Study On The Vertical Loading Behavior Of The Y-shaped CFST Transfer Joint Under Bending Moment Of Beams

With the development of modern high-rise and super high-rise buildings,the application of transfer floors becomes more and more widely,because of the general requirements of structures and building schemes with complex profiles and diverse functions.The concrete-filled steel tubular inclined column transfer structure combines the advantages of concrete-filled steel tubular(CFST)members and inclined column transfer structures.It has the advantages of high bearing capacity,clear force transfer path,and small cross-section size of members,which is beneficial to the full utilization of building space and the improvement of economic benefits,so it should have a wide application prospect.In this paper,the vertical loading tests of CFST Y-shape transfer joints proposed by the research group were carried out under the fixed bending moment applied at the beam ends,and the finite element analysis software ABAQUS was adopted to analyze the behavior of the specimens.The failure mode,bearing capacity,deformation characteristic,and force transfer mechanism of the joints were studied.The effects of the variables on the mechanical properties of the joints were analyzed.The study results of this paper have not only important academic value for improving the theoretical system of the mechanical properties of CFST Y-shaped transfer joints under complex working conditions but also provide theoretical basis and design reference for engineering practice.The specific work and main conclusions of this paper are as follows:(1)Three specimens through which vertical loads are transferred by a horizontal diaphragm plate(designated as "the horizontal diaphragm plate type"),and one specimen through which vertical loads are transferred by vertical ribbed plates(designated as "the vertical ribbed plate type"),were designed.The insertion depths of the first three specimens were different.The vertical loading tests of the specimens under the fixed bending moment applied at the beam ends were carried out.The test results show that the designed joint can meet the design principle of "strong joint and weak members".The asymmetrical force transfer behavior of the inclined columns can be found under the combined action of bending moment and vertical loads.It leads to a more complex stress state in the intersection area of two inclined columns and the core area of the joint.With the same insertion depth,the stiffness of the core area of the horizontal diaphragm plate type joints is higher than that of the vertical ribbed plate type joints.(2)The mechanical properties of the joints were analyzed by using the finite element software ABAQUS.By comparing the finite element analysis results with the test results,it shows that the finite element model can well predict the failure mode and bearing capacity of the joints.Under the condition that the accuracy of the finite element model is verified,the influence of variables on the mechanical performance of the joint area was further studied.The analysis results show that both the inclined columns and the intersection area of two inclined columns are in the state of eccentric pressure,and the top surface of the core area of the joint is subjected to uneven local force transferred from the intersection area.(3)Based on the results of the tests and the finite element analysis,the design methods of the intersection area of two inclined columns and the core area of the joint under the eccentric compressive state were proposed.The calculated results are in good agreement with the results of finite element analysis.