A scaling law for fire duration in RC frames to resist fire-induced progressive collapse: Considering critical design parameters

Fire is a significant factor that can lead to progressive collapse in structures. Due to spatial limitations, scaled models are often employed in collapse experiments. However, traditional similarity laws for fire testing require scaled models to experience heating rates much higher than those of the prototype, which is difficult to achieve with standard fire furnaces. This study addresses this challenge by conducting numerical analyses on geometrically scaled reinforced RC beam-column structures. A unified similarity law for fire duration is proposed, incorporating key design parameters such as span-depth ratio, reinforcement ratio, and concrete cover thickness. This law enables scaled models to replicate progressive collapse behavior of RC prototype frames. The results reveal that similar mechanical performance can be achieved when rebar and average beam-section temperatures are comparable, despite variations in internal concrete temperatures. Additionally, smaller span-depth ratios cause more severe beam damage under fire exposure. Increasing span-depth ratios from 10 to 12 and 14 has minimal impact on load capacity at ambient temperature. However, smaller span-depth ratios result in higher ultimate load capacity after prolonged fire exposure. These findings provide a practical approach for scaling fire-induced collapse experiments and highlight the role of the key design parameters in determining structural performance under elevated temperatures.