BS Standard for composite slabs with profiled steel 5

Design: profiled steel sheeting

General

The design of profiled steel sheeting supporting loads before composite action is eveloped should follow the recommendations given in this section. The recommendations given in BS 5950-66) should be followed for the calculation of cross-sectional properties. Alternatively the load-carrying capacity of the profiled steel sheeting should be determined by testing (see 5.2). Embossments and indentations designed to provide composite action should be ignored when calculating the cross-sectional properties of the steel sheets.

NOTE : The cross-sectional properties of commercially available profiles can be found in manufacturers’ literature, together with information on effective cross-sectional properties at various stress levels.

Load carrying capacity

For design purposes, the loads carried by the profiled steel sheeting should be the dead load of the sheets, wet concrete and reinforcement, the construction loads (see 2.2.3), the effects of any temporary propping used at this stage and, where necessary, wind forces.

For simple spans, the capacity of the profiled steel sheeting should be determined as recommended in BS 5950-66) by either:

a) calculation; or

b) testing.

For sheets continuous over more than one span, the capacity should be determined either by using one of the methods recommended for simple spans or from a hybrid design method, based on elastic section properties supplemented by information obtained by testing.

NOTE An appropriate hybrid design method is given in CIRIA Technical Note 116[1].

Deflection of profiled steel sheeting

The deflections of profiled steel sheeting should be calculated as recommended in BS 5950-66) using the serviceability loads (see 2.5.1) for the construction stage, comprising the weight of the profiled sheets and the wet concrete only. These deflections should not normally exceed the following:

a) Lp /180 (but # 20 mm) when the effects of ponding are not taken into account;

b) Lp /130 (but # 30mm) when the effects of ponding are taken into account, i.e. the weight of additional concrete due to the deflection of the sheeting is included in the deflection calculation;

where Lp is the effective span of the profiled steel sheets. These limits should be increased only where it can be shown that greater deflections will not impair the strength or efficiency of the slab.

These limits should be reduced, if necessary, where soffit deflection is considered important, e.g. for service requirements or aesthetics. When the deflection [calculated as in item a] exceeds Ds /10, where Ds is the overall depth of the composite slab, the additional weight of concrete due to the deflection of the sheeting should be taken into account in the self-weight of the composite slab, for use in section 6 and in the design of the supporting structure.