| Special-shaped concrete-filled tubular column structure were evolved on the basis of the special-shaped reinforced concrete column structure, the biggest advantage of such structure is to improve the bearing capacity and ductility of core concrete by the use of outsourcing steel pipe and solve the problem that ordinary special-shaped reinforced structure can not be applied in multi-storey and tall buildings and areas of high seismic fortification intensity, meanwhile, it owns the advantage that the thickness of ordinary special-shaped column limbs can be the same as that of the wall, which can avoid the appearance of column base in the wall surface. Because of the merits, a wide development prospect will appear in this kind of structure. In recent years, there are few achievements of domestic and abroad scholars on beam to special-shaped concrete-filled tubular column joints. Moreover, most of them have focused on the research of steel beam to special-shaped column connections, the studies on the connection forms between special-shaped concrete-filled tubular column and reinforced concrete beam and mechanical and earthquake resistance behavior of such joints are not yet reported. Supported by 2012 Hubei Province Natural Science Fund Project(2012FFB05112) and 2014 Central University Fundamental Research Funds Project(WUT2014-IV-125), based on the existing research results of studying team, the extended-end-plate joints and stiffening ring joints of T-shaped concrete-filled tubular column with reinforced concrete beam are designed and manufactured. This paper emphasizes on the study of the mechanical and earthquake resistance behaviors of two types of joints by experimental study, finite element numerical simulation and theoretical analysis method. The main contents and conclusions are shown as follows:(1) In accordance with the ratio of 1:2, considering the influencing factors of length of corbel, thickness of end-plate, diameter of high-strength bolt, configuring stiffener or not, diameter of ring rib and setting mode of ring rib, 10 extended-end-plate and 7 stiffening ring joints are manufactured. Through static and low-cycle repeated loading test, the failure mode and internal force transfer mechanism are discussed, the load-displacement hysteresis curves, skeleton curves, displacement and beam-column rotation ductility, energy dissipation abilities are analyzed. According to test parameter analysis, the influence of degree of factors on the bearing capacities and energy dissipation abilities are determined, and then the design recommendations and structural measures are put forward. The test results show that two types of joints have the feature of clear force transfer mechanism, the failure mode reveals that the destructions of joints are derived from the development of plastic hinges formed at the end of corbel on the beam. The shapes of hysteresis curves of all specimens are full, extended-end-plate joints present inverted “S”, the equivalent damping factors eh are between 0.147 and 0.176, displacement ductility factors ?? are 3.48 to 6.29. The shapes of hysteresis curves of stiffening ring joints present arch, the equivalent damping factors eh are between 0.199 and 0.262, displacement ductility factors ?? are 2.88 to 4.51. The maximum shear angles of two types of joints are between 0.796% and 4.488% of beam-column relative ultimate angles, there is a little influence of the shear deformation of joint region on the structural deformation. Each of specimen possesses good earthquake resistance capability.(2) By analyzing and fitting the skeleton curves and hysteresis curves of specimens measured by test, adopting dimensionless method, the restoring force models are established. The modes are composed by tri-linear skeleton curve model, stiffness degradation and hysteresis rule. The skeleton curves and hysteresis curves obtained from the tests are compared with the curves calculated by the restoring force models, the comparison results prove the correctness of restoring force models established in this paper.(3) By using nonlinear finite element analysis software ABAQUS, the simulation and research on the mechanical properties and earthquake resistance behaviors of joints under monotonic and reciprocating load are carried out, in order to verify the finite element model, the calculation results and experimental data are compared. The development of cracks and variation of the shear stress are revealed by analyzing the working mechanism and stress distribution of joints. On the basis, the study of the axial compression ratio, linear stiffness ratio of beam and column, concrete strength and reinforcement ratio of frame beam on the mechanical properties of nodes is conducted. The analysis results show that the simulation calculations of load-displacement curves can agree well with the experimental data, the shear forces of joints are borne mainly by compression strut formed in core region, a small proportion is shared by the corbel web. Configuring stiffener can suppress the deformation caused by the bulging of extended-end-plate effectively and reduce stress concentration intensity of joint zone. For the stiffening ring joints, when load on beam extremity reaches ultimate load, the cross-section of steel pipe outside of the corbel flange yields remarkably, the buckled area is within the range of one-third height of beam, in order to enhance the joint, the steel pipe in this range should be thickened locally. The axial compression ratio and linear stiffness ratio of beam and column have a little influence on the bearing capacities of the two types of joints, however, with the linear stiffness ratio increasing, the initial stiffness of stiffening ring joints appear a certain degree of losses. Increasing the concrete strength of frame beam, the bearing capacities of the two types of joints are improved obviously, among them, the stiffening ring joints are far more significant. With the improvement of reinforcement ratio, the flexural capacities of the two types of joints are increased significantly, but when the reinforcement ratio of the frame beam is more than 1.8%, the amplitude of increasing of the bearing capacity is very small.(4) On the basis of experimental and theoretical studies, considering the influence of thickness of end-plate, diameter of bolt and stiffener on the flexural capacity of the extended-end-plate joint, a formula used for calculating the type of high-strength bolt and the size of end-plate is established. Through analyzing the internal force transfer mechanism of the two types of joints, a method to calculate the horizontal shear is presented. Considering the axial pressure, pre-tensioning force of high-strength bolt and the flange portion of concrete, the formula for predicting shear capacity of the two types of joints is proposed, and then, the calculation results of the formula and experimental data of related literature are compared, the result indicates that the calculated values and experimental values of the bearing capacity are basically consistent.The achievements of the research will provide experimental evidence and theoretical support for Technical Specification for Structures with Special-shaped Concrete-filled Steel Tubular Members.Based on the generalization of the paper, the research prospects about the project are brought up. |
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