loss ratio of high strength bolts under different specifications and cutting methods is established.(3)Experimental study on residual axial force of rusty nut and high bolt and verification of evaluation model.According to the finite element analysis and test results,the variation trend and law of the finite element simulation results and the test results are basically the same,which verifies the applicability and effectiveness of using finite element numerical simulation method to analyze the simulation corrosion test of high strength bolts.