Slabs - Deck types

Deck profiles are usually in the range of 38–80mm height and 150–300mm trough spacing with sheet thicknesses between 0.8mm and 1.5mm, use of the lower thickness being limited by local buckling and the upper thickness by difficulties in rolling.

A summary of the different decking profiles marketed for use in composite slabs is shown in Fig. 20.2. There are two well-known generic types: the dovetail profile and the trapezoidal profile with web indentations.

Fig. 20.2 Examples of modern composite deck profiles

The shape of the profile is controlled by a number of criteria:

(1) the need to maximize the efficiency of the cross-section in bending (both positive and negative moments)

(2) the need to develop adequate composite action with the concrete by use of embossments or indentations or by the shape of the profile itself

(3) the efficient transfer of shear from the beam into the concrete slab (a similar problem to the haunch design in reinforced concrete slabs).

Practice in North America has been to use profiles with a trough pitch typically  300mm and 50mm height to achieve a 3m span without temporary propping.

In the UK, spans of 3.5–3.75m are achieved with profiles of typically 60mm depth.

Slimflor ® construction2 has also led to the development of deep deck profiles of 210–225mm depth and 1.0–1.25mm thickness. The total slab depth of 280–310mm is such that the steel beam is fully encased in the slab except for its bottom flange.

The deep deck slab is designed for spans of 6m when unpropped during construction, or up to 7.5m when propped. The beam may take the form of a universal column section with a welded plate or three welded plates. Recent developments by Corus have resulted in the rolling of asymmetric beams.

These are rolled with a patterned top flange which enhances the composite action between the beam and
the overlying in situ concrete thus eliminating the need for welded shear connectors. The rolled sections have webs of greater thickness than that of the flanges to achieve superior fire resistance properties, and this extra web thickness also enhances the torsional properties of the section.

The grades of steel used for decking are specified in BS EN 10147. The common grades in the UK are S280 and S350. Steel decking is usually galvanized to a standard of 275 g/m2 (roughly 0.04mm per face), which gives adequate protection for internal use.

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