Tests of concrete-filled circular hollow section X-joints with curved chord under in-plane bending

This article presents the static tests on bare and concrete-filled circular hollow section X-joints with curved chord under in-plane bending. A total of 16 specimens were fabricated by hot-rolled bending the chord members into curvature with three different radii to apply in-plane bending to the brace members, in which six specimens were tested with bare curved chord, six specimens were tested with concrete filled in the curved chord only, and four traditional bare and concrete-filled circular hollow section X-joints with straight chord were also tested for comparison. The effects of curvature radius of chord member, concrete filled in the chord member and cross-section dimension of brace member on the joint strength, and behaviour under in-plane bending were evaluated. The curvature radius of chord member generally has insignificant influence on the in-plane flexural behaviour of circular hollow section X-joints with large radius. However, the ultimate strengths of circular hollow section X-joints under in-plane bending are greatly weakened by hot-rolled bending the chord members into curvature with small radius. Furthermore, the reinforcement of filling the concrete in the chord member has insignificant influence on the in-plane flexural behaviour of circular hollow section X-joints. On the other hand, the cross-section dimension of brace member has significant effect on the ultimate strengths of circular hollow section X-joints under in-plane bending. In addition, the current design rules are quite conservative for the design of bare and concrete-filled circular hollow section X-joints with curved and straight chord under in-plane bending loading.