Behaviour of steel-concrete-steel SHS X-joints under axial compression

This paper presents the experimental investigation and finite element analysis on double-skin square hollow section (SHS) X-joints under axial compression, which were strengthened with concrete filled in the chord between inner tube and outer tube. A total of 22 orthogonal SHS X-joints with different brace to chord width ratio (β), hollow ratio of chord (χ) and shapes of inner tube of chord were tested, in which two traditional SHS X-joints and two concrete-filled SHS X-joints were tested for comparison. The effects of brace to chord width ratio (β), inner tube to outer tube thickness ratio of chord (ω), hollow ratio of chord (χ), shape of inner tube of chord and strength of concrete infill on the structural behaviour of steel-concrete-steel SHS X-joints under axial compression were evaluated. It is shown from the comparison that the inner tube and concrete infill significantly enhanced the ultimate strengths of SHS X-joints under axial compression. Furthermore, the ultimate strength and initial stiffness of steel-concrete-steel SHS X-joints under axial compression are improved with the increase of inner tube to outer tube thickness ratio of chord (ω) and strength of concrete infill. On the other hand, the ultimate strength and initial stiffness benefit from the increase of the β ratio and decrease of the χ ratio. The design equations are proposed based on the test and numerical results for steel-concrete-steel SHS X-joints, which were verified to be more accurate.