| Steel structure has been widely used in construction because of its advantages of light weight and high strength.Early beam-column joints were spliced together by welding technology,which led to the joints to be rigid and prone to brittle failure,which caused the overall structure to fail.However,the connection joint of the extended end plate is widely used in steel structures due to its excellent performance,the connection configuration of the extended end plates and high strength bolts makes the joints discontinuous,which leads to the key issue of semi-rigidity that must be studied in the engineering application and design of the joint.The semi-rigid joint itself reflects acertain of flexibility and mechanical nonlinearity.In order to obtain the real joint performance in the structure,the initial rotation stiffness of the joint becomes an indispensable part of the structure design.At present,the methods to obtain the rotational stiffness of the joints are composed of three methods: experimental research,numerical simulation and theoretical calculation.However,in the experiment,due to the beam tip loading method,the research on the performance of the joint under the antisymmetric load state has not been studied in depth,which leads to certain difference in the force performance of the panel zone.In this paper,aiming at the connection joint of the extended end plate,the cyclic loading test on the top side of the column is carried out to study the mechanical characteristics of the joint under antisymmetric load,determine the influence of the shear deformation of the panel zone on the performance of the joint,and give the calculation model of the initial rotational stiffness of the connection joint.The main research contents of this article include:(1)In the experimental study,4 unstiffened extension end plate connection nodes were cyclically loaded on the top side of the column;two methods were used to measure the rotation angle of the nodes and verify each other.The failure mode,bending moment-rotation curve,skeleton curve,ductility,energy dissipation and stiffness of the end plate connection node under cyclic load are evaluated.(2)Three-dimensional non-linear finite element analysis was performed on the 4specimens of the cyclic loading test using Abaqus software,and the correctness of the finite element results was verified by comparison with the test results.(3)Considering the difference in the mechanical behavior of the side column of the center column,the size of the column section,the bolt diameter,the thickness of the end plate,the length of the beam and the section form of the end plate,etc.,the parametric research and analysis of the nodes are carried out.(4)Calculate the stiffness of the flexural component in the component method,introduce the meshless theory to calculate the balance equation of the thin plate bending theory,so as to calculate the deflection and deformation of the plate,use the Galerkin weak form to construct the boundary conditions,and introduce the meshless shape function discrete,the approximate value of the partial differential equation solution for the thin plate bending problem.Fitting the influence coefficients of the bending stiffness of the slab under different boundary conditions,and providing a basis for the calculation of the stiffness of the joint flexural component.(5)Revise the calculation model of initial rotation stiffness according to the force transmission mechanism of the node.The theoretical analysis of the stiffness calculation of each component of the end-plate connection node is carried out,in which the large deflection theory of the thin plate and the mesh-free algorithm are used to fit the influence coefficient of the boundary conditions,so as to improve the calculation method of the stiffness of the flexural component.Meanwhile,when calculating the stiffness of the shear component,consider the limiting effect of the column web stiffener.Tests and finite element results are used to verify the correctness of the theory. |
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