Bending Behaviour of CHS X-Joints with Curved Chords

This paper explores the static and cyclic behaviours exhibited by X-joints fabricated from circular hollow sections (CHS) incorporating curved chords under bending loading. First, a finite element (FE) model of CHS X-joints was established, and the accuracy was validated by the test results. Then, the influence of the geometric parameters on the ultimate capacity of these joints was deeply conducted through variable parameter expansion analysis, including the chord curvature (R)-to-diameter (D) ratio α, brace diameter (d)-to-chord diameter (D) ratio β, and chord diameter (D)-to-double thickness (2T) ratio γ. In addition, the formulae for the in-plane bending bearing capacity of CHS X-joints with curved chords were examined based on the FE results and typical design guides. Finally, the hysteresis performance of the joints was investigated to modify such formulae. The results show that (1) the bending bearing capacity decreases with increasing α when 3 ≤ α ≤ 12 and changes slightly when α > 12. The bending bearing capacity increases with increasing β and decreases with increasing γ. (2) The bending bearing capacity design formula is modified by FEM results on the basis of the formula derived from Eurocode 3. The API-WSD and LRFD design codes do not consider the effect of γ, and the AIJ seems to be overly conservative. (3) In light of the hysteresis analysis, the smaller the magnitude of γ and the larger that of β, the more favourable the bending load-bearing capacity, ductility coefficient and plastic deformation capability of the joints are found to be. The bending bearing capacity under cyclic loading was close to the value under static loading when α ≥ 9, whereas a reduction coefficient of 0.9 was considered when α < 9. Comparison analyses indicated that the adjusted design formula was suitable for engineering design.