Table

Bending moment coefficients for flat slabs

End support/slab connection First Interior Interior

-- interior spans supports

Pinned Continuous support

End End End End support span support span

Moment 0

G.GB6FI -G.G4FI G.G7SFI -G.GB6FI G.G63FI

G.G6SFl

Notes

1 Applicable to slabs where the area of each bay exceeds 30 m2, Qk, < 1.25 Gk and qk < 5 kN/m2

2 F is the total design ultimate load, l is the effective span

3 Minimum span > 0.85 longest span, minimum 3 spans

4 Based on 20% redistribution at supports and no decrease in span moments

Whichever method of analysis is used, CI. 9.4.1 requires the designer to concentrate the reinforcement over the columns. Annex I of the Eurocode gives recommendations for the equivalent frame method on how to apportion the total bending moment across a bay width into column and middle strips to comply with CI. 9.4.1. Designers using grillage, finite element or yield line methods may also choose to follow the advice in Annex I to meet this requirement.

Eurocode 2 offers various methods for determining the stress-strain relationship of concrete. For simplicity and familiarity the method presented here is the simplified rectangular stress block (see Figure 2), which is similar to that found in BS 8110.

The Eurocode gives recommendations for the design of concrete up to class C90/105. However, for concrete strength greater than class C50/60, the stress block is modified. It is important to note that concrete strength is based on the cylinder strength and not the cube strength (i.e. for class C28/35 the cylinder strength is 28 MPa, whereas the cube strength is 35 MPa).

Table 4 Values for K'

% redistribution

1 6 (redistribu

tion ratio) | K'

G

1.GG

G.2GBa

1G

G.9G

G.182a

15

G.BS

G.16B

2G

G.BG

G.1 S3

25

G.7S

G.137

3G

G.7G

G.12G

Key a It is often recommended in the UK that K should be Uimited to 0.168 to ensure ductile failure

Table 5

z/d for singly reinforced rectangular sections

Table 5

z/d for singly reinforced rectangular sections

K

1 z/d

■ K

\z/d

s G.GS

G.9SGa

G.13

G.B6B

G.G6

G.944

1 |G.14

G.BS6

G.G7

G.934

G.1 S

G.B43

G.GB

G.924

G.16

G.B3G

G.G9

G.913

1 (G.17

G.B16

G.1G

G.9G2

G.18

G.BG2

G.11

G.B91

1 (G.19

G.7B7

G.12

G.BBG

G.2G

G.771

Key a Limiting z to 0.95d is not a requirement of Eurocode 2, but is considered to be good practice

Table 6

Minimum percentage of reinforcement required

Table 6

Minimum percentage of reinforcement required

fck

l/ctm

1 Minimum % (0.26 fctm /fyka )

25

2.6

G.13%

28

2.8

G.14%

30

2.9

G.1 S%

32

3.G

G.16%

35

3.2

G.17%

40

3.S

G.18%

45

3.8

G.2G%

50

4.1

G.21%

Key a Where fyk =

SGG MPa

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Responses

  • CRYSTAL
    What eurocode design is based on cylinder strength and not cube strength?
    3 years ago

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