Fragility curves for structural fire performance of various composite floor designs under natural fire

Although structural fire design in the United States is primarily prescriptive, performance-based approaches are increasingly considered for their potential to deliver flexible, resilient, and economic solutions. However, comparisons of performance between designs resulting from the two approaches have rarely been performed, especially under natural fires and considering uncertainty in demand and response. To support a comparative assessment of the value delivered by prescriptive and performance-based designs, this study conducts a probabilistic numerical analysis of steel-concrete composite floors under natural fires including the cooling phase. Fragility curves are developed for various floor designs to quantify for each the probability of damage states as a function of the fire severity. Results show that the performance-based design using tensile membrane action has a higher probability of moderate damage but a lower probability of integrity failure than the prescriptive design. Parametric analyses show that increasing the amount of slab reinforcement or the amount of axial restraint at the boundaries further reduces the probability of failure. This work contributes to developing a database of fire fragility functions for evaluating the probabilistic performance of various fire designs. These findings can support fire loss analyses and comparative assessment of the impact of adopting a performance-based structural fire design.