Cold-formed steel under fire: Dual testing and empirical strength modeling

Abstract

This research investigates the structural behavior of cold-formed steel (CFS) under elevated temperature conditions, focusing on the response against both in-fire and post-fire effects. Through experimental analysis and empirical modeling, the study aims to specify the impact of temperature on the mechanical properties of CFS, specifically examining the changes in yield strength, ultimate tensile strength, and ultimate elongation. Tensile tests were conducted on CFS specimens of S235 and S355 grades exposed to temperatures ranging from 23 to 1000 °C, both during and after exposure to heating. Experimental findings revealed that yield strength and ultimate tensile strength decreased by up to 70% at 600 °C, 85% at 800 °C, and approximately 95% at 1000 °C during fire exposure, while post-fire conditions showed smaller decreases, with reductions of 15% at 800 °C and 30% at 1000 °C. In addition, empirical models, based on regression analysis and curve-fitting techniques, were developed to predict the yield strength variations of CFS, aiming to provide a supportive tool for predicting material behavior in fire scenarios. The empirical prediction models exhibit high accuracy in predicting post-fire conditions within a specific range of temperature, strength, and thickness but showed higher errors for in-fire conditions, emphasizing the complexity of material response under dynamic heating conditions. Validation of the prediction models involves an extensive analysis of previous studies, considering factors such as yield strength, specimen thickness, heating regimes, soaking times, and tensile loading rates. The results highlight the importance of considering especially initial yield strength and specimen thickness in predicting material behavior accurately. Overall, this research contributes to a deeper understanding of the sensitivity of steel material to elevated temperatures and provides substantial insights for enhancing fire safety assessments and structural design practices in the construction industry. The findings offer the baselines for developing more robust and reliable methodologies for evaluating structural performance in fire scenarios.

Graphical abstract

Keywords

cold-formed steel / fire resistance / elevated temperatures / empirical prediction model

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