water tank resting on ground

8/11/2019 Water Tank Resting on Ground

1/4

0.25

Elevation details: Basin top 1.169m EL

Elevation of the ground EL-ground= -0.3 m

Top of the basin EL-Top= 1.169 m WL 0.969m EL

Bottom of the basin EL-Bottom= -0.25 m GL -0.3m EL

Free board above the water level = 0.2 m

Ht of the soil on the outer side of the wall hs= 0.4 m

Ht of the water on the inner side of the wall hw= 1.219 m 1.419

Height of the wall H= 1.419 m

Thickness of the wall at bottom Dtb= 0.25 m

Thickness of the wall at top Dtt= 0.25 m

Thickness of the wall footing tf= 0.45 m Basin bottom -0.25m EL

Outer projection of the footing pj1= 0 m 0.45 0.25

Inner projection of the footing pj2= 0.75 m

Width of the wall footing W= 1 m 0 0.25 0.75

Thickness of the base slab ts= 0.25 m

Height of soil above pj1 hs1= 0 1

Plan details:

Length of the basin L= 13.274 m

Breadth of the basin B= 5.532 m

L/B= 2.399494 >2

B/H= 3.89852 >3

FALLS UNDER THE CATEGORY L/B>2 AND B/H>3

Properties: Modular ratio m= 10.9803922

Unit weight of the soil wts= 18 kN/m3

Neutral axis constant k= 0.38356164

Unit weight of the water wtw= 9.807 kN/m3

Lever arm constant j= 0.87214612

unit weight of concrete wc= 25 kN/m3

M.R constant Q= 1.42171765

Grade of concrete = M25Grade of steel = Fe415

Maximum tensile stress in steel sst= 150 N/mm2

Angle of repose of the soil 30 degrees

Active pressure co-efficient Ca= 0.333333

Safe bearing capacity of the soil SBC= 117.684 kN/m2

In our procedure, we are considering the soil as saturated soil for a conservative design.

Two-cases have to be checked.

Case-I: basin EMPTY- PRESSURE OF SOIL ACTING FROM OUTSIDE AND NO WATER PRESSURE FROM INSIDE

Case-II: basin FULL-PRSSURE OF WATER ACTING FROM INSIDE AND NO EARTH PRESSURE FROM OUTSIDE

Loads calculated per meter run of the wall

Case-I: Case-II:

Check against overturning: Check against overturning:

Force due to active pressure Fa= 1.00304 kN Force due to active pressure Fa= 7.28641 kN

Overturning moment Mo2= 0.2841947 kN-m Overturning moment Mo= 2.960711 kN-m

Resisting forces and their line of action Resisting forces and their line of action

Permissible stress inconcrete to resist cracking

in tension due to bending

N/mm2

stbc=

1.27491

Permissible stress in

concrete to resist cracking

in direct tension N/mm2

sct

Co-efficient of friction between the soil and

the concrete = 0.5

COOLING TOWER BASIN RESTING AT GROUND WITH L/B>2 AND H/B>3

The long walls will be designed as cantilevers and short wall slabs supported by long walls. Bottom 1m of short wall shall be designed as cantilever.

Max compressive strength of concrete in

bending scbc= 8.5 N/mm2

1.76526


2/4

Force kN

Distance

from heel

m

Moment

kN-m Force kN

Distance

from toe m

Moment

kN-m

0 0.75 0 triangular portion of the stem 0 0.25 0 triangular portion of the stem

8.86875 0.875 7.760156 rectangular portion of the stem 8.86875 0.125 1.108594 rectangular portion of the stem

11.25 0.5 5.625 footing weight 11.25 0.5 5.625 footing weight0 1 0 soil weight 8.96605 0.625 5.603781 water weight

-3.9228 0.5 -1.9614 uplift due to water -4.41315 0.5 -2.206575 uplift due to water

F=16.196kN M=11.424kN-m F=24.672kN M=10.131kN-m

Factor of safety for uplift F.S.u= 5.1286708 Factor of safety for uplift F.S.u= 6.590485

>1.5, Hence safe for uplift >1.5, Hence safe for uplift

Factor of safety for overturning F.So= 36.177247 Factor of safety for overturning F.So= 3.079571

>1.4, Hence safe >1.4, Hence safe

Check for soil pressure at footing base: Check for soil pressure at footing base:

Vertical reaction -R=F R= 16.19595 kN Vertical reaction -R=F R= 24.67165 kN

Distance of R from heel Lr= 0.7228937 m Distance of R from toe Lr= 0.53063 m

Eccentricity e= 0.2228937 m Eccentricity e= 0.03063 m

Maximum pressure at base pmax= 37.855806 kN/m

2

Maximum pressure at base pmax= 29.20577 kN/m

2

Minimum pressure at base pmin= -5.463906 kN/m2

Minimum pressure at base pmin= 20.13753 kN/m2

80%, Hence Safe

Check for sliding: Check for sliding:

Sliding force Fs=Fa Fs= 1.00304 kN Sliding force Fs=Fa Fs= 7.28641 kN

Resisting force = F F= 8.097975 kN Resisting force = F F= 12.33582 kN

Factor of safety for sliding F.S.s= 8.0734318 Factor of safety for sliding F.S.s= 1.692991

>1.2, Hence Safe >1.2, Hence Safe

-5.463906 20.13753

37.85581 29.20577

Total Downward pressure = 16.713906 kN/m2

Total Downward pressure = 3.0672 kN/m2

Total upward pressure = 26.605806 kN/m2

Total upward pressure = 17.95577 kN/m2

Design of wall footing:

Bottom reinforcement:(upward pressure)

Bending moment B.Md= 19.95435 kN-m

Depth required for no cracking D= 0.260429 m


3/4

Provide 12 dia bar with spacing 175mm as distribution reinforcement along the bottom

Top reinforcement:(downward pressure)

Bending moment B.Md= 2.3004 kN-m



4/4

Provide 12 dia bar with spacing 175mm as distribution reinforcement on both sides of the wall

Design of Short wall:

Critical section for short wall design is at 1m or h/4 distance above the ground whichever is greater

Critical height hc= 1 mCase-I:

Pressure due to submerged soil ps= 3.53432 kN/m

(per metre length of the wall)

B.M at the base of the wall B.M= 0.094249 kN-m


< Provided thickness of the wall =0.25m, Hence safe

Clear cover of the wall ccf= 0.04 m min. % of steel 0.12857143 %

Diameter of the main reinforcement dia-fbm= 12 mm area of min. steel 321.428571

Effective depth of the wall footing deff-f= 0.204 m No. of bars Cal 3

Area of steel required Ast-fbm= 3.531538 mm2

Calculated spacing 333.333333

Spacing = 175 mm

Provide 12 dia bar with spacing 175mm as main reinforcement on outer side of the wall

Case-II:

Pressure due to water pw= 8.424759 kN/m

(per metre length of the wall)

B.M at the base of the wall B.M= 2.086477 kN-m


< Provided thickness of the wall =0.25m, Hence safe

Clear cover of the wall ccf= 0.04 m min. % of steel 0.12857143 %

Diameter of the main reinforcement dia-fbm= 12 mm area of min. steel 321.428571

Effective depth of the wall footing deff-f= 0.198 m No. of bars Cal 3

Area of steel required Ast-fbm= 80.55045 mm2

Calculated spacing 333.333333

Spacing = 175 mm

Provide 12 dia bar with spacing 175mm as main reinforcement on liquid side of the wall

Distribution steel: h/4 0.35475

min. % of steel 0.12857143 %

kN area of min. steel 321.428571

Area of distribution for tension = 181.8154 mm2

No. of bars Cal 3

Clear cover of the wall ccf= 0.04 m Calculated spacing 333.333333

Diameter of the main reinforcement dia-fbm= 12 mm

Spacing = 175 mm

Provide 12 dia bar with spacing 175mm as distribution reinforcement on both sides of the wall

Design of Base Slab:

Clear cover of the base slab ccbs= 0.05 m area of min. steel 321.428571

Diameter of the main reinforcement dia-fbm= 12 mm No. of bars Cal 3Effective depth of the base slab deff-f= 0.194 m Calculated spacing 333.333333

% area of main reinforcement on each face = 0.128571

Spacing = 200 mm

Provide 12 dia bar with spacing 200mm as main reinforcement on top and bottom of the base slab and on both directions

Direct tension at greater of 1m or H/4 distance

from the base of the wall = 27.27232

water tank resting on ground

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