BS for composite slabs with profiled steel sheeting 1

Materials

1.    profiled steel sheets

a.    Specification 

The steel used to manufacture the profiled steel sheets should have a specified yield strength Re.min of not less than 220 N/mm2 and should generally be in accordance either with BS 2989:1992 or with BS EN 10147:1992. Steels conforming to other specifications may alternatively be used provided that they have similar properties.

b.   Sheet thickness

The structural thickness of the profiled steel sheets, to which the stresses and section properties apply, should be taken as the “bare metal thickness” of the sheets excluding any protective or decorative finish such as zinc coating or organic coating. The nominal bare metal thickness of the sheets should not normally be less than 0.75 mm except where the profiled steel sheets are used only as permanent shuttering (see 4.1). Thinner sheets should not be used unless adequate theoretical evidence and test data are available to justify their use.

c.    Zinc coating

The zinc coating should conform to the requirements of BS 2989:1992 or BS EN 10147:1992 as appropriate. A coating of 275 g/m2 total, including both sides (coating type G 275 in accordance with BS 2989) is normally specified for internal floors in a non-aggressive environment, but the specification may be varied depending on service conditions.

NOTE A 275 g/m² coating adds approximately 0.04 mm to the bare metal thickness, 0.02 mm on each side. The nominal bare metal thickness is thus 0.04 mm less than the nominal thickness of the sheet.

Before a zinc coating heavier than 275 g/m² is specified, confirmation should be obtained from the proposed manufacturer of the profiled steel sheets that the proposed coating thickness is compatible with the forming operations involved. All zinc coatings should be chemically passivated with a chromate treatment to inimize wet storage stains (white rusting) and reduce chemical reaction at the concrete/zinc interface.

2.   Steel reinforcement

a.    Specification

The type of reinforcement used should satisfy the recommendations of BS 8110 and should conform to BS 4449:1988, BS 4482:1985 or BS 4483:1985, subject to the recommendations in

b.    Ductility of reinforcement

Wherever account is taken in design of the efficiency of continuity over a support, to ensure that the reinforcement has adequate ductility the steel fabric or reinforcing bars used as support reinforcement should satisfy the minimum elongation requirement specified in 10.1.2 of BS 4449:1988.

This recommendation should be applied to the following:

a) reinforcement used to resist negative moments in continuous spans or cantilevers;

b) distribution steel for concentrated loads or around openings in the slab;

c) reinforcement used to increase the fire resistance of the composite slab.

However it need not be applied to the following:

1) secondary transverse reinforcement;

2) nominal continuity reinforcement over supports;

3) tensile reinforcement in the span.