Advisory Desk Note 546 Critical temperatures for compression members in the UK NA to BS EN 1993-1-2

Publication Year

2025

Document Status

Current

Abstract

This SCI Advisory Note clarifies the limitations of using critical temperature values from the UK National Annex to BS EN 1993-1-2, particularly Table NA.1, for compression members in fire design. The tabulated values assume an imperfection factor of 0.49 (buckling curve 'c'), appropriate for UC sections in S355 buckling about their minor axis. However, this assumption is not conservative for members with lower imperfection factors—such as UB sections, hot finished hollow sections, or higher-grade steels—commonly found in trusses, bracing, or frames. The note presents replacement critical temperatures for hollow sections in S355 with a = 0.21 and advises designers that both UK NA and ASFP Yellow Book guidance may be unconservative for members not meeting the curve 'c' assumption.

Document History

July 2025 edition.

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