Mechanical Behavior Of Connection For Concrete-filled Double Steel Tube Column To Steel Beam With Ring Plate Of Top-flange-welded And Bottom-flange-bolted

Compared with traditional steel pipe concrete columns,concrete-filled double steel tube column has higher bearing capacity,greater flexural stiffness,lighter self-weight and higher space utilization,and are simple to construct and suitable for assembly-type production.The seismic behavior of the beam-column connection in the framing system is crucial to the security It has been shown that the beam-column connection,which combines the advantages of concrete-filled double steel tube column,has good ductility,high energy dissipation capacity and high node stiffness,and the seismic behavior meets the connection requirements.However,due to the existence of double-layered steel pipes inside and outside,the nodal connection form between column and beam is restricted,which hinders the engineering application and promotion of concrete-filled double steel tube column structure.In this paper,we propose a kind of connection for concrete-filled double steel tube column to steel beam with ring plate of top-flange-welded and bottom-flange-bolted,and carry out the seismic behavior experimental research and theoretical analysis,the main research work and the results achieved include the following four parts:1.Three connections for concrete-filled double steel tube column to steel beam with ring plate of top-flange-welded and bottom-flange-bolted were designed,with a constant axial force applied to the top of the column and a horizontal low circumferential reciprocating load applied to the end of the column,and the width of the outer ring plate and the extension length of the upper ring plate were taken as the research parameters for the test.It was found that the beam end damage occurred in all three specimens,and the damage patterns mainly included warpage deformation of the upper flange of the steel beam,pulling apart of the weld joint between the upper ring plate and the steel beam,slip deformation of the lower ring plate and the flange of the steel beam,and slip deformation of the connection plate of the steel beam web.Increasing the width of the ring plate improves the connection stiffness,which makes the upper flange of the steel beam warp more significantly;decreasing the upper ring plate outreach length makes the plastic hinge position closer to the column wall,which increases the beam end bending moment and makes the upper flange weld pull apart prematurely.2.According to the hysteresis curve of the specimen obtained from the test,the hysteresis behavior of the connection under the low circumferential reciprocal load is analyzed,and the skeleton curve of the specimen is extracted from the hysteresis curve.The connection strength and stiffness degradation,ductility,energy dissipation capacity and deformation of important parts were analyzed.The results show that increasing the width of the ring plate can improve the bearing capacity of the specimen and the connection stiffness,and reducing the extension length of the upper ring plate has less effect on the bearing capacity of the specimen,but will reduce the ductility of the specimen;overall,the connection specimen has good energy dissipation and meets the ductility requirements.3.In order to make the skeleton curve more regular,the dimensionless treatment was carried out to reduce the differences caused by the parameters of connection for concrete-filled double steel tube column to steel beam with ring plate of top-flange-welded and bottom-flange-bolted.The hysteretic restoring force model of the connection is established based on the hysteresis rule of the connection.The theoretical model is compared with the test results and the results show that the theoretical model is in good agreement with the test results,and the restoring force model established in this paper can reflect the hysteresis characteristics of this type of combined connection more accurately,which can provide theoretical reference for its engineering design and seismic response analysis.4.The shear bearing capacity is mainly provided by six parts:square steel tube web and flange,anchored web,round steel tube web,upper and lower ring plate and concrete in the core area.And the theoretical value was compared with the test value and the error analysis was carried out.The results show that the shear bearing capacity calculated by the method of this paper is close to the test results and is on the safe side,and the shear bearing capacity calculation method of this paper can provide reference for the actual engineering design.