Flexure
The design procedure for flexural design is given in Figure 1; this includes derived formulae based on the simplified rectangular stress block from Eurocode 2. Where appropriate Table 3 may be used to determine bending moments for flat slabs.
Table 1
Flat slab design procedure
Step 
Task 
Further guidance  
Chapter in this publication 
Standard  
1 
Determine design life 
2: Getting started 
NA to BS EN 1990 Table NA.2.1 
2 
Assess actions on the slab 
2: Getting started 
BS EN 1991 (10 parts) and National Annexes 
3 
Determine which combinations of actions apply 
1: Introduction to Eurocodes 
NA to BS EN 1990 Tables NA.A1.1 and NA.A1.2 (B) 
4 
Determine loading arrangements 
2: Getting started 
NA to BS EN 199211 
5 
Assess durability requirements and determine concrete strength 
2: Getting started 
BS 8500: 2002 
6 
Check cover requirements for appropriate fire resistance period 
2: Getting started and Table 2 
Approved Document B. BS EN 199211: Section 5 
7 
Calculate min. cover for durability, fire and bond requirements 
2: Getting started 
BS EN 199211 Cl 4.4.1 
8 
Analyse structure to obtain critical moments and shear forces 
2: Getting started and Table 3 
BS EN 199211 Section 5 
9 
Design flexural reinforcement 
See Figure 1 
BS EN 199211 Section 6.1 
10 
Check deflection 
See Figure 3 
BS EN 199211 Section 7.4 
11 
Check punching shear capacity 
See Figure 6 
BS EN 199211 Section 6.4 
12 
Check spacing of bars 
2: Getting started 
BS EN 199211 Section 7.3 
13 
Check resistance to moment transfer from column to slab 
 
BS EN 199211 Annex I 1.2(5) 
Note NA = National Annex 
Table 2
Minimum dimensions and axis distances for reinforced concrete slabs
Standard fire resistance 
Minimum dimensions (mm)  
Slab thickness, hs 
Axis distance, a  
REI 60 
180 
15a  
REI 90 
200 
25  
REI 120 
200 
35  
200 
50  
Notes  
1 This table is taken from BS EN 199212 Table 5.9.  
2 The axis distance is to the centre of the outer layer of reinforcement.  
3 The table is valid only if the detailing requirements (see note 4) are observed and, in the normal temperature design, redistribution of bending moments does not exceed 15%.  
4 For fire resistance of R90 and above, at least 20% of the total top reinforcement in each direction over intermediate supports required by BS EN 199211 should be continuous over the full span. This reinforcement should be placed in the column strip.  
5 There are three standard fire exposure conditions that may 
need to be satisfied:  
R Mechanical resistance for load bearing E Integrity of separation I Insulation Key  
a Normally the requirements of BS EN 199211 will determine the cover. 
Procedure for determining flexural reinforcement START Carry out analysis of slab to determine design moments (M) (Where appropriate use coefficients from Table 3). Carry out analysis of slab to determine design moments (M) (Where appropriate use coefficients from Table 3).
Compression reinforcement required  not recommended for typical slabs Obtain lever arm z from Table 5 or Compression reinforcement required  not recommended for typical slabs Obtain lever arm z from Table 5 or z = d [ 1 + V1  3 53 K ] < 0.95d z = d [ 1 + V1  3 53 K ] < 0.95d 
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