Behaviour and design of cold-formed high strength steel RHS T-joints undergoing compression loads at elevated temperatures

Abstract

This study presents a comprehensive numerical program aiming to investigate the static resistances of cold-formed high strength steel (CFHSS) T-joints with square and rectangular hollow section (SHS and RHS) braces and chords at elevated temperatures. The included angle between brace and chord members was 90°. The static behaviour of simply supported SHS and RHS T-joints undergoing compression loads through brace members was investigated at four elevated temperatures, including 400°C, 500°C, 600°C and 1000°C. The mechanical properties at elevated temperatures given in the literature for cold-formed S900 steel grade tubular members were used in this study. The numerical investigation was performed using the finite element (FE) models developed and validated by Pandey et al. [1] and Pandey and Young [2] for cold-formed S960 steel grade T-joints at ambient temperature and post-fire conditions. In total, 756 FE T-joint specimens were analysed in this numerical study, including 189 FE T-joint specimens for each elevated temperature. The tubular T-joint specimens were failed by chord face failure, chord side wall failure and a combination of these two failure modes. The resistances of investigated T-joints at elevated temperatures were compared with the nominal resistances predicted from design rules given in European code and CIDECT using the mechanical properties at elevated temperatures. Overall, it is shown that the current design rules given in European code and CIDECT are uneconomical and unreliable. As a result, economical and reliable design rules are proposed in this study through two design approaches for predicting the resistances of cold-formed steel SHS and RHS 90° T-joints of S900 grade at elevated temperatures.