Finite Element Analysis On Mechanical Behavior Of Circular Concrete-filled Double Skin Steel Tubular Column To Steel Beam Joint

Concrete-Filled Double Skin Steel Tubes Structure,(CFDST) as a new type of concretefilled steel tubular composite structures, has received many scholars’ attention. CFDST hasadvantages of greater flexural bearing capacity, light weight and good fireproof performancebesides the traditional advantages. Despite the history of study on CFDST at home and abroadis just about20years so far, CFDST has been applied in some practical engineering and goodeffects obtained. At present, achievements on CFDST joints research are not much. However,as the key part of the overall structure, especially in frame structures, the joint play a vital roleto the integrity and stability of the structure when the structure is on the elastic-plastic stageafter suffering from severe earthquakes. In this paper, under low cycle load, mechanicalproperties of CFDST beam-column joints in frame structures was studied through numericalsimulation, the main contents and results are as follows:（1）Nonlinear refined finite element model of CFDST beam-column joints (the middleof the frame columns) under reverse cyclic loading was established. Using the finite elementsoftware ABAQUS to model and mesh joints, and the boundary conditions and loadingmethod were reasonably set. Material nonlinearity, contact nonlinearity and geometricnonlinearity were considered in the model, and the interact between internal and external steeltube and the concrete between them was also taken into account. Besides, back-stresses, thebauschinger effect of steel, tension and compression damage factor of concrete sandwich werealso taken into consideration.（2）Numerical simulation analysis on specimen of CFDST beam-column joints underantisymmetric reverse cyclic loading at the end of the beams was conducted. Six mechanicalperformance indexes which were the load-displacement hysteresis curve, theload-displacement skeleton curve, ductility, strength degradation and stiffness degradation andenergy dissipation capacity of the end of beam applied load were discussed in this paper.Combined with the analysis of the results of previous test, it shows that the finite elementmodeling method is reasonable and reliable. Through the numerical simulation, the failureprocess of a typical joint were analyzed, the results show that the destruction of specimencaused by the plastic hinge of the beam-end joint domain conforms to the "strong columnweak beam" principle in project; when the displacement of the beam end over the limit displacement and continue to increase, column-end joint domain can still assume a certainload with the increasing displacement, which show its good ductility.（3）Based on the above modeling method, the influence of parameters on the mechanicalproperties of the joint by numerical simulation is analyzed, such as the axial compression ratio,the hollow ratio, both inside and outside diameter-thick ratio, different materials strengthlevels, actual steel ratio of column section, confinement effect of external steel tube tolaminated concrete, line stiffness ratio of beam-column and so on.