Post-Fire Flexural Behavior of Cold-Formed Steel Built-up Beams with Stiffeners and Fire-Resistant Coatings: Experimental and Numerical Study

The design and construction of thin-gage steel sections have advanced over recent years. However, research on structural stability and safety against fire mishaps remains limited. This investigation focuses on the post-fire response of cold-formed steel (CFS) structural elements under restrained support conditions. Additionally, the effect of stiffeners on structural integrity and stability is examined. The fire-resistant design of CFS structures is still under development, and there is no evidence of proper guidelines for built-up sections. Moreover, studies related to structural elements exposed to elevated temperatures are limited. The proposed study evaluates the post-fire flexural performance of CFS back-to-back C-section beams in alignment with the ISO 834 fire curve. A back-to-back arrangement is used, with connections made through electric arc welding. Sixteen specimens were fabricated, subjected to heating in a furnace for 60 minutes at 925 °C and for 120 minutes at 1029 °C, and tested under a four-point loading condition while considering different cooling regimes. The edges of the beams were restrained to prevent lateral torsional buckling failure. Transverse stiffeners were connected by welding to the web of the beam to enhance section capacity and improve buckling behavior. Additionally, the effect of fire-resistant coating on CFS beams was analyzed to assess improvements in beam durability. Load-deflection, load-strain, and stiffness of the section were validated. ABAQUS was used to perform finite element method (FEM) analysis, and the results were analyzed with the experimental outcomes. The moment capacity was also calculated using the direct strength method (DSM) and compared with experimental findings. The addition of stiffeners improved the section capacity by 20% in the case of reference specimens. At higher durations of heating (120 mins), there is an increase in section capacity of 40.42% for air-cooled specimens and 33.26% for water-cooled specimens. The effect of fire-resistant coating influences the behavior and load-carrying capacity of beam specimens. Expanded perlite-coated air-cooled specimens exhibit better strength improvement of about 38% when compared to uncoated specimens, and there is no evidence of reduction in strength observed up to 60 minutes of heating. Considering both the cases (with and without stiffeners), air-cooled specimens outperformed water-cooled specimens by almost 15% to 25%.