Tests of bare and concrete-filled CHS T-joints with concave chord under axial compression

A series of tests were conducted on bare and concrete-filled circular hollow section (CHS) T-joints with concave chord under axial compression. A total of 16 specimens were fabricated by hot-rolled bending the chord members into curvature with three different radii to apply axial compression force to the brace members, in which 6 specimens were tested with bare concave chord, 6 specimens were tested with concrete filled in the concave chord only, and 4 traditional bare and concrete-filled CHS T-joints with straight chord were also tested for comparison. The joint strengths, failure modes, axial load-vertical displacement curves, axial load-chord deformation curves and strain distribution curves of all specimens are reported. The effects of curvature radius of concave chord and concrete filled in the chord member on the joint strength and behaviour were evaluated. It is shown from the comparison that the ultimate strengths of the CHS T-joints with concave chord are generally larger than those of the traditional CHS T-joints with straight chord. Furthermore, the ultimate strengths of CHS T-joints with concave chord are significantly enhanced by filling the concrete in the chord member only, and the enhancement of the ultimate strengths of the CHS T-joints with large β ratio is much more pronounced than that of the CHS T-joints with small β ratio. It can be generally concluded from the comparison between the test strengths and the design strengths that the current design rules are generally conservative for both traditional bare CHS T-joints with straight chord and bare CHS T-joints with concave chord.