S960 steel grade square bird-beak T- and X-joints: Numerical investigation and design

The detailed numerical investigation and design of cold-formed S960 steel grade square bird-beak (SBB) T- and X-joints have been presented in this paper. The SBB joint is one of the novel bird-beak tubular joint configurations and obtained by rotating the chord member of a conventional square hollow section (SHS) joint along its centroidal axis by 45 degrees. In this investigation, accurate finite element (FE) models were developed for SBB T- and X-joints using the tests carried out by the authors. The developed FE models successfully replicated the static strengths, load vs deformation curves and failure modes of test specimens. In order to gain an in-depth understanding on the static behaviour of SBB joints, a comprehensive FE parametric study was performed using the verified FE models. The joint failure strengths and joint ultimate capacities of a total of 220 SBB T- and X-joints specimens, including 200 FE specimens investigated in this study, were evaluated against the nominal strengths predicted from the literature and European code. All SBB T- and X-joints test and FE specimens were failed by the chord crown failure (C) mode. It has been shown that the design provisions given in the literature and European code are unsuitable and uneconomical for the design of cold-formed S960 steel grade SBB T- and X-joints investigated in this study. Therefore, accurate and reliable design equations are proposed in this study for predicting the static strengths of the investigated SBB T- and X-joints.