Design of cold-formed high strength steel rectangular hollow section T-joints under post-fire conditions

A comprehensive numerical investigation looking into the static post-fire structural performance of cold-formed high strength steel (CFHSS) T-joints is presented in this paper. The braces and chords of T-joints were made of square and rectangular hollow section (SHS and RHS) members. The steel grade of SHS and RHS members was S960 with nominal 0.2% proof stress of 960 MPa. The static strengths of SHS and RHS T-joints were investigated corresponding to four post-fire temperatures, including 300°C, 550°C, 750°C and 900°C. Pandey and Young [1] carried out tests to investigate the post-fire residual strengths of cold-formed S960 steel grade SHS and RHS T-joints. The test results were used to develop an accurate finite element (FE) model. Using the validated FE model, a comprehensive FE parametric study was performed in this investigation. The validity ranges of critical geometric parameters were extended beyond the current limits mentioned in international codes and guides. The nominal resistances predicted from design equations given in EC3 [2] and CIDECT [3], using post-fire material properties, were compared with a total of 765 test and FE joint resistances, including 756 numerical data obtained in this study. Overall, SHS and RHS T-joint specimens were failed by chord face failure, chord side wall failure and a combination of these two failure modes. Generally, the current design rules in EC3 [2] and CIDECT [3] are quite conservative and largely dispersed. As a result, accurate, less dispersed and reliable design equations are proposed in this study.