Experimental study on the bearing capacity of Y-shaped concrete-filled steel tubular joints with plug-in connection under vertical load

To achieve a reliable connection between inclined columns and the supporting column with different cross-sections, a Y-shaped concrete-filled steel tubular (CFST) transfer joint was proposed, in which the double inclined columns and the supporting column were connected by a plug-in connection. Taking the steel tube thickness of the inclined columns, the diameter of the supporting column, the inserted depth of the inclined columns, and whether stiffening ribs were set in the intersection zone as parameters. Eight specimens of transfer joints with double square CFST inclined columns and a circular CFST supporting column were designed. The tests were conducted under vertical load. The failure modes, bearing capacity, deformation characteristics, and force mechanism were studied. The study results show that the core area of the joint with a plug-in connection scheme can effectively transfer the vertical load. The top surface of the core area is subjected to local pressure, and the diffusion region of the local pressure can extend to the supporting column. The lateral confinement effect of the core concrete in the intersection zone is significant to benefit the deformation and bearing capacity of this zone. The inserted depth of the inclined columns is the critical parameter affecting the mechanical properties. With the increased inserted depth, the bearing capacity of the joint represents a 18% growth in maximum, and the position where the steel tubes first reach the yield strain and where the local buckling first occurs can be changed. The stiffness and bearing capacity of the intersection zone can be increased by setting stiffening ribs. Then the failure position is shifted to other areas. The formulae for calculating the bearing capacity of Y-shaped transfer joints with double square inclined columns and a circular supporting column under symmetrical vertical load were proposed based on the mechanical characteristics of the joints obtained from the tests. The average ratio of the calculated results to the test results is 0. 879, and the standard deviation is 0. 049. The calculated results are safe, and the discreteness is small. © 2023 Science Press. All rights reserved.