Experimental Study On The Mechanical Behavior Of T-Stubs With Q690 High Strength Steel And 12.9 High Strength Bolts

The diversification of architectural forms has led to the development of new highefficiency,energy-saving and environmentally friendly high-strength steel products.High-strength steel has been used in domestic and foreign engineering projects.The assembling and high strengthening trend of steel structures has made steel structure nodes more complicated and higher requirements on connection performance.And there is currently not mature for high-strength steel joints in domestic specifications.In order to understand the mechanical behavior of high strength steel bolted connections,promote the application of high-strength steel,the experimental study on tensile behavior of welded T-Stubs with Q690 D high strength steel and grade 12.9s high strength bolts is presented.At the same time,the Q345 B strength steel and grade 10.9s high strength bolts have also been selected to clarify the impact of steel and bolt strength levels on the mechanical behavior.The main research work and achievements of this paper are :(1)The article introduces the provisions on the tensile connection of high-strength bolts in steel structure design codes of different countries from construction requirements,pretension and design method of flange thickness.(2)The material test of Q690 D steel,Q345 B steel,grade 10.9s and 12.9s high strength bolt with large hexagon head was conducted.A test on the torque coefficient of four type high strength bolts was conducted by batch.The static test of the 28 highstrength bolted connections was completed,and the load-displacement curve was obtained.(3)In this test,the test data of each group of test pieces were compared.the influence rules of The steel strength grade,steel welding process,bolts strength grade,bolts diameter,marginal coefficient and bolts pretension on mechanical properties of the T-stubs were obtained.the applicability of the normative formula on high-strength steel was also studied,and the difference between the standard calculation results and the test results was discussed.(4)Compared with the experimental and finite element analysis results,the reliability of the finite element model is verified,and the parametric analysis is carried out by the validated finite element model.The influence of various parameters on the initial stiffness and plastic bearing capacity of T-stubs is investigated.The finite element analysis of T-stubs with different thicknesses was carried out.The difference between the fitting results and the EC3 calculation results was compared.The applicability of the EC3 calculation formulas for T-stubs of high-strength steel or ordinary steel and the accuracy of the standard for the prediction of failure modes were discussed.The innovation of this paper:(1)In addition to the usual influencing factors,the test considers the influence of the welding process of Q690 D high-strength steel on the mechanical properties of TStubs;(2)A test on the torque coefficient of four type high strength bolts was conducted.The paper calculates the torque value of the bolt by the torque coefficient.The pretension was applied to 12.9 high strength bolts with the torque value,and the influence of pretension on bolted connections was studied;(3)The influence of the marginal coefficient on the mechanical properties of the TStubs with Q690 D high strength steel and grade 12.9s high strength bolts is compared by the three cases,that is,the length of the flange plate is constant,the distance from the center of the bolt hole to the weld toe is constant or the distance from the center of the bolt hole to the end of the flange is unchanged.