Tests of SHS brace-H-shaped chord X-joints under in-plane bending

This paper presented an experimental and numerical investigation on the square hollow section (SHS) brace-H-shaped chord X-joints under in-plane bending. A total of 8 specimens were tested to study the static behavior of the unstiffened and stiffened X-joints under in-plane bending. The test procedure, failure modes, load-vertical displacement curves, moment-rotation curves, load-deformation curves and strain intensity distribution curves were all reported. For the joints with 90°stiffeners, the bending ultimate capacity increased. However, for the joints with 45°stiffeners, the bending ultimate capacity decreased. Effect of external stiffener on initial stiffness of joints was unobvious. With the increment of β, the initial stiffness of joints under in-plane bending increased. The local deformation of the brace members of X-joints with big β was smaller than that of joints with small β. 90°stiffeners could delay the plasticity process of the joints with big β. 45°stiffeners could not delay the plasticity process of the joints with big β. The test results were compared with the design strengths calculated using the current Eurocode 3. It is shown from the comparison that the current Eurocode3 was generally conservative for the design of the SHS brace-H-shaped chord X-joints under in-plane bending. The FEA model of joints was validated by comparing test result with numerical result in the term of failure modes, load-vertical displacement curves and ultimate capacity.The effects of ratio of side length of brace to chord flange width β, ratio of chord flange width to double thickness of chord flange γ and ratio of brace to chord thickness τ on ultimate capacity of the joints were also numerically studied in parametric analysis. New design equations of ultimate capacity of SHS brace-H-shaped chord unstiffened X-joints under in-plane bending were proposed in this study which was proved to be more accurate and reliable.