Table

Bending moment and shear coefficients for slabs

End support/slab connection

Pinned Continuous

End End End End support span support span

First Interior Interior interior spans supports support

Moment O O.O86F/ -O.O4F/ O.O7SF/ -O.O86F/ O.O6SFI -O.O6SF/

Notes

1 Applicable to one-way spanning slabs where the area of each bay exceeds 30 m2, Qk < 1.25 Ck and qk<5 kN/m2

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

3 Minimum span > 0.85 longest span, minimum 3 spans

4 Based on 20% redistribution at supports and no decrease in span moments dimension, so the designer should ensure that a — ^nom + f Link + f bar / 2.

The requirements for various types of slab are given in Table 2.

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 and shear forces for slabs. Further information for the design of two-way, ribbed or waffle slabs is given in the appropriate sections on pages 5 and 6.

Table 4 Values for K '

% redistribution

1 d (redistribution ratio)

K'

O

l.OO

O.2O8a

1O

O.9O

O.l 82a

1S

O.8S

O.168

2O

O.8O

O.l SS

2S

O.7S

O.1S7

SO

O.7O

O.12O

Key a It is often recomended in the UK that K should be limited 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

<O.OS

O.9SOa

O.1S O.868

O.O6

O.944

O.14 O.8S6

O.O7

O.9S4

O.1S O.84S

O.O8

O.924

O.l 6 O.8SO

O.O9

O.91 S

O.l 7 O.816

O.1O

O.9O2

O.l 8 O.8O2

O.ll

O.891

O.l 9 O.787

O.l 2

O.88O

O.2O O.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

fck

1 fctm

1 Minimum% (0.26fctm/fyka )

25

2.6

O.m

28

2.8

1 O.14%

30

2.9

1 O.1S%

32

1 S.O

1 O.16%

35

S.2

1 O.l 7%

40

S.S

1 O.18%

45

S.8

1 O.2O%

50

1 4.1

1 O.21%

Key a Where fyk

= SOO MPa.

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, which is similar to that found in BS 8110 (see Figure 2).

The Eurocode gives recommendations for the design of concrete up to class C90/105. However, for concrete 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).

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