Steel Buildings in Europe

Part 6: Fire Engineering 6 - 20 As an alternative to precast concrete floors, composite floors, shown in Figure 3.7(b), are popular in multi-storey buildings. (a) (b) Figure 3.7 (a) Precast concrete floor on down stand beam; (b) composite floors with steel decking Composite floors are constructed using either trapezoidal or re-entrant profiled steel decking that supports the concrete on top. In a composite floor, the concrete is reinforced using fibre or bar reinforcement to control cracks caused by the flexural tension at the floor support, and by shrinkage and settlement of the concrete. In addition to controlling cracks, the bar reinforcement also provides the floor with bending resistance at its support in the fire condition. For a composite floor with the bottom surface exposed, the insulation criterion is usually satisfied by providing sufficient insulation depth of the concrete for the required fire resistance period, as shown in Table 3.4. The longer the required fire resistance period, the thicker the insulation concrete needs to be. The integrity criterion is generally met by using continuous steel decking. Table 3.4 Typical minimum insulation thickness (mm), h 1 , of concrete in composite floors Trapezoidal steel decking Re-entrant steel decking Required Fire Resistance (minutes) Normal weight concrete Light weight concrete Normal weight concrete Light weight concrete 60 70 60 90 90 90 80 70 110 105 120 90 80 125 115 Table 3.5 shows typical depths and spans of composite floors with normal weight concrete under a uniform applied load of 5,0 kN/mm 2 . h 1 h 2 h 2 h 1