Modelling and design of cold-formed S960 steel brace-rotated tubular T- and X-joints

This paper presents detailed numerical investigation and design of cold-formed S960 steel grade brace-rotated (BR) tubular T- and X-joints. The BR tubular joint is one of the novel bird-beak tubular joint configurations, where the rotation of brace member(s) enhances joint resistance and aesthetic appearance. The numerical investigation was performed through finite element (FE) analysis. The tests carried out by the authors were used to develop accurate FE models of BR T- and X-joints, which in turn precisely replicated the joint resistances, load vs deformation curves and failure modes of test specimens. With an aim to broaden the data size, a comprehensive FE parametric study was performed using the verified FE models. The nominal resistances predicted from the literature and European code were compared to the joint failure resistances of 211 BR T- and X-joints specimens, including 192 FE specimens investigated in this study. The BR T- and X-joint specimens were failed by two failure modes, namely chord face failure (F) mode and a combination of chord face and chord side wall failure mode, i.e. combined failure (F + S) mode. It has been shown that the existing design provisions are unsuitable for the design of cold-formed S960 steel grade BR T- and X-joints investigated in this study. Hence, using three design approaches, accurate, less dispersed, reliable and user-friendly design equations are proposed in this study to estimate the joint failure resistances of cold-formed S960 steel grade BR T- and X-joints.