Quantifying Vertical Temperature Non-Uniformity for Cold-Formed Steel Structural Fire-Resistant Design

The time–temperature curve serves as a fundamental input for calculating structural fire resistance. Accurate acquisition of this curve is essential for designing structures to withstand fire incidents effectively. In this study, fire test temperature variation data were analyzed to develop a comprehensive understanding of the temperature-rise curve, categorized into three primary phases: Confined Fire Phase, Reignition Phase, and Flashover to Fully Developed Fire. To address non-uniform temperature distribution, a temperature reduction coefficient was introduced into the temperature-rise curve formula. This coefficient was derived by fitting experimental temperature data from multiple fire tests, enhancing the formula’s applicability to compartment fires. Furthermore, accounting for non-uniform temperature distribution along compartment height is critical for accurate thermo-mechanical simulations of structural components. To simplify calculations, layer-specific reduction coefficients were proposed: top area (x ≥ 0.7H): 1.0; middle area (x < 0.7H): 0.73; bottom area (x ≤ 0.4H): 0.34. These coefficients, determined through numerical simulations, exhibit broad applicability. In conclusion, precise characterization of temperature-rise curves is vital for structural fire resistance assessment. The proposed methodology and reduction coefficients improve the robustness and generalizability of thermo-mechanical simulations in evaluating structural fire performance.