5.1 Design of Sanitary Wastewater Manholes_1456

5.1 Design of Sanitary Wastewater Manholes Purpose of Calculation : The : The purpose of this calculation is to determine the size of manholes, thickness of wall, cover slab and base slab. Assumptions: 1. Assume water table is 1 meter below finish grade.

Diagram: Tw

B

Tw

Ts

Tw H W Tw

Tb PLAN

 Assume manhole size B= 1.20 m

SECTION

Ts =

0.25

m

W=

1.20

m

Tw =

0.30

m

H=

2.20

m

Tb =

0.30

m

Design Parameters Unit weight of concrete ( yc )

=

24

kN/m

Unit weight of submerged soil ( ys )

=

10.5

kN/m

Unit weight of dry soil ( ys1 )

=

18

kN/m

Unit weight of water ( yw )

=

10

kN/m

Soil Bearing Capacity ( SBC )  Angle of internal friction ( f ) Coefficient of friction bet soil & conc ( m ) Compressive strength of concrete ( f'c )

= = = =

100 30 0.4 27.58

kN/m deg

Yield strength of rebars ( f y )

=

414

MPa

Live load surcharge ( s )

=

10

kN/m

2

MPa 2

Vertical Loads ( Wt ) W mh = Weight of manhole = W 1 + W 2 + W 3 W 1 = Weight of slab =  ( yc ) ( B W Ts ) =

8.64

kN

W 2 = Weight of walls =  ( yc ) [ ( 2 B H Tw ) + ( 2 W 1 H Tw ) ]

=

95.04

kN

W 3 = Weight of base slab =  ( yc ) ( B1 W 1 Tb ) = W mh =

127.01

23.33

kN

31.68

kN

kN

W w = Weight of water  =  ( yw ) ( B W H ) W t =

158.69

=

kN

Actual soil bearing pressure ( q a ) ( Full of water ) qa = W t / A  A = W 1 B1 = 3.24 kN/ kN/m < 48.98 100 Factor of safety against uplift ( empty ) FS = W e / Fu qa =

kN/m kN/m

2

2

Mu = wu L  / 8

L=

( SAFE SAFE ) Fu = (yw) [(B + 2 Tw) (W + 2 Tw) (H + Tb - 1)]

2.61 > 1.2 ( SAFE ) Design of slab Considering 1 meter strip of slab DL = yc Ts = 6.00 kN/m kN/m = LL = 3.60 wu = 1.4 DL + 1.7 LL =

m

=

3.60 14.52

kN/m kN/m

1.20

m

= 2.61 kN-m Required Depth ( d ) Mu d=

kN

f =

0.90

b=

1000

mm

f'c =

27.58

MPa

f y =

414

MPa

b =

0.85

Mu

f =

0.90

f d f y [ 1 - 0.59 ( r f y / f'c ) ]

b= d= Ts =

1000 165 250

f b Ru

Ru = r f y [ 1 - 0.59 ( r f y / f'c ) ] r= 0.75 rb rb =

48.60

0.85 f'c b 600 =

0.02848

f y ( 600 + f y ) r = rmin =

Ru = d=

0.02136 1.4 / f y = 7.170 20.12

Reinforcing Bars As =

0.00338

<

MPa mm <

165

0.02136 mm ( SAFE )

= 52.43 mm ² Asmin = 0.0018 b Ts mm² < As = 450 Using 16 mm diameter bar;As16 = S= Use

444.44 200

200

mm mm on center  top and bottom

mm²

f'c = fy = r = Mu =

mm mm mm

27.58 MPa 414 MPa 0.02136 2.61 kN-m

Design of wall Pressure Coefficients: Active pressure Ka = ( 1 - sin f ) / ( 1 + sin f ) Ka =

0.33 Considering 1 meter strip of wall Lateral pressure on wall (submerge soil) Height of surcharge, h = surcharge / density of soil h= 0.95 m Submerged soil 2 F1 = (1/2) Ka ys ( H + h ) ( 1 ) = 17.39 Sea water  2 F2 = (1/2) Ka yw H ( 1 ) = 8.07 25.46 Lateral pressure on wall (dry soil) Height of surcharge, h = surcharge / density of soil h1 = 0.56 m Dry soil 2 F3 = (1/2) Ka ys1 ( H + h1) ( 1 ) = 22.78

0.95

surcharge

2.20

F1

kN kN kN (g (govern)

kN

F2

(1/2) Ka ys (H+h)

2

(1/2) Ka yw H

2

M = 0.128 F1 ( H + h ) + 0.128 F2 H = 9.29 kN-m Mu = 1.7 M = 15.79

kN-m

Required Depth ( d ) Mu d=

f =

0.90

b=

1000

mm

mm

Ru =

7.17

MPa

( SAFE )

Mu =

15.79

kN-m

f b Ru

d=

49.47

mm <

215

Reinforcing Bars ( vertical ) As = Mu

d=

215

mm

Tw = f'c = fy =

300 27.58 414

mm MPa MPa

r =

0.02136

f =

0.90

b=

1000

mm

mm

Ru =

7.17

MPa

( SAFE )

Mu =

9.99

kN-m

Mu

d=

215

mm

f d f y [ 1 - 0.59 ( r f y / f'c ) ]

Tb = f'c = fy =

300 27.58 414

mm MPa MPa

r =

0.02136

f d f y [ 1 - 0.59 ( r f y / f'c ) ]

= 243.11 mm² Asmin = 0.0018 b Tw mm² < As = 540 Using 16 mm diameter bar;As16 = S= Use

370.37 200

200

mm²

mm mm on center each face

Reinforcing Bars ( horizontal ) Asmin = 0.0025 b Tw mm² < As = 750 Using 16 mm diameter bar;As16 = S= Use

267 200

200

mm²

mm mm on center each face

Design of base Considering 1 meter strip of base 1.20

48.98 2

M = qa L  / 12 L= 1.20 = 5.88 KN-m Mu = 1.7 M = 9.99 kN-m

m

Required Depth ( d ) Mu d= f b Ru

d=

39.35

Reinforcing Bars  As =

mm <

215

= 153.82 mm² Asmin = 0.0018 b Tb mm² < As = 540 Using 16 mm diameter bar;As16 = S= Use

370.37 200

200

mm²

mm mm on center top & bottom bars bothways