Study On Corrosion Resistance And Mechanical Properties Of Weathering Steel High Strength Bolts

High-strength bolt connection is one of the main connection modes of steel structure,and the joint is the key part of the steel structure.In order to ensure the safety of steel structure,it is necessary to ensure the reliability of the joints.After corrosion occurs,the strength of steel structure components and joints will be weakened,and even affect the safety of the structure.Weathering steel changes the corrosion resistance of steel by adding alloying elements in carbon steel.These alloying elements can make the rust layer generated after corrosion of steel more dense,so as to form a protective effect on the internal uncorroded steel and reduce the corrosion rate.Obviously,it is of great significance to popularize the use of weathering steel to improve the safety and durability of steel structures.At present,there are still many deficiencies in the application research of weathering steel structure,therefore in this paper,the weathering steel corrosion resistance and mechanical properties of weathering steel high-strength bolts.High strength bolts to Chinese standard and American standard as the research object,with a magnitude of 10.9 ordinary high strength bolts by contrast,has carried out the model test and numerical simulation,the main research contents and conclusions are as follows:1)high strength bolts and Q420 steel,were assembled into one single bolt double shear plane high strength bolt connection.Considering the difference of bolt type and bolt diameter and pretension,9 groups of test model was designed,each group contains three specimens,one of the specimens without corrosion,the other two specimens respectively for 60 days and120 days of acetic acid salt fog corrosion,The uniaxial tensile test of control model specimens was carried out(note: bolt sheared).2)The shear capacity of uncorroded bolts was compared and analyzed.The results show that the ultimate load of M20 Chinese standard weathering steel high strength bolts was slightly higher than that of American weathering steel high strength bolts and ordinary high strength bolts.The ultimate load of M22 high strength bolts of American standard weathering steel was slightly higher than that of Chinese standard bolts.3)The surface corrosion characteristics,weight loss rate and ultimate bearing capacity of corrosion specimens were compared and analyzed.It is found that with the increase of corrosion time,the rust layer became darker and the bubble thickens greatly.After 60 days of corrosion,the weight loss rate of weathering steel high-strength bolts were higher than that of ordinary high strength bolts,and the American standard bolts were the most;After 120 days of corrosion,the difference of weight loss rate of three kinds of high-strength bolts decreased obviously,and there was little difference between them.Especially in the last 60 days,the corrosion rate of high strength bolts of weathering steel decreased greatly,while the corrosion rate of ordinary high strength bolts was almost unchanged.Due to the formation of partial shielding and protection on the surface of the specimens after the assembly of the specimen,mainly the outer part of the specimen steel plate and the ends of the bolts and other parts which were in contact with the outside world are corroded,while the bolt hole and bolt rod were shielded,corrosion was not serious,so compared with the non-corroded specimens,the bearing capacity of the specimens after corrosion is not significantly reduced.4)In order to study the bearing capacity change of the connecting parts after being completely corroded,the unassembled bolts were exposed to the salt spray test box for 60 and120 days,and then the corroded bolts were assembled into high-strength bolt connectors after rust layer removal,and the unidirectional static tensile test was carried out.It is found that the weight loss rate of the fully corroded specimens was significantly higher than that of the assembled specimens,and the corrosion degree increases significantly,and the difference of different kinds of bolts was more obvious.At the initial stage of corrosion,the weight loss rate of ordinary high-strength bolts is lower than that of weathering steel high-strength bolts,but with the increase of time,the corrosion rate of weathering steel high-strength bolts decreases and the weight loss rate was gradually lower than that of ordinary high-strength bolts,which is the same as the change rule of the weight loss rate of the corrosion of complete specimens.The decreasing degree of bearing capacity increases with the increase of weight loss rate,and the decreasing proportion was close.There was no change in the failure mode at the edge of the bolt fracture surface,indicating that the corrosion pit has little influence on the shear capacity of the high-strength bolts.5)According to the bolt test results and the material property test of the connecting steel plate,the double broken line constitutive model of the steel plate and bolt material was established.Further considering the contact boundary relationship between the connecting parts,the finite element model of the specimen was established and the numerical simulation analysis was carried out.The comparison shows that the simulated load-displacement curve is similar to the experimental results,and the ultimate load and deformation are basically the same,which verifies the accuracy of the numerical model.The results show that the ultimate bearing capacity of corroded specimens is inversely proportional to the weight loss rate,and the reduction ratio is almost linear with the weight loss rate.Bolt pretension and test fixture have significant influence on connection slip,but have little influence on ultimate bearing capacity of bearing type high strength bolt.