Loss Of Clamping Force Of Bolts In A Corrosive Environment And Its Effect On The Bearing Capacity Of Steel Structure Joints

For steel structure,corrosion is one of the most serious problems,especially for the widely used friction type high-strength bolts.As the corrosion damage of bolts will affect the safety and durability of high-strength bolt friction type connection,it is necessary to establish effective monitoring methods and safety evaluation standards for bolts prone to corrosion.However,for a long time,people have neglected the influence of local corrosion of high-strength bolts on structural damage and performance evolution.There are relatively few studies on the accurate and effective monitoring technology of high-strength bolt corrosion degree,and even fewer studies on the quantitative relationship between the corrosion degree of high-strength bolts,the safety of high-strength bolts and the degradation of bearing capacity of high-strength bolt connections.Friction type connection with highstrength bolts is one of the important joint connection forms of steel structure.If the loss of clamping force of high-strength bolts and the change rule of bearing capacity of friction type connection with high-strength bolts under corrosive environment can be quantitatively analyzed,and the potential danger can be revealed,then the accurate safety appraisal can be made for the steel structure joints that need to be repaired and strengthened in time.In this paper,taking the steel structure high-strength bolt and high-strength bolt friction joint as the research object,the research on the loss of high-strength bolt’s clamping force and its influence on the bearing capacity of steel structure joint under corrosive environment is carried out.The research contents include the following aspects:1.To verify the reliability of the method of using fiber grating sensor to monitor the change of bolt clamping force.Through the tensile test of high-strength bolt and the finite element simulation of strain transfer between fiber and bolt,the result shows that the method of using fiber grating sensor to monitor bolt clamping force is very reliable.2.Through the finite element simulation analysis of the corrosion of single bolt head,the law of the loss of clamping force of high-strength bolt with different initial preload under the corrosion environment is obtained.The simulation of high-strength bolt corrosion mainly focuses on the two directions of bolt head corrosion along its thickness direction and along its radial direction.Then according to the stress of bolt rod in different corrosion stages,the loss degree of bolt clamping force is known.3.Through the simulated accelerated test of single bolt head corrosion and the use of fiber Bragg grating sensor to monitor the change of bolt clamping force,the law of bolt clamping force loss under corrosion environment is obtained.The experimental results of the loss rule of the clamping force of the high strength bolt under the corrosive environment are compared with the simulation results,and the experimental results are basically consistent with the simulation results of the finite element method.4.Through the finite element numerical simulation,the shear connectors of highstrength bolts with different degrees of corrosion on the bolt head are analyzed,and the influence of different degrees of local corrosion on the bearing capacity of friction type connection of high-strength bolts is obtained.