| The Concrete-Filled Steel Tubular structure (CFST) is a constructional element formed by pouring concrete in an empty steel tube, and then, making them form the whole and work together. The Concrete-Filled Steel Tubular Structure brings into full play the compressive property of concrete and the tensile property of steel, and combines them into a good interaction effect. The constraint applied by steel tube makes the concrete from the state of single way force into a spatial forcing system, which enhances the compressive strength and the deformability. The Concrete-Filled Steel Tubular Structure is a combination of high bearing capacity, good plasticity and toughness, ease of application, refractory performance and good economic returns. Thus, the Concrete-Filled Steel Tubular Structure is a structural form with a good development prospect.At present, the critical factor which limits the application and dissemination of CFST structures is their joint connection form Joints are force transfer hubs of the frame structure, thus they must be not only safe and reliable,to make sure the bending moment,shear and axial force of the beam end can be transferred safely with the combined action of vertical and horizontal loads,but also with a simple connection and ease of manufacture and site operation.Hence, promoting a deep research aimed at the joint of CFST and steel beam, probing the reasonable and effective joint connection scheme,is of great important in theoretical significance and application value.Yet,at present the researches are mainly aimed at the joint of square and rectangle steel tube,and the researches at the CFST with special-shaped section are quite less.To understand the seismic behaviors of T-shaped concrete filled steel tubular column-steel beam joints, four joints with exterior strengthening ring with the reduced-scale of1:2, were designed and manufactured. Among them, EJ-1, EJ-2, and EJ-3were designed according to the design principle of strong column and weak beam and EJ-4according to the design principle of strong beam and weak column. The pseudo-static testing was carried out in civil engineering test center of Yangtze University. The influence on the seismic behavior indices of the column axial compression ratio and the line stiffness ratio of beam to column were discussed. The failure characters, hysteresis curves, skeleton curves, ductility, rigidity degradation and energy dissipation capacity, etc. were studied.The test result shows that the failure mode of strong column and weak beam was local buckling at the end of steel beam flange in the place of variable cross-section, the plastic hinge was occurred, the concrete filled steel tube column and the core area of joint were not damaged. The failure mode of strong beam and weak column was that the steel tube wall of the CFST column under the lower stiffening ring were buckled and cracked, the core concrete were crushed and the plastic hinge was occurred. The maximum shear deformation angle of each joint is of1.44-2.29%of beam-column limit intersection angle, and shear deformation is of not the main factor in structure deformation. With the increase of the axial compression ratio, the shear bearing capacity of the joint increases, but its ductility performance reduces. With the increase of stiffness ratio beam-column line, the shear bearing capacity of the joint also increases and the initial stiffness increases obviously. the displacement ductility coefficient of joints were between3.39and3.91, and viscous damping coefficient of joints were between0.46and0.51, which both complied with code for seismic design of building regulations, it showed that these joints achieved the seismic design requirements.The research result from this paper can provide references for the astigmatic design and experimental study of the rigidly connected joint between CFST T-shaped column and the steel beam, and lay foundations for further study of this type joint. |
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