Study On Shear Behavior Of Precast Steel Tube Confined Frame Joints

In this paper,a prefabricated assembly type steel pipe joint connection mode is proposed.The new node is composed of core skeleton,restrained steel pipe and extension beam.It can improve the lateral constraint of the joints,the strength and ductility of the concrete in the core area,and realize the seismic concept of strong joints and weak components.In order to promote the engineering application of the new type of assembled beam column joints,the shear performance of the precast assembled steel pipe beam column joints is systematically studied in this paper by the combination of experimental and numerical analysis.The specific research work includes:(1)The experimental study on three prefabricated steel tube constrained frame joints and one cast-in-place joints under reciprocating load is carried out by taking the thickness of steel tube and column axial compression ratio as the main parameters in the core area.The failure mode of the cast-in-place frame joints is the concrete shear failure in the core area,and the precast assembly type steel tube constraint node has improved the concrete bearing capacity of the core area because of the concrete restraint of the steel tube to the core area,and the steel pipe bears some shear force.The joints all show the plasticity of the beam end after the yield of the restrained steel tube.The hinged beam destroys the shape.Prefabricated steel tube confined joints show good load carrying capacity and energy consumption,and the shear capacity is increased by about thirty percent compared with the corresponding cast-in-place joints.Due to the failure of the precast joints in the test,the bearing capacity of the measured precast joints is similar.With the increase of the thickness of the restrained steel pipe and the reduction of the column axial compression ratio,the bearing capacity of the precast joints is slightly improved.In addition,the ductility coefficient of the prefabricated steel pipe is nine percent to thirty-five percent higher than that of the cast-in-place node,and the ductility coefficient of the assembled node increases with the decrease of the thickness of the restrained steel pipe and the increase of the column axial compression ratio.(2)On the basis of the reasonable determination of the constrained concrete constitutive model and the contact setting between the restrained concrete and the core parts of the confined concrete and core areas,the finite element software ABAQUS is used to establish and verify the numerical model of the shear performance of the prefabricated steel tube constrained joints.By using the finite element model,the working mechanism of prefabricated and cast-in-place joints is analyzed.The stress distribution,hysteresis curve,strength and stiffness degradation and energy dissipation capacity are compared and analyzed.It is concluded that the prefabricated assembly node and the cast in situ node are basically the same in earthquake energy dissipation capacity,and the prefabricated assembly joints are rigid.The results show that the precast and fabricated joints can meet the design requirements of cast-in-place connections.(3)Based on the numerical analysis model,the main parameters affecting the shear resistance of the precast assembled steel tube constraint frame joints are analyzed.The main parameters are the column axial compression ratio,the core area concrete strength,the restrained steel tube thickness and the yield strength.The results of the parameter analysis show that the shear strength of the prefabricated steel tube constraint joints increases with the increase of the concrete strength of the core,the thickness of the restrained steel tube and the yield strength of the restrained steel tube,and the axial compression ratio of the column is not much affected,but the increase of the axial compression ratio makes the whole joint test.The deformation ability of the piece is reduced.