New fire resistance design approach for concrete‐filled cold‐formed steel (CF‐CFS) built‐up composite column

Prior research investigated the fire resistance prediction of the concrete‐filled cold‐formed steel (CF‐CFS) built‐up columns when subjected to axial compression and high temperatures. However, a complex heat transfer analysis is needed to calculate the temperature development of the steel and concrete components of the composite cross‐section to predict the fire resistance of a composite column, as provided in EN1994‐1‐2. In order to estimate equivalent temperatures for the steel and concrete used in CF‐CFS built‐up column sections, this research provides a series of empirical formulae. A two‐dimensional heat transfer analysis calibrates a finite element model to estimate temperature across the CF‐CFS built‐up column sections. The concrete infill was simplified by separating into an inner and outer core. The empirical formulas' accuracy was assessed by comparing them with 2D heat transfer analysis results. Finally, the fire resistance of a CF‐CFS column was obtained using numerical simulation and compared with the analytical prediction following EN 1994‐1‐2 incorporated with the current empirical formulation. The results showed a high accuracy of the empirical formulation to determine the equivalent temperatures of the steel and concrete core components.