Fire Resistance of Floors Constructed with Fire-Resistant Steels

Abstract

Fire resistance of floor structures using steel sections has been modeled using bending-moment resistance calculations based on temperature data measured in fire tests. Three types of floors are investigated: (1) conventional composite floor using protected I-beam; (2) noncomposite SLIMFLOR; and (3) composite SLIMDEK asymmetric beam slim floor systems. The effect on construction using fire-resistant steels is investigated; the steels under consideration having a strength reduction factor of around 0.5 at 700°C, an increase of some 100°C compared with conventional structural steels. It has been found that the improvement in fire resistance is limited, especially in the case of slim floor systems where there is already efficiently built-in fire resistance. The fire resistance is increased by 22–24 min by using the fire-resistant steels for the I-beam floor, whereas such improvement is only 11–16 min in the case of slim floor constructions. To achieve a 30-min increase in fire resistance in the I-beam floor structure, the strength reduction factor curve of the steel needs to shift by 150°C to higher temperatures.