Fire resistance of slender section beams

Abstract

The paper shows experimental and numerical research into slender cross‐section beams in case of fire. The topic is very important because little investigation has been made and little experimental data has been collected so far. In the framework of the RFCS project FIDESC4 – Fire Design of Steel Members with Welded or Hot‐rolled Class 4 Cross‐sections, several simple supported beams were tested at elevated temperature at the Czech Technical University in Prague.Currently, Eurocode 3 contains a number of simple rules for design of slender Class 4 cross‐sections which, based on recent numerical simulations, proved themselves to be over‐conservative. Through refining these rules, material savings could be achieved, which would lead to greater competitiveness of the steel structures. This is being covered in existing research, but is not published in this paper, which is limited to lateral torsional buckling behaviour only.Determination of the bending resistance for members subjected to lateral torsional buckling of Class 1–3 cross‐sections at elevated temperature is based on the same principles as the design at room temperature, according to EC 3 part 1‐1 [1]. However, it differs in using only one imperfection factor for all types of cross‐sections. The informative Annex E of the standard (EC 3 part 1‐2 [2]) recommends using the design formulas for slender (Class 4) sections as well. But there is a restriction of the critical temperature value and a different reduction of yield strength is used (0.2 % proof strength for Class 4 instead of 2.0 % proof strength for stockier Class 1–3 sections). For the non‐uniform members (variable section height), a limited design procedure is given in EC 3 part 1‐1 [1]. This is applicable for room temperature only. The possibility of using these rules for fire design is not yet confirmed.

Experimental Study of Lateral-Torsional Buckling of Class 4 Beams at Elevated Temperature

“…This may be due to the insufficient number of experimental tests that were carried out for the lateral-torsional buckling of Class 4 beams. This applies both for the room and elevated temperature [5].…”

“…In the case of four girders, the beams have been protected against lateral buckling, while in the remaining three cases the elements were exposed to the risk of global stability loss. The computer simulations developed based on the results of above-mentioned experiments have been presented in [5,6], and in the case of web-tapered beams in [7]. It has to be noted, that results and assumptions for further research conducted within the framework of FIDESC project, covering four compressed columns with slender web, have been presented in [8].…”