Behaviour of bird-beak square hollow section X-joints under out-of-plane bending

An experimental investigation was conducted on bird-beak square hollow section (SHS) X-joints under out-of-plane bending. A total of nine specimens including traditional SHS X-joints, square bird-beak SHS X-joints and diamond bird-beak SHS X-joints were tested. The test results of joint strengths, failure modes, load-vertical displacement curves, bending moment-local deformation curves, bending moment-rotation curves, and strain distribution curves of all specimens were reported. The corresponding finite element analysis (FEA) 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, τ and 2γ) on the behaviour of bird-beak SHS X-joints under out-of-plane bending. It was shown from the comparison that the ultimate strengths and initial stiffness of all specimens under out-of-plane bending significantly increased with the increase of the β ratio. The ultimate strengths of bird-beak SHS X-joints under out-of-plane bending are generally much larger than those of traditional SHS X-joints. Furthermore, the ultimate strengths of diamond bird-beak SHS X-joints under out-of-plane bending are always larger than those of square bird-beak SHS X-joints. The joint strengths obtained from the experimental investigation were compared with the design strengths calculated using the current Eurocode 3 and IIW Specification for traditional SHS X-joints under out-of-plane bending, which were demonstrated to be quite conservative. In addition, the design equations are proposed for bird-beak SHS X-joints under out-of-plane bending, which were shown to be accurate and reliable.