Local-global buckling interaction in steel I-beams—A European design proposal for the case of fire

• Comprehensive review of European fire design rules for steel beams with thin-walled I-sections. • Modifications to the Effective Width Method at elevated temperatures for improved section capacity assessment. • The Effective Section Factor for improved account of the local-global buckling interaction. • Better estimation of the non-uniform bending distributions using the factor “f”. • Comparison of the existing Eurocode 3 Part 1–2 (EN1993-1-2:2005) rules with the improvements in the second generation of Part 1–2 of Eurocode 3 (FprEN1993-1-2:2023). This paper presents a comprehensive review of the developments leading to the proposal of European fire design rules for steel beams with thin-walled I-sections. Thin-walled beams are favoured in steel construction due to their structural efficiency, however they are prone to buckle when subjected to in-plane loads, phenomenon which requires a thorough investigation. The focus lies on addressing the interaction between local and global buckling in these members. This study discusses modifications to the Effective Width Method at elevated temperatures, aiming to rectify underestimation of section capacity on certain cross-sections. Additionally, an overview of lateral-torsional buckling resistance is provided, being a new Effective Section Factor proposed to account for its interaction with local buckling. The paper revisits the European fire design proposal, comparing the improvements of the existing Eurocode 3 Part 1–2 (EN1993-1-2:2005) relative to the recent second generation of Part 1–2 of Eurocode 3 (FprEN1993-1-2:2023) through an extensive numerical study. Limitations and future research directions are also discussed, such as dependency on the section classification and broadening the application scope of these rules to higher steel grades.