Study On Seismic Behavior Of Steel Frame Beam Column Joints With Steel-cast Elements

The joint connected by steel castings is a kind of semi-rigid joint,and its chamfer can avoid the stress concentration caused by welding.The traditional steel joint will produce large residual deformation under earthquake,which leads to irrecoverable damage of the structure and brings great difficulties for post earthquake maintenance.The self reset structure system can effectively control the residual deformation of the structure,so that the structure can quickly restore its function without or a small part of maintenance after the earthquake.In order to solve the defects of traditional steel casting connection joints,based on the characteristics of self reset structure,this paper proposes a steel casting connection of self reset steel frame beam column joint.The beams and columns of this kind of joints are bolted by steel castings,and prestressed steel strands are arranged along the inner side of the beam flange.After prestressing the steel strand,the beam column is compressed,and the beam column connection has the bending stiffness to meet the normal use of the structure.The mechanical mechanism,failure mode,seismic performance and self reset ability of the self reset beam column joints with steel castings are studied by using the finite element software ABAQUS and theoretical analysis,and the design method of the joints is proposed.The main contents of this paper are as follows:(1)By observing the stress distribution of the self reset joint of steel casting connection,the stress deformation and failure mode are analyzed.Under the action of beam end load,the steel castings yield and consume energy,and the prestressed steel strand ensures the self reset performance.During the loading process,the beam,column and steel strand remain elastic,and the joints can be restored to the non-destructive state only by replacing the steel castings after the earthquake.There are two modes of joint failure: the yield belt through horizontal leg and rib stiffener or the yield belt through vertical leg and rib stiffener.(2)The influence of different parameters on the bearing capacity of the self reset joint of steel casting connection under static load is analyzed.The results show that the initial prestress of steel strand has the greatest influence on the bearing capacity of the joint,followed by the thickness of the vertical leg of steel casting,and the thickness of the horizontal leg and rib stiffener of steel casting has relatively little influence on the bearing capacity of the joint.(3)From the aspects of bearing capacity and self reset capacity,the mechanical performance of the self reset joint of steel castings with the same parameters and the joint of traditional steel castings under the action of low cycle cyclic load is comprehensively compared and analyzed.The results show that the traditional steel casting connection has low bearing capacity and large residual displacement after unloading,while the steel casting connection has high bearing capacity and good self reset performance.(4)The seismic behavior and self reset ability of the self reset joints with different parameters under cyclic loading were studied.The results show that the hysteretic curves of each node are typical "double flag type",with good self reset performance and energy dissipation capacity.The bearing capacity and energy dissipation capacity of the joint can be improved by increasing the thickness of the vertical leg,horizontal leg and rib stiffener.Increasing the initial prestressing force,decreasing the length of strand or increasing the number of strand can improve the bearing capacity and self reset performance of joints,but the energy dissipation capacity is weakened.(5)Combined with the results of numerical simulation,the mechanical performance of the joint is analyzed theoretically,and the joint design method is proposed.Suggestions for the application of steel castings connected self reset steel frame beam column joints in practical engineering are given: the thickness of vertical and horizontal legs of steel castings is 1.2～1.6 times of the web thickness of steel beam,1～1.6 times of the web thickness of steel beam,the diameter of 1×7 steel strand is 15.2mm,the initial prestress is 60～120k N,and the length should not be less than 2000 mm.