Engineering and Construction

Universal beams supporting precast prestressed floor units (Fig. 2.28) have some advantages over other forms of construction. Although of heavier construction  than comparable composite metal deck floors, this system offers the following advantages.

• Fewer floor beams since precast floor units can span up to 6–8m without  difficulty.
• No propping is required.
• Shallow floor construction can be obtained by supporting precast floor units on shelf angles or on wide plates attached to the bottom flanges of universal columns acting as beams (Slimfloor).
• Fast construction because no time is needed for curing and the development of concrete strength.

On the other hand the disadvantages are:

• Composite and diaphragm action is not readily achieved without  a structural floor screed.
• Heavy floor units are difficult to erect in many locations and require the use of a tower crane, which may have implications for the construction programme.

Fig. 2.28 Precast concrete floors