10.09: Critical temperatures of members with class 4 cross‐section

This paper describes a numerical investigation on the critical temperatures of members with Class 4 cross‐sections according to Eurocode 3 design. For such sections, the norm suggests the use of a default critical temperature of 350 °C irrespective of the load level conditions if no other calculation is made. On that regard, the authors have previously demonstrated that this temperature might be too conservative for certain conditions, especially if different degrees of utilization are taken into account. As a consequence, the authors recommended and validated new default critical temperatures for Class 4 cross‐sections subjected to compression and bending about the major axis, for different reduction factors for the design load level under fire conditions. Building up on said studies regarding slender cross‐sections, the present work aims at extending and establishing the groundwork for future studies on the critical temperature of members subjected to fire with the ultimate goal of achieving and validating a wide‐reaching proposal of more appropriate default critical temperatures for steel members and cross‐sections subjected to fire. From this study it was observed that the critical temperatures for laterally restrained members (in‐plane) are in agreement with those proposed in previous research by the authors. The out‐of‐plane simulations, however, displayed similar patterns to those of their in‐plane counterparts up until a certain slenderness threshold, after which a noticeable loss of resistance seems to occur, likely due to the higher influence of second‐order effects in the out‐of‐plane direction.