The load arrangements given in 2.2.5 5) should be considered

7.4 Analysis for internal forces and moments

7.4.1 Profiled steel sheeting as shuttering

1) Elastic analysis shall be used. Where sheeting is considered as continuous, flexural stiffness may be determined without consideration of the variation of stiffness due to parts of the cross-section in compression not being fully effective.

2) Where shuttering is assumed to provide lateral bracing, the appropriate rules in Part 1.3 of Eurocode 3 apply, it may be assumed that the effectiveness of the lateral restraint is not impaired when the shuttering carries wet concrete.

7.4.2 Composite slab 7.4.2.1 Analysis

1) The following methods of analysis may be used:

a) linear analysis with or without redistribution;

b) rigid-plastic global analysis based either on the kinematic method (upper bound) or on the static method (lower bound) provided that it is shown that sections where plastic rotations are required have sufficient rotation capacity;,

c) elastic-plastic analysis taking into account the non-linear material properties.

2) The application of linear methods of analysis is suitable for the serviceability limit states as well as for the ultimate limit states. Plastic methods, with their high degree of simplification, shall only be used in the ultimate limit state.

Figure 7.4 — Loads on profiled sheeting

3) If the effects of cracking of concrete are neglected in the analysis, the bending moments at internal supports may optionally be reduced by up to 30 %, and corresponding increases made to the sagging bending moments in the adjacent spans.

4) A continuous slab may be designed as a series of simply supported spans. Nominal reinforcement in accordance with 7.6.2.1 should be provided over intermediate supports.

5) Plastic analysis without any direct check on rotation capacity may be used for the ultimate limit state if reinforcing steel of class H in accordance with clause 3.2.2 of EC2 is used and the span is less than 3.0 m.

7.4.2.2 Effective width for concentrated point and line loads

1) Where concentrated point or line loads parallel to the span of the slab are to be supported by the slab, they may be considered to be distributed over a width b_m, measured immediately above the ribs of the sheeting, as shown in Figure 7.5 and given by:

2) For concentrated line loads perpendicular to the span of the slab, the preceding formula for b_m may be used, with b_p taken as the length of the concentrated line load.

3) The width of the slab considered to be effective for global analysis and for resistance should not exceed the following:

a) for bending and longitudinal shear:

— for simple spans and exterior spans of continuous slabs

— for interior spans of continuous slabs

b) for vertical shear:

4) To ensure the distribution of line or point loads over the width considered to be effective, transverse reinforcement shall be placed on or above the sheeting. This transverse reinforcement shall be designed in accordance with Eurocode 2 for the transverse bending moments.

b_m = b_p+ 2(h_c+ h_f) (7.1)

where: b_p is the width of the concentrated load, perpendicular to the span of the slab;

h_c is the thickness of the slab above the ribs of the profiled sheeting and h_f is the thickness of the finishes, if any.

Figure 7.5 — Distribution of concentrated load

b_em = b_m+ 2L_p[1 – (L_p/L)] k slab width (7.2)

b_em = b_m+ 1.33 L_p[1 – (L_p/L)] k slab width (7.3)

b_eÉ = b_m+ L_p [1 – (L_p/L)] k slab width (7.4)

where: L_p is the distance from the centre of the load to the nearest support;

L is the span length.

5) If the characteristic imposed loads do not exceed the following values, a nominal transverse reinforcement may be used without calculation:

— concentrated load: 7.5 kN

— distributed load: 5.0 kN/m².

This nominal transverse reinforcement should have a cross-sectional area of not less than 0.2 % of the area of structural concrete above the ribs, and should extend over a width of not less than b_em as calculated in this clause. Minimum anchorage lengths should be provided beyond this width in accordance with clause 5.2.3.4 of EC2. Reinforcement provided for other purposes may fulfil all or part of this rule.

6) In the absence of such reinforcement, effective widths for both shear and moment calculations are limited to b_m.

7.5 Verification of profiled steel sheeting as shuttering

7.5.1 Ultimate limit state

Verification of the profiled steel sheeting for the ultimate limit state shall be in accordance with Part 1.3 of Eurocode 3. Due consideration shall be given to the effect of embossments or indentations on the design resistances.

7.5.2 Serviceability limit state

1) Section properties shall be determined in accordance with Part 1.3 of Eurocode 3.

2) The deflection of the sheeting under its own weight plus the weight of wet concrete, but excluding the construction load, should not exceed

L/180 or 20 mm

where L is the effective span between supports (props being supports in this context).

3) These limits may be varied where:

— greater detection will not impair the strength or efficiency of the floor; and

— the additional weight of concrete due to ponding is taken into account in the design of the floor and supporting structure.

4) Where soffit deflection is considered important (e.g. for service requirements or aesthetics) it may be necessary to reduce these limits.

7.6 Verification of composite slabs

7.6.1 Ultimate limit state 7.6.1.1 Design criteria

1) The resistance of a composite slab shall be sufficient to withstand the design loads and to ensure that no ultimate limit state is reached, based on one of the following modes of failure (see Figure 7.6):

— Critical section I.

Flexure: bending resistance M_p.Rd.

This section can be critical if there is complete shear connection at the interface between the sheet and the concrete (see 7.6.1.2).

— Critical section II.

Longitudinal shear: longitudinal shear resistance V_=.Rd.

The maximum load on the slab is determined by the resistance of the shear connection. The ultimate moment of resistance M_p.Rd at section I cannot be reached. This is defined as partial shear connection (see 7.6.1.3).

— Critical section III.

Vertical and punching shear: vertical shear resistance V_v.Rd.

This section will be critical only in special cases, for example in deep slabs of short span with loads of relatively large magnitude (see 7.6.1.5).

7.6.1.2 Flexure

1) The bending resistance M_p.Rd of any cross section shall be determined by plastic theory in accordance with 4.4.1.2 but with the design yield strength of the steel member (sheeting) taken as f_yp/*_ap.

In hogging bending the contribution of the steel sheeting shall only be taken into account when the sheet is continuous.

2) For the effective area of the steel sheeting the width of embossments and indentations in the sheet should be neglected, unless it is shown by tests that a larger area is effective.

3) The effect of local buckling of compressed parts of the sheeting should be taken into account by using effective widths not exceeding twice the values given in Table 4.2 for Class I steel webs.

4) The sagging bending resistance of a composite slab with the neutral axis above the sheeting may be calculated as follows:

The stress distribution is given in Figure 7.7.

Figure 7.6 — Illustration of possible critical sections

M_p.Rd= N_cf (d_p– 0.5 x) (7.5a)

where N_cf is A_p f_yp/*ap;

A_p is the effective area of the steel sheet in tension according to paragraph 2);

d_p is the distance from the top of the slab to the centroid of the effective area of the steel sheet;

x is the depth of the stress block for the concrete, given by

b is the width of the cross-section considered.

Figure 7.7 — Stress distribution for sagging bending if the neutral axis is above the steel sheet

5) The sagging bending resistance of a composite slab with the neutral axis in the sheeting may be calculated from Figure 7.8 or for simplification as follows (concrete in the ribs neglected):

and other symbols are as in 4) above.

7.6.1.3 Longitudinal shear for slabs without end anchorage

1) The provisions in this clause 7.6.1.3 apply to composite slabs with mechanical or frictional interlock