Analysis And Experimental Study On Mechanical Properties Degradation Of Corroded High Strength Bolt Joints

In bridge engineering,corrosion is one of the important reasons that threaten the safety of steel structure bridges.Frictional high-strength bolted connections are a main form of connection for steel structure bridges.The impact of corrosion on its mechanical performance is related to the safety of steel structure bridges.The paper studies the degradation law of the bolt pretightening and the friction coefficient of the contact surface corroding high-strength bolt connection nodes,and the variation law of characteristic load.A static mechanical test was conducted on the corroded high-strength bolt joints to explore the effect of corrosion on the shear resistance of the high-strength bolt joints.First,prepare one-sided two-bolt high-strength bolt connection specimens and perform electrochemical corrosion,and then perform tensile test and analysis on the corroded specimens to observe the failure mode and corrosion form of the one-sided two-bolt bolt connection nodes;The change trend of the load-displacement curve of the connection node;again,a test method for the preload and slip coefficient of the corrosion specimen is proposed to study the degradation law of the friction coefficient and preload;finally,the corrosion resistance to friction and shear is studied The influence law of bearing capacity and ultimate bearing capacity is analyzed,and the tensile plasticity of the connection node of two bolts on one side is analyzed.Besides,on the basis of the above experiments,the finite element analysis method was used to explore the effect of corrosion on the mechanical performance degradation of high-strength bolt connections.Firstly,the finite element analysis of the two-side bolt connection is carried out to verify and supplement the experimental results,combined with the conclusion of the tensile experiment to summarize the change law of the bearing capacity of the high-strength bolt joint after corrosion;Based on the results of the numerical simulation,the finite element simulation method was used to extend the analysis of the change of the mechanical properties of the high-strength bolt group under different corrosion rates.Finally,based on the bolt group finite element simulation results,the Dalian Xinghai Bay Bridge truss beam was used as the engineering background to establish The calculation model of steel truss predicts the influence of the corrosion of bolt joints on the mechanical performance of steel truss.Through the test and numerical analysis,it was found that the corrosion of the test piece was uneven after the test piece was corroded.All the tensile fracture of the test piece occurred at the position of the bolt hole of the main tensile plate.In the middle,due to the relative movement of the plate and the bolt rod,two slips occurred.The load-displacement curves of all specimens can be divided into five stages:(?)friction transmission stage,(?)slip stage,(?)bolt and rod force transmission stage,(?)hardening stage and(?)failure stage;The preload force and slip coefficient of the corrosion test piece decrease with the increase of the corrosion rate;corrosion has no significant effect on the ultimate slip rate and initial slip rate of the connection piece,but as the mass loss of the test piece increases,its energy Absorptive capacity decreases logarithmically;frictional shear capacity(initial slip load),full slip load,yield load and ultimate load all decrease as the corrosion rate of the bolt and the entire specimen increases;one-sided finite element simulation corrosion There are four stages in the load-displacement curve of the two-bolt model,namely(I)friction stage,(II)slip stage,(?)elastic stage and(?)yield stage.There were two obvious slips in the second stage;due to the limitations of the experiment and the finite element simulation,the results of the finite element simulation and the tensile test have errors,but they have little effect on the research results;the characteristic load obtained by the finite element simulation Comparable with the characteristic load obtained by the tensile test;the result of the finite element analysis of the bolt group found that the load-displacement curve of the friction type high-strength bolt group with a large number of bolts has no obvious displacement mutation section compared with the one-sided two-bolt model.The displacement curve is relatively stable;after the corrosion of the friction type high-strength bolt group,as the corrosion rate increases,each characteristic load decreases significantly;the higher the corrosion rate of the steel truss under the same load,the greater the maximum bending moment and shear value.The research results of this paper are intended to provide a theoretical basis for the safety assessment of the bolted joints of the bridge after corrosion,and to provide a research basis for the importance of rust prevention of steel bridges.