Composite steel and concrete fl ooring, as used today, was developed in the 1960s to economically increase the spans of steel framed fl oors while minimizing the required structural depths.

Concrete slab There are various types of slab: solid in situ, in situ on profi led metal deck and in situ on precast concrete units. Solid slabs are typically 125-150 mm thick and require formwork. The precast and metal deck systems both act as permanent formwork, which may need propping to control defl ections. The profi led metal deck sheets have a 50-60 mm depth to create a 115-175 mm slab, which can span 2.5 to 3.6 m. Precast concrete units 75-100 mm thick with 50-200 mm topping can span 3-8 m.