The General Method for the fire design of slender I-section web-tapered columns

Abstract

The purpose of this paper is to validate the General Method for the stability check of unrestrained I-section web-tapered columns in fire situation. The General Method (clause 6.3.4 of EN 1993-1-1) covers the safety check of structural elements with complex support conditions and/or of non-prismatic members. However, the fire part of the Eurocode 3 (EN 1993-1-2) gives no further indication regarding the applicability of the method at elevated temperatures, apart from adapting the methodology to fire using the reduction factors for steel material properties, which is identified as a gap in the current version of the norm. To ascertain the validity of said adaptations, the ultimate capacity of members at elevated temperature has been obtained numerically with GMNI-Analyses and a parametric investigation incorporating I-section web-tapered columns built from slender (class 4) cross-sections has been carried out, with special attention to the influence of local buckling on member stability. It has been demonstrated that a straightforward application of the temperature-reduced mechanical properties of steel in the General Method results in an unsafe methodology, therefore justifying improvements to the procedure. In this work, this is done by i) proposing a novel methodology for the calculation of the in-plane load amplifier αult,k and ii) recalibrating the EN 1993-1-2 buckling curve. Not only does this new procedure improve the accuracy of the methodology but it also foregoes the otherwise necessary evaluation of the critical cross-section along the column.