Stainless steel box columns in fire analysis and design recommendations

Abstract: The use of stainless steel in buildings is small but increasing, mainly due to the low maintenance costs, favourable corrosion resistance and aesthetic appearance. It is well known that stainless steel also performs better than carbon steel at elevated temperatures. The improved behaviour is mainly explained by the enhanced material properties and a favourable temperature dependent relationship between strength and stiffness that makes stainless steel less prone to buckling in fire. The objective of this work is to establish and validate a simple design model for Class 4 stainless steel box columns in fire. The proposed design model is verified through parametric studies performed with the finite element software Abaqus and the FE-model used for the parametric studies is validated towards Class 4 stub column tests at both room and elevated temperatures. The failure mode of Class 4 box columns is a combination of local and flexural buckling. The importance of taking the temperature dependent relationship between strength and stiffness into account is clearly seen in the results from the parametric study. The proposed design model is fully consistent with EN 1993-1-1 (2005) and its capability to predict failure loads at different steel temperatures is compared to the design model in EN 1993-1-2 (2005) and EN 1993-1-4 (2006) as well as the Design Manual for Structural Stainless Steel (2006). All design models are then compared to the results of the parametric study. The results show an improvement from a mean of 0,96 and COV=0,17 to a mean of 0,99 with a COV=0,12. Furthermore the proposed design model gives better results than the existing models for all cross-section classes when compared to all available test results.