DESPACHOS DE LOS MÓDULOS

7.1.2 Definitions 7.1.2.1 Composite slab

A composite slab is one in which profiled steel sheets are used as permanent shuttering capable of supporting the wet concrete, reinforcement and construction loads. Subsequently, the profiled steel sheets combine structurally with the hardened concrete and act as part or all of the tensile reinforcement in the finished floor.

7.1.2.2 Composite behaviour

Composite behaviour is that which occurs after a floor slab comprising profiled steel sheet, plus any additional reinforcement, and hardened concrete have combined to form a single structural element. The profiled steel sheet shall be capable of transmitting horizontal shear at the interface between the sheet and the concrete; pure bond between steel sheeting and concrete is not considered effective for composite action.

Composite behaviour between profiled sheeting and concrete shall be ensured by one or more of the following means (see Figure 7.1):

a) mechanical interlock provided by deformations in the profile (indentations or embossments);

b) frictional interlock for profiles shaped in a re-entrant form;

c) end anchorage provided by welded studs or another type of local connection between the concrete and the steel sheet, only in combination with a) or b);

d) end anchorage by deformation of the ribs at the end of the sheeting, only in combination with b).

Other means are not excluded but are not within the scope of this Eurocode.

7.2 Detailing provisions

7.2.1 Slab thickness and reinforcement

1) The overall depth of the composite slab h shall be not less than 80 mm. The thickness of concrete, h_c, above the main flat surface of the top of the ribs of the sheeting shall be not less than 40 mm.

2) If the slab is acting compositely with the beam or is used as a diaphragm, the total depth shall be not less than 90 mm and h_c shall be not less than 50 mm.

3) Where reinforcement is required to be placed within the depth h_c of the concrete, the maximum spacing of the bars should be in accordance with clause 5.4.3.2.1 of EC2, based on the overall depth h of the composite slab, unless closer spacing is required for the control of cracking (Section 5.3).

7.2.2 Aggregate

The nominal size of the aggregate depends on the smallest dimension in the structural element within which concrete is poured, and shall not exceed the least of:

a) 0.40 h_c (see Figure 7.2);

b) b_o/3, where b_o is the mean width of the ribs (minimum width for re-entrant profiles) (see Figure 7.2);

c) 31.5 mm (sieve C 31.5).

7.2.3 Bearing requirements

1) Bearing at temporary supports of profiled steel sheeting as shuttering shall be checked in accordance with Part 1.3 of Eurocode 3.

2) Composite slabs bearing on steel or concrete should have a minimum bearing of 75 mm with a minimum end bearing of 50 mm for the profiled steel sheeting [see Figure 7.3(a) and Figure 7.3(c)].

3) For composite slabs bearing on other materials these values should be increased to a minimum of 100 mm and 70 mm respectively [see Figure 7.3(b) and Figure 7.3(d)].

Figure 7.1 — Typical forms of interlock in composite slabs

Figure 7.2 — Sheet and slab dimensions

4) For overlapping and continuous sheets bearing on steel or concrete, the minimum bearing should be 75 mm and for other materials 100 mm [see Figure 7.3(e) and Figure 7.3(f)].

5) The minimum bearings given above may be reduced, if speckled in the project specifications and provided the design takes into account relevant factors such as tolerances, loading, span, height of support and provision of continuity reinforcement. When reduced bearings are used, precautions should be taken that fastening of the sheet can still be achieved without damage to the bearings, and that collapse cannot occur as a result of accidental displacement during erection.

7.3 Actions and action effects

7.3.1 Design situations

All relevant design situations and limit states shall be considered in design so as to ensure an adequate degree of safety and serviceability. The following situations are considered in this code.

i) Profiled steel sheeting as shuttering

Verification is required for the behaviour of the profiled steel sheeting while it is acting as formwork for the wet concrete. Account shall be taken of the effect of props, if any.

ii) Composite slab

Verification is required for the floor slab after composite behaviour has commenced and any props have been removed.

7.3.2 Actions

7.3.2.1 Profiled steel sheet as shuttering

1) The following loads shall be taken into account in calculation for the steel deck as shuttering:

— weight of concrete and steel deck;

— construction loads including local heaping of concrete during construction;

— storage load, if any;

— “ponding” effect (increased depth of concrete due to deflection of the sheeting).

[Note: Until sufficient information is given in Eurocode 1, the following rules apply.]

Figure 7.3 — Minimum bearing lengths

2) The construction loads represent the weight of operatives and concreting plant and take into account any impact or vibration which may occur during construction. In any area of 3 m by 3 m (or the span length, if less), in addition to the weight of the concrete, the characteristic construction load and weight of surplus concrete should together be taken as 1.5 kN/m². Over the remaining area a characteristic loading

of 0.75 kN/m² should be added to the weight of concrete. These loads should be placed to cause the maximum bending moment and/or shear.

3) These minimum values are not necessarily sufficient for excessive impact or heaping of concrete, or pipeline or pumping loads. If appropriate, provision should be made in design for the additional loading.

Without the concrete the sheet should be shown by test or calculation to be able to resist a characteristic load of 1 kN on a square area of side 300 mm, in the most unfavourable place, at any location except a rib adjacent to a free edge.

4) If the central deflection $ of the sheeting under its own weight plus that of the wet concrete, calculated for serviceability, is less than =/250 and less than 20 mm, the ponding effect may be ignored in the design of the steel sheeting. If either of these limits is exceeded, this effect should be allowed for; for example by assuming in design that the nominal thickness of the concrete is increased over the whole span by 0.7$.

7.3.2.2 Composite slab

In design checks for the ultimate limit state it may be assumed that the whole of the loading acts on the composite slab, provided this assumption is also made in design for longitudinal shear.

7.3.3 Load combinations load cases

1) The loads shall be applied in whatever realistic combination is most unfavourable for the effect under consideration