FIRE RESISTANCE OF FLOORS CONSTRUCTED WITH FIRE-RESISTANT STEELS

Fire resistance of floor structures using steel sections has been mode led 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) noncomposi te SLIMFLOR; and (3) composite SLIMDEK asymmetric beam slim floor syst ems. The effect on construction using fire-resistant steels is investi gated; the steels under consideration having a strength reduction fact or of around 0.5 at 700 degrees C, an increase of some 100 degrees C c ompared with conventional structural steels. It has been found that th e improvement in fire resistance is limited, especially in the case of slim floor systems where there is already efficiently built-in fire r esistance. The fire resistance is increased by 22-24 min by using the fire-resistant steels for the I-beam floor, whereas such improvement i s 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 de grees C to higher temperatures.