EXPERIMENTAL STUDIES ON LOAD-TRANSFERRING MECHANISM OF CFST DIRECTLY-WELDED K-JOINTS WITH STUDS

The behaviors of Concrete-filled steel tubular (CFST) directly-welded K-Joints with studs on the inner wall of the main steel tube (inner stud) were tested, as well as a specimen without stud for comparison. During the test, the main tube was under axial pressure, while the two web members were equivalently and simultaneously under a pressure and a tension, respectively. The results show that for the buckling failure of web member, the load-displacement curve of compressive web member consists of a linear elastic stage and an elastic-plasic stage. With or without studs, the strains of the main tube in welding area are larger than those in other areas, whose load-strain curves include linear elastic stage and elastic-plasic stage, while the strains in the other areas are in elastic state. The stain distribution of stud does not change, but the stress magnitude is reduced, indicating that the studs are able to transfer force from steel tube to core concrete, especially at the strain concentration area. In the axial direction of main tube, strain concentration are observed at the two sides of the center section of joint, with a range of 2.7 times of the side tube diameter. In the circular direction, strains mainly concentrate in an area between directions -60° and 60°. It is suggested that the inner studs should be arranged mainly on these longitudinal and transverse areas, and sparsely or not arranged outside.