Behaviour of CHS brace-to-H-shaped chord X-joints under in-plane bending

This paper presents an experimental investigation on the circular hollow section (CHS) brace-to-H-shaped chord X-joints under in-plane bending. A total of six specimens was tested, in which three specimens were reinforced with the internal stiffeners in the H-shaped chord. The load carrying capacities, failure modes, axial load-vertical displacement curves, bending moment-rotation curves, axial load-local deformation curves and strain distribution curves of all specimens were reported. The corresponding finite element analysis was also performed and calibrated against the test results. Therefore, an extensive parametric study was carried out to evaluate the effects of main geometric parameters (β, 2γ and τ) on the behaviour of CHS brace-to-H-shaped chord X-joints. It is shown from the comparison that the load carrying capacities of the joints with small β value (β < 0.605) under in-plane bending are effectively enhanced with the increase of the β value, whereas the β has little influence on the in-plane flexural behaviour of the joints with large β value (β ≥ 0.605). Furthermore, the ductility of the joints without the internal stiffeners in the H-shaped chord increases remarkably with the increase of the β value, and the increment of the ductility of the joints without the internal stiffeners is more pronounced than their counterparts with the internal stiffeners. It is shown from the comparison that the current Eurocode is generally unconservative for the design of CHS brace-to-H-shaped chord X-joints with small β value under in-plane bending. The new design equations were proposed in this study which was verified to be more accurate.