Study On Flexural Hysteretic Behavior Of T-shaped Curved Round Steel Tube Joints And Their Curved End Plates

T-shaped bending round steel tube joint is formed by welding the main pipe at an Angle on the basis of T-shaped circular steel tube joint.The curved end plate reinforced node is a new type of joint made of T-shaped bending round steel tube joint as the basic component.By changing the form of direct welding of the branch pipe,the joint is welded with the curved end plate first and then connected with the main pipe by high strength bolts.In this paper,experimental,finite element and theoretical analyses are used to study the flexural hysteretic properties of T-shaped curved circular steel tube joints and curved end-plate reinforced joints.The formulas for calculating the flexural capacity of these new joints and the theoretical models of bending moment-angle are put forward.The shrinkage test of bending hysteresic properties of T-shaped bending round steel tube joints and curved end-plate reinforced joints with different main connection angles A and different branch pipe thicknesses t₁ was carried out.The failure mode and hysteretic properties of T-shaped curved round steel tube joints and their curved end-plate reinforced joints were investigated.The test results show that:（1）The test results of T-shaped bending round steel pipe joints show that the main failure is the pipe wall cracking in the main near weld zone,the main joint weld cracking and the buckling on both sides of the main near weld,and the bearing capacity is mainly affected by the main pipe wall cracking and the main joint weld cracking.（2）With the decrease of the thickness of the branch pipe,the properties of the T-shaped bending round steel pipe joints change obviously.To some extent,the thicker the branch pipe is,the better the properties are.The main connection Angle has little influence on the flexural performance of the joint.（3）The test results of the reinforced nodes of the curved end plates show that the main damage is the cracking of the near weld zone of the curved end plates and the buckling failure of the curved end plates,which protects the main pipe from damage and significantly improves the bearing capacity,realizing the"strong node,weak member",protecting the safety of the nodes,and having the advantage of replaceable after damage.ABAQUS finite element program was used to verify the T-shaped curved round steel pipe joints and their curved end-plate reinforced joints.A finite element model of T-shaped curved round steel tube joint and its curved end-plate reinforced joint is established considering geometric nonlinearity material nonlinearity and contact problems.The accuracy of finite element modeling is verified by comparing with experimental resuils.On this basis,the end plate with surface strengthening node BASE model is set up to full scale size change analysis,and the head diameter thanβ,director of the diameter and the thickness of head thanγ,director of A and surface thickness of the endplate t_sep connection Angle parameter analysis,the factors which influence the results show that the raiseβor reduceγcan significantly improve the surface end plate reinforcement node of the bending hysteresis performance;When the main connection Angle varies from 0°to 7.5°,it has little effect on the bending hysteresia performance of the curved end-plate reinforced joints.When the thickness of the curved end plate t_sep is in the range of 8mm-12mm,the flexural hysteretic performance can be significantly improved.Based on the test and finite element analysis,the ultimate flexural capacity formula and the theoretical model of bending moment-angle of the curved end plate reinforced joints are proposed.The applicability and accuracy of the ultimate flexural capacity theory and the moment-angle theoretical model proposed in this section are verified by comparing with the experimental results,the finite element verification results and the variparametric results of the finite element.The influence of each parameter on ultimate flexural capacity and moment-angle curve is discussed.