17. Slab Design

A. Design of One-Way Slabs

La = length of short side

Lb = length of long side

La

Lb0.5 : the slab in one-way

La

Lb0.5 : the slab is two-way

Thickness of one-way slab

Simply supportedLn

20

One end continuousLn

24

Both ends continuousLn

28

CantileverLn

10

Analysis of one-way slab

Design scheme: continuous beam

Determination of bending moments: using ACI moment coefficients

Design of one-way slab

Design section: rectangular section of 1m x h

Type section: singly reinforced beam

Page 115

Example 17.1

Span of slab Ln 2m 20cm 1.8 m

Live load LL 12kN

m2

Materials f'c 20MPa

fy 390MPa

Solution

Thickness of one-way slab

tmin

Ln

2864.286 mm

Use t 100mm

Loads on slab

Cover 50mm 22kN

m3

1.1kN

m2

Slab t 25kN

m3

2.5kN

m2

Ceiling 0.40kN

m2

Mechanical 0.20kN

m2

Partition 1.00kN

m2

DL Cover Slab Ceiling Mechanical Partition 5.2kN

m2

wu 1.2 DL 1.6 LL 25.44kN

m2

Bending moments

Msupport1

11wu Ln

2 7.493

kN m

1m

Mmidspan1

16wu Ln

2 5.152

kN m

1m

Steel reinforcements

Page 116

β1 0.65 max 0.85 0.05f'c 27.6MPa

6.9MPa

min 0.85

0.85

εu 0.003

ρmax 0.85 β1f'c

fy

εu

εu 0.005 0.014

ρmin max

0.249MPaf'c

MPa

fy

1.379MPa

fy

0.00354

ρshrinkage 0.0020return( ) fy 50ksiif

0.0018return( ) fy 60ksiif

max 0.001860ksi

fy 0.0014

return

otherwise

ρshrinkage 0.0018

Top rebars

b 1m d t 20mm10mm

2

75 mm

Mu Msupport b 7.493 kN m

Mn

Mu

0.98.326 kN m

RMn

b d2

1.48 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.004 ρ ρmax 1

As max ρ b d ρshrinkage b t 2.982 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 3 t 450mm( )

s min Floorb

n10mm

smax

260 mm

Bottom rebars

Mu Mmidspan b 5.152 kN m

Mn

Mu

0.95.724 kN m

Page 117

RMn

b d2

1.018 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.003 ρ ρmax 1

As max ρ b d ρshrinkage b t 2.019 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 3 t 450mm( )

s min Floorb

n10mm

smax

300 mm

Link rebars

As ρshrinkage b t 1.8 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 5 t 450mm( )

s min Floorb

n10mm

smax

430 mm

B. Design of Two-Way Slabs

Design methods:- Load distribution method- Moment coefficient method- Direct design method (DDM)- Equivalent frame method- Strip method- Yield line method

Page 118

(1) Load Distribution Method

Principle: Equality of deflection in short and long directions

fa fb=

αa

wa La4

EI αb

wb Lb4

EI=

Case αa αb=

wa

wb

Lb4

La4

=1

λ4

= λLa

Lb=

wa wb wu=

From which, wa wu1

1 λ4

=

wb wuλ

4

1 λ4

=

For λ 11

1 λ4

0.5

λ4

1 λ4

0.5

For λ 0.81

1 λ4

0.709

λ4

1 λ4

0.291

For λ 0.61

1 λ4

0.885

λ4

1 λ4

0.115

For λ 0.51

1 λ4

0.941

λ4

1 λ4

0.059

For λ 0.41

1 λ4

0.975

λ4

1 λ4

0.025

Page 119

Example 17.2

Slab dimension La 4.3m

Lb 5.5m

Live load LL 2.00kN

m2

Materials f'c 20MPa

fy 390MPa

Solution

Thickness of two-way slab

Perimeter La Lb 2

tminPerimeter

180108.889 mm

t1

30

1

50

La 143.333 86( ) mm

Use t 120mm

Loads on slab

SDL 50mm 22kN

m3

0.40kN

m2

1.00kN

m2

2.5kN

m2

DL SDL t 25kN

m3

5.5kN

m2

LL 2kN

m2

wu 1.2 DL 1.6 LL 9.8kN

m2

Load distribution

λLa

Lb0.782

wa1

1 λ4

wu 7.134

kN

m2

wbλ

4

1 λ4

wu 2.666

kN

m2

Page 120

Bending moments

Ma.neg1

11wa La

2 11.992

kN m

1m

Ma.pos1

16wa La

2 8.245

kN m

1m

Mb.neg1

11wb Lb

2 7.33

kN m

1m

Mb.pos1

16wb Lb

2 5.04

kN m

1m

Steel reinforcements

β1 0.65 max 0.85 0.05f'c 27.6MPa

6.9MPa

min 0.85

0.85

εu 0.003

ρmax 0.85 β1f'c

fy

εu

εu 0.005 0.014

ρmin max

0.249MPaf'c

MPa

fy

1.379MPa

fy

0.00354

ρshrinkage 0.0020return( ) fy 50ksiif

0.0018return( ) fy 60ksiif

max 0.001860ksi

fy 0.0014

return

otherwise

ρshrinkage 0.0018

Top rebar in short direction

b 1m d t 20mm 10mm10mm

2

85 mm

Mu Ma.neg b 11.992 kN m

Mn

Mu

0.913.325 kN m

RMn

b d2

1.844 MPa

Page 121

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.005 ρ ρmax 1

As max ρ b d ρshrinkage b t 4.265 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

180 mm

Bottom rebar in short direction

Mu Ma.pos b 8.245 kN m

Mn

Mu

0.99.161 kN m

RMn

b d2

1.268 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.003 ρ ρmax 1

As max ρ b d ρshrinkage b t 2.875 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

Top rebar in long direction

Mu Mb.neg b 7.33 kN m

Mn

Mu

0.98.145 kN m

RMn

b d2

1.127 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.003 ρ ρmax 1

As max ρ b d ρshrinkage b t 2.544 cm2

Page 122

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

Bottom rebar in long direction

Mu Mb.pos b 5.04 kN m

Mn

Mu

0.95.599 kN m

RMn

b d2

0.775 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.002 ρ ρmax 1

As max ρ b d ρshrinkage b t 2.16 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

Shrinkage rebars

b 1m

As ρshrinkage b t 2.16 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 5 t 450mm( )

s min Floorb

n10mm

smax

360 mm

Page 123

(2) Moment Coefficient Method

Negative moments

Ma.neg Ca.neg wu La2

=

Mb.neg Cb.neg wu Lb2

=

Positive moments

Ma.pos Ca.pos.DL wD La2

Ca.pos.LL wL La2

=

Mb.pos Cb.pos.DL wD Lb2

Cb.pos.LL wL Lb2

=

where Ca.neg Cb.neg Ca.pos.DL Ca.pos.LL Cb.pos.DL Cb.pos.LL

are tabulated moment coefficients

wD 1.2 DL= wL 1.6 LL=

wu 1.2 1.6 LL=

Example 17.3

Slab dimension La 5.0m 25cm 4.75 m

Lb 5.5m 20cm 5.3 m

Live load for office LL 2.40kN

m2

Materials f'c 20MPa fy 390MPa

Boundary conditions in short and long directions

Simple

Continuous

0

1

ShortContinuous

Continuous

LongContinuous

Continuous

Solution

Thickness of two-way slab

Perimeter La Lb 2

Page 124

tminPerimeter

180111.667 mm

t1

30

1

50

La 158.333 95( ) mm

Use t 120mm

Loads on slab

Cover 50mm 22kN

m3

1.1kN

m2

Slab t 25kN

m3

3kN

m2

Ceiling 0.40kN

m2

Partition 1.00kN

m2

SDL Cover Ceiling Partition 2.5kN

m2

DL SDL Slab 5.5kN

m2

wD 1.2 DL

LL 2.4kN

m2

wL 1.6 LL

wu 1.2 DL 1.6LL 10.44kN

m2

Moment coefficients

Page 125

Table 12.3aCoefficients for negative moments in short direction of slab

m Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 Case 7 Case 8 Case 91.00 0.000 0.045 0.000 0.050 0.075 0.071 0.000 0.033 0.0610.95 0.000 0.050 0.000 0.055 0.079 0.075 0.000 0.038 0.0650.90 0.000 0.055 0.000 0.060 0.080 0.079 0.000 0.043 0.0680.85 0.000 0.060 0.000 0.066 0.082 0.083 0.000 0.049 0.0720.80 0.000 0.065 0.000 0.071 0.083 0.086 0.000 0.055 0.0750.75 0.000 0.069 0.000 0.076 0.085 0.088 0.000 0.061 0.0780.70 0.000 0.074 0.000 0.081 0.086 0.091 0.000 0.068 0.0810.65 0.000 0.077 0.000 0.085 0.087 0.093 0.000 0.074 0.0830.60 0.000 0.081 0.000 0.089 0.088 0.095 0.000 0.080 0.0850.55 0.000 0.084 0.000 0.092 0.089 0.096 0.000 0.085 0.0860.50 0.000 0.086 0.000 0.094 0.090 0.097 0.000 0.089 0.088

Table 12.3bCoefficients for negative moments in long direction of slab

m Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 Case 7 Case 8 Case 91.00 0.000 0.045 0.076 0.050 0.000 0.000 0.071 0.061 0.0330.95 0.000 0.041 0.072 0.045 0.000 0.000 0.067 0.056 0.0290.90 0.000 0.037 0.070 0.040 0.000 0.000 0.062 0.052 0.0250.85 0.000 0.031 0.065 0.034 0.000 0.000 0.057 0.046 0.0210.80 0.000 0.027 0.061 0.029 0.000 0.000 0.051 0.041 0.0170.75 0.000 0.022 0.056 0.024 0.000 0.000 0.044 0.036 0.0140.70 0.000 0.017 0.050 0.019 0.000 0.000 0.038 0.029 0.0110.65 0.000 0.014 0.043 0.015 0.000 0.000 0.031 0.024 0.0080.60 0.000 0.010 0.035 0.011 0.000 0.000 0.024 0.018 0.0060.55 0.000 0.007 0.028 0.008 0.000 0.000 0.019 0.014 0.0050.50 0.000 0.006 0.022 0.006 0.000 0.000 0.014 0.010 0.003

ORIGIN 1

Index1

2

2

3

I IndexShort1 1 Short2 1 3

J IndexLong1 1 Long2 1 3

Table

1

6

5

7

4

9

3

8

2

Case TableI J 2

Vλ reverse Vλ( )

Vaneg reverse Taneg Case Vbneg reverse Tbneg Case

VaposDL reverse TaposDL Case VbposDL reverse TbposDL Case

VaposLL reverse TaposLL Case VbposLL reverse TbposLL Case

λLa

Lb0.896

vs1 pspline Vλ Vaneg( ) Ca.neg interp vs1 Vλ Vaneg λ( ) 0.055

Page 126

vs2 pspline Vλ Vbneg( ) Cb.neg interp vs2 Vλ Vbneg λ( ) 0.037

vs3 pspline Vλ VaposDL( ) Ca.pos.DL interp vs3 Vλ VaposDL λ( ) 0.022

vs4 pspline Vλ VbposDL( ) Cb.pos.DL interp vs4 Vλ VbposDL λ( ) 0.014

vs5 pspline Vλ VaposLL( ) Ca.pos.LL interp vs5 Vλ VaposLL λ( ) 0.034

vs6 pspline Vλ VbposLL( ) Cb.pos.LL interp vs6 Vλ VbposLL λ( ) 0.022

Bending moments

Ma.neg Ca.neg wu La2

13.043kN m

1m

Mb.neg Cb.neg wu Lb2

10.729kN m

1m

Ma.pos Ca.pos.DL wD La2

Ca.pos.LL wL La2

6.266kN m

1m

Mb.pos Cb.pos.DL wD Lb2

Cb.pos.LL wL Lb2

4.911kN m

1m

Steel reinforcements

β1 0.65 max 0.85 0.05f'c 27.6MPa

6.9MPa

min 0.85

0.85

εu 0.003

ρmax 0.85 β1f'c

fy

εu

εu 0.005 0.014

ρmin max

0.249MPaf'c

MPa

fy

1.379MPa

fy

0.00354

ρshrinkage 0.0020return( ) fy 50ksiif

0.0018return( ) fy 60ksiif

max 0.001860ksi

fy 0.0014

return

otherwise

ρshrinkage 0.0018

Top rebars in short direction

b 1m d t 20mm 10mm10mm

2

85 mm

Page 127

Mu Ma.neg b 13.043 kN m

Mn

Mu

0.914.492 kN m

RMn

b d2

2.006 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.005 ρ ρmax 1

As max ρ b d ρshrinkage b t 4.666 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

160 mm

Bottom rebars in short direction

Mu Ma.pos b 6.266 kN m

Mn

Mu

0.96.963 kN m

RMn

b d2

0.964 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.003 ρ ρmax 1

As max ρ b d ρshrinkage b t 2.163 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

Top rebars in long direction

Mu Mb.neg b 10.729 kN m

Mn

Mu

0.911.921 kN m

Page 128

RMn

b d2

1.65 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.004 ρ ρmax 1

As max ρ b d ρshrinkage b t 3.79 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

200 mm

Bottom rebars in long direction

Mu Mb.pos b 4.911 kN m

Mn

Mu

0.95.457 kN m

RMn

b d2

0.755 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.002 ρ ρmax 1

As max ρ b d ρshrinkage b t 2.16 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

Shrinkage rebars

b 1m

As ρshrinkage b t 2.16 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 5 t 450mm( )

s min Floorb

n10mm

smax

360 mm

Page 129

(3) Direct Design Method (DDM)

Total static moment

M0

wu L2 Ln2

8=

Longitudinal distribution of moments

Mneg Cneg M0=

Mpos Cpos M0=

Lateral distribution of moments

Mneg.col Cneg.col Mneg=

Mneg.mid Cneg.mid Mneg=

Mpos.col Cpos.col Mpos=

Mpos.mid Cpos.mid Mpos=

Page 130

Example 17.4

Slab dimension La 4m Lb 6m

Live load for hospital LL 3.00kN

m2

Materials f'c 25MPa fy 390MPa

Page 131

Solution

Section of beam in long direction

L Lb 6 m

h1

10

1

15

L 600 400( ) mm h 500mm

b 0.3 0.6( ) h 150 300( ) mm b 250mm

bb

hb

b

h

Section of beam in short direction

L La 4 m

h1

10

1

15

L 400 266.667( ) mm h 300mm

b 0.3 0.6( ) h 90 180( ) mm b 200mm

ba

ha

b

h

Determination of slab thickness

Perimeter La Lb 2

tminPerimeter

180111.111 mm

Assume t 120mm

In long direction

bw bb h hb hf t

hw h hf

b min bw 2 hw bw 8 hf 1.01 m

A1 bw h x1h

2

A2 b bw hf x2

hf

2

xc

x1 A1 x2 A2

A1 A2169.852 mm

I1

bw h3

12A1 x1 xc 2

I2

b bw hf3

12A2 x2 xc 2

Page 132

Ib I1 I2 4.617 105

cm4

Is

La hf3

12

wc 24kN

m3

Ec 44MPawc

kN

m3

1.5

f'c

MPa 2.587 10

4 MPa

αEc Ib

Ec Is8.016 αb α

In short direction

bw ba h ha hf t

hw h hf

b min bw 2 hw bw 8 hf 0.56 m

A1 bw h x1h

2

A2 b bw hf x2

hf

2

xc

x1 A1 x2 A2

A1 A2112.326 mm

I1

bw h3

12A1 x1 xc 2

I2

b bw hf3

12A2 x2 xc 2

Ib I1 I2 7.053 104

cm4

Iba Ib

Is

Lb hf3

128.64 10

4 cm

4

αEc Ib

Ec Is0.816 αa α

Required thickness of slab

αm

αa 2 αb 2

44.416

βLb

La1.5

Ln Lb 20cm 5.8 m

Page 133

hf max

Ln 0.8fy

200ksi

36 5 β αm 0.2 5in

0.2 αm 2.0if

max

Ln 0.8fy

200ksi

36 9 β3.5in

2.0 αm 5.0if

"DDM is not applied" otherwise

hf 126.876 mm

Loads on slab

DL 50mm 22kN

m3

t 25kN

m3

0.40kN

m2

1.00kN

m2

5.5kN

m2

LL 3kN

m2

wu 1.2 DL 1.6 LL 11.4kN

m2

In long direction

L1 Lb 6 m Ln L1 ba 5.8 m

L2 La 4 m α1 αb 8.016

Total static moment

M0

wu L2 Ln2

8191.748 kN m

Longitudinal distribution of moments

Mneg 0.65 M0 124.636 kN m

Mpos 0.35 M0 67.112 kN m

Lateral distribution of moments

k1

L2

L10.667 k2 α1

L2

L1 5.344

linterp2 VX VY M x y( )

Vj

linterp VX M j x

j 1 rows VY( )for

linterp VY V y( )

Page 134

Cneg.col linterp2

0

1

10

0.5

1.0

2.0

0.75

0.90

0.90

0.75

0.75

0.75

0.75

0.45

0.45

k2 k1

0.85

Cneg.mid 1 Cneg.col 0.15

Cpos.col linterp2

0

1

10

0.5

1.0

2.0

0.60

0.90

0.90

0.60

0.75

0.75

0.60

0.45

0.45

k2 k1

0.85

Cpos.mid 1 Cpos.col 0.15

Mneg.col Cneg.col Mneg 105.941 kN m

Mneg.mid Cneg.mid Mneg 18.695 kN m

Mpos.col Cpos.col Mpos 57.045 kN m

Mpos.mid Cpos.mid Mpos 10.067 kN m

Ccol.beam linterp

0

1

10

0

0.85

0.85

k2

0.85

Ccol.slab 1 Ccol.beam 0.15

Mneg.col.beam Ccol.beam Mneg.col 90.05 kN m

Mneg.col.slab Ccol.slab Mneg.col 15.891 kN m

Mpos.col.beam Ccol.beam Mpos.col 48.488 kN m

Mpos.col.slab Ccol.slab Mpos.col 8.557 kN m

bcol

min L1 L2 4

2 2 m

bmid L2 bcol 2 m

Top rebars in column strip

b bcol d t 20mm 10mm10mm

2

85 mm

Mu Mneg.col.slab 15.891 kN m

Mn

Mu

0.917.657 kN m

Page 135

RMn

b d2

1.222 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.003 ρ ρmax 1

As max ρ b d ρshrinkage b t 5.489 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

Bottom rebars in column strip

Mu Mpos.col.slab 8.557 kN m

Mn

Mu

0.99.508 kN m

RMn

b d2

0.658 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.002 ρ ρmax 1

As max ρ b d ρshrinkage b t 4.32 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

Top rebars in middle strip

b bmid

Mu Mneg.mid 18.695 kN m

Mn

Mu

0.920.773 kN m

RMn

b d2

1.438 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.004 ρ ρmax 1

Page 136

As max ρ b d ρshrinkage b t 6.494 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

Bottom rebars in middle strip

Mu Mpos.mid 10.067 kN m

Mn

Mu

0.911.185 kN m

RMn

b d2

0.774 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.002 ρ ρmax 1

As max ρ b d ρshrinkage b t 4.32 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

In short direction

L1 La 4 m Ln L1 bb 3.75 m

L2 Lb 6 m α1 αa 0.816

Total static moment

M0

wu L2 Ln2

8120.234 kN m

Longitudinal distribution of moments

Mneg 0.65 M0 78.152 kN m

Mpos 0.35 M0 42.082 kN m

Lateral distribution of moments

Page 137

k1

L2

L11.5 k2 α1

L2

L1 1.224

Cneg.col linterp2

0

1

10

0.5

1.0

2.0

0.75

0.90

0.90

0.75

0.75

0.75

0.75

0.45

0.45

k2 k1

0.6

Cneg.mid 1 Cneg.col 0.4

Cpos.col linterp2

0

1

10

0.5

1.0

2.0

0.60

0.90

0.90

0.60

0.75

0.75

0.60

0.45

0.45

k2 k1

0.6

Cpos.mid 1 Cpos.col 0.4

Mneg.col Cneg.col Mneg 46.891 kN m

Mneg.mid Cneg.mid Mneg 31.261 kN m

Mpos.col Cpos.col Mpos 25.249 kN m

Mpos.mid Cpos.mid Mpos 16.833 kN m

Ccol.beam linterp

0

1

10

0

0.85

0.85

k2

0.85

Ccol.slab 1 Ccol.beam 0.15

Mneg.col.beam Ccol.beam Mneg.col 39.858 kN m

Mneg.col.slab Ccol.slab Mneg.col 7.034 kN m

Mpos.col.beam Ccol.beam Mpos.col 21.462 kN m

Mpos.col.slab Ccol.slab Mpos.col 3.787 kN m

bcol

min L1 L2 4

2 2 m

bmid L2 bcol 4 m

Top rebars in column strip

b bcol

Mu Mneg.col.slab 7.034 kN m

Mn

Mu

0.97.815 kN m

Page 138

RMn

b d2

0.541 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.001 ρ ρmax 1

As max ρ b d ρshrinkage b t 4.32 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

Bottom rebars in column strip

Mu Mpos.col.slab 3.787 kN m

Mn

Mu

0.94.208 kN m

RMn

b d2

0.291 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.001 ρ ρmax 1

As max ρ b d ρshrinkage b t 4.32 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

Top rebars in middle strip

b bmid

Mu Mneg.mid 31.261 kN m

Mn

Mu

0.934.734 kN m

RMn

b d2

1.202 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.003 ρ ρmax 1

Page 139

As max ρ b d ρshrinkage b t 10.792 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

Bottom rebars in middle strip

Mu Mpos.mid 16.833 kN m

Mn

Mu

0.918.703 kN m

RMn

b d2

0.647 MPa

ρ 0.85f'c

fy 1 1 2

R

0.85 f'c

0.002 ρ ρmax 1

As max ρ b d ρshrinkage b t 8.64 cm2

As0π 10mm( )

2

4 n

As

As0 smax min 2 t 450mm( )

s min Floorb

n10mm

smax

240 mm

Page 140

Page 141