The Research On The Mechanical Performance Of The Square Concrete Filled Steel Tube With T-stub Connector

Beam-column joints play the role of transferring beam bending moment andshear force.Its performance quality directly affect the structure of the overall reaction.Beam-column joints is the key in the structure design.Now the behaviors of H-sectionsteel column joint have been systemically investigated by the researchers at home andabroad, but the research on CFST semi-rigid joints has just started. The rationaltheoretical analysis model and the calculation method of joints need to be furtherstudied.T stub connector is a new type of beam-column joints connection, which theconnection of T stub connector and square concrete filled steel tubular column usingthe penetrated high-strength bolt，the connection of T stub connector and H-sectionsteel column welded.Based on the traditional research methods of steel-concretecomposite joints, in the dissertation, the performances of the joint have beenextensively investigated by experimental study, finite element simulation andtheoretical analysis. The main achievements in the dissertation are as follows:(1)Based on the wide range of the domestic and foreign literatures, thecomprehensive review and summary have been carried, including the present researchsituations of CFST column, T-stub connector and steel-concrete composite joint. Asystematic classification and study method of semi-rigid connections are analyzed.The models of moment-rotation relationship of joints have been discussed.(2) The pseudo static experiments on the behaviors of six crisscross joints of amoment-resisting frame consisting of CFST column and steel beam have been carriedout. The test parameters varied included the axial load level on the column, the size ofT-stub connector, the scale of penetrated high-strength bolt and different specificationof CFST. To investigate the mechanical behaviors of the composite joints, the failuremodes, hysteretic performance, shear strength, bearing capacity degradation, stiffnessdegradation, energy dissipation and strain were evaluated in detail. To simulate theearthquake action, the antisymmetric loading forms at the ends of beams were adopted.The experimental results indicated that the shear failure modes were arisen, but thenew type joint were provided with higher carrying capacity, bigger initial rotationalstiffness, good ductility and energy dissipation ability, which indicated that the newtype composite joints possess excellent seismic behavior.(3) Taking the test joints as prototypes, on the base of the geometrical nonlinear,material nonlinear and contacting nonlinear of component of joints, the entity modeling and fine meshing of joint have been developed using the finite elementsoftware ABAQUS, which can reasonably simulate the experimental boundaryconditions, loading modes and select solver, so the entire loading process of finiteelement analysis has been conducted. The results of ABAQUS are in conformity withthe tests. The axial pressure ratio of CFST columns, the preload of high strengthbolts,which how to influence the mechanical performance of composite joints, havebeen evaluated. Through the finite method analysis, lots of details can be got, whichwere indiscoverable in tests, such as: the stress condition at panel zone concrete, thecontact stress distribution at T-stub flanges.(4) Founded on the analysis on force transmission mechanism of cri sscross joint,the possible failure modes can be made. On this basis, the various components of thecontrast node as determined by the maximum flexural capacity of composite beamsthe maximum flexural capacity, derived node flexural capacity is calculated; Based onthe three broken lines calculation model of shear resistance in panel zone webs ofinner and outer steel tubes, the calculation model of moment resistance in panel zoneflanges of inner and outer steel tubes and the calculation model of diagonalcompression bar in panel zone concrete, the shear capacities of the joints have beenestablished using the superposition principle.The research results show that: the proposed bolted T-stub compositeconnections exhibit good mechanical performances, meeting the design requirementsof current codes for seismic resistant frames or frame-core wall structures.