ET 1 of 3

DESIGN OF SEPTIC TANK (200 USERS)1 SEPTIC TANK( R.C.C)

Size of sump : 6x 2.9 x 2.015M depth + 0.3M Free Board

Data: 2.2222

Length 6 m

Bredth 2.9 m 2.7

Depth 2.038 m avg depth 2.0375Free Board 0.3 m

Assumed thickness of Base Slab 0.3 m

Assumed thickness of cover Slab 0.125 m

Assumed Side Wall thickness 0.2 m

Concrete grade 30

Grade of Steel 500

Unit weight of water 10

Unit weight of soil 18

Unit weight of Concrete 25

Projection of base slab Y 0.25 m

Pipes & other fixtures Load 100 Kn

SBC 80

Edge coefficient 0.1

Clear cover for Wall 0.025 m

Area of Bottom Slab 22.1 Sqm

Dia of Bars for Base Slab 10 mm

Dia of Bars for Side walls 10 mma) Design of Bottom slab( Using uncracked theory)

Load transformed to Foundation

Load from water(L x B x H x Unit Weight of water) 354.525

249.645 206.1675

54.375

156.6Pipes & other fixtures 100

Total 915.145 KN 69.185

Pressure on soil 41.40928 SAFE

i) When tank is Empty

Up ward pressure on base slab W 25.367

As a two way slab 1.91 Two way

Bending Moment Coefficient from table 22 of IS 456 16.04186

Negative ( N)

***** Enter the value from table 26 of IS 456 0.087

0.087 16.04 3.1 = 13.41 KN-M

0 16.04 3.1 = 0.00 KN-M

K=Effective depth( d') /Total depth(d) 0.92

***** As per uncracked theory = 0.3*****

13.41 x 1000 x 1000

overall thickness 0.3 x 1000 = 211.44 mm

***** Provided thickness = 0.25 m or 250 mm

Effective depth Provided = 205 mm

= 501.34

Area of Steel Required = 501.34

Spacing required = 156.58

Provided Spacing = 100 c/c safe

provide # 10@100c/c in shorter span and # 10@ 100 c/c in long span

Check for minimum reinforcement for base slab

Percentage of steel coefficients 0.24

= 50.75

Required minimum area of steel = 507.46 mm2 safe

N/mm2

N/mm2

Kn/m3

Kn/m3

Kn/m3

KN/m2

Self weight of Side Wall ( L x H x Thick x Unit wt of Concrete)Weight of cover slab (L+Y)X(B+Y) X Depth x (Unit Weight of Concrete)Weight of base slab (L+Y)X(B+Y) X Depth x (Unit Weight of Concrete)

KN/m2

KN/M2

ly/lx

Positive (P)

Mx ( + Ve)= P x W x (Lx)2

Mx ( - Ve)= N x W x (Lx)2

M/bD2

cm2

mm2

cm2

ET 2 of 3

b) Design of side wall

Ratio Breadth(b)/Depth ( a) = 2.9=

1.42

2.0375

Asper Is 3370 part IV

0.01 10.00 8.458 = 0.85 KN-M

0.041 10.00 8.458 = 3.47 KN-M

0.016 10.00 8.458 = 1.35 KN-M

0.012 10.00 8.458 = 1.02 KN-M

K=Effective depth( d') /Total depth(d) = 0.99

As per uncracked theory = 0.3

3.47 x 1000 x 1000

overall thickness 0.3 x 1000 = 107.52 mm

200.00

effective depth provided < = 155.00 mm

Provide overal Thickness = 200.00 mm

Area of Steel Required (vertical) 66.91

= 66.91

Spacing required = 1173.27 mm

Provided vertical reinforcement Spacing = 150 c/c safe

Area of Steel Required (horizontal) 171.45

= 171.45

Spacing required = 457.86 mm

Provided horizontal reinforcement Spacing = 150 c/c safe

Check for minimum reinforcement for side wall

Percentage of steel coefficients 0.24

Required minimum steel = 372.00

Provide 10mm @150c/c

Check for tension on wall

From Table 8 of 3370-Part IV

Wall coefficient = 0.59

Tension on wall = 24.493 Kn

Permissable tensile stress = 150 N/mm2

Ast = 163.289 mm2

provide 8@ 150c/c in long span

Roof Slab

Slab thickness assumed is = 125 mm

clear cover taken as = 20 mm

assumed dia of bar = 8 mm

where effective depth = 101 mm

The panel size is = 6.13 x 3.03 c/c

l/b = 2.02

Concrete Mix = M30

Density of concrete = 25

Load On slab

self weight = 3.125

Floor finish = 1.5

Live Load = 2

Total Load on Slab = 6.625 6.70

Considering the slab as discontinuous in three sides

As per code IS 456

Short span +ve moment Mx = = 7.234 KN-m

Long span +ve moment My = = 1.778 KN-m

0.118

0.029

Percentage of steel is =

% of steel is along shorter span = 0.71

% of steel is along Longer span = 0.17

From sp16 Table 1

= 0.178

= 0.07

Area of steel Required (Ast) =100

Ast along short span = 179.78 ~ 206.75

Ast along Long span = 70.70 ~ 81.31

For dia of bar = 8

spacing required along short span = 243.00 ~ 200 c/c

spacing required along Long span = 617.920 ~ 200 c/c

Mx ( + Ve)= P x W x (Lx)2

Mx ( - Ve)= N x W x (Lx)2

My ( + Ve)= P x W x (Lx)2

My ( - Ve)= N x W x (Lx)2

M/bD2

mm2

mm2

mm2

w x a2

KN/m3

KN/m2 ~ KN/m2

αxwlx2

αywlx2

where αx =

where αy =

Mu

(bxd2)

Percentage of steel for Short span (Pt)

Percentage of steel for Long span (Pt)

(Pt x b x d)

mm2

mm2

ET 3 of 3

provide #8@ 200 c/c in shorter span and # 8@ 200 c/c in long span