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TitleWater-Tank-Design.pdf
Tags Stress (Mechanics) Bending Building Engineering
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Table of Contents
                            CHAPTER 7
WATER TANK
	7.1 INTRODUCTION
	7.2 TYPES OF WATER TANK
	
	
	7.3 BASIS OF DESIGN
	7.4 CIRCULAR TANK
		7.4.1    PERMISSIBLE STRESSES IN CONCRETE
		7.4.2    THE PERMISSIBLE STRESS IN STEEL
		7.4.3    BASE FOR FLOOR SLAB
		7.4.4    DESIGN METHOD
		7.4.4.1    Mr. H Carpenter’s method
		DESIGN PROCEDURE:
		Step 1:  Dimensions
		
		
		
		
		
		
		
		
		
		Step 2:  Determination of the value of coefficient F and k
		Step 3:
		
		Step 4:
		7.4.4.2    Approximate Method
		6.4.4.3    I.S. Code   Method
	7.5 RECTANGULAR TANKS
		6.5.1    DESIGN OF SIDE WALLS
		Tank wall having ratio of L/B lesser than 2:
		
		Tank wall having ratio of L/B greater then 2:
		
		Reinforcement:
		Analysis of Tank Wall Section Subjected To Combined Effect Of Bending And Direct Tension
		Step 1:
		
		6.5.2    DESIGN OF BASE SLAB
		
		6.5.3    DESIGN OF ROOF
		6.5.4    DESIGN OF UNDERGROUND RECTANGULAR TANK
		
		Design of long walls
		Design of short wall
		Design of slab
		Minimum reinforcement
	7.6 DESIGN OF A ROOF TOP WATER TANK
		Design Data:
		
		Step 1:
		
		Step 2:
		
		Step 3:
		
		
		
		
		
		
		
		Step 4:
		Step 5:
		Step 6:
		
		Step 7:
		Step 8:  Detailing
	7.7 DESIGN OF UNDERGROUND WATER TANK
		General data:
		Step 1:  Tank dimension
		
		
		Step 2:  Design of long walls
		Step 3:  Vertical reinforcement (long walls)
		
		Step 4:  Horizontal reinforcement (long walls)
		Step 5:   Design of shot wall
		Step 6: Vertical reinforcement (shot wall)
		
		Step 7: Horizontal reinforcement (shot wall)
		Step 8:   Design of base slab
		
		
		
		
		
		
		
		
		
		
		
		Step 9:  Detailing
                        
Document Text Contents
Page 1

CHAPTER 7

WATER TANK



7.1 INTRODUCTION


As per Greek philosopher Thales, “Water is the source of every creation.” In day to day life one
cannot live without water. Therefore water needs to be stored for daily use. Over head water tank
and underground water reservoir is the most effective storing facilities used for domestic or even
industrial purpose.

Depending upon the location of the tank the tanks can be named as overhead, on ground or
underground. The tanks can be made in different shapes usually circular and rectangular shapes
are mostly used. The tanks can be made of RCC or even of steel. The overhead tanks are usually
elevated from the roof top through column. In the other hand the underground tanks are rested on
the foundation. Different types of tanks and their design procedure is discussed in subsequent
portion if this chapter.

The water tanks in this chapter are designed on the basis of no crack theory. The concrete used
are made impervious.


7.2 TYPES OF WATER TANK


Basing on the location of the tank in a building s tanks can be classified into three categories.
Those are:


Underground tanks
Tank resting on grounds
Overhead tanks


In most cases the underground and on ground tanks are circular or rectangular is shape but the
shape of the overhead tanks are influenced by the aesthetical view of the surroundings and as
well as the design of the construction.

Steel tanks are also used specially in railway yards. Basing on the shape the tanks can be
circular, rectangular, square, polygonal, spherical and conical. A special type of tank named
Intze tank is used for storing large amount of water for an area.

The overhead tanks are supported by the column which acts as stages. This column can be
braced for increasing strength and as well as to improve the aesthetic views.

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265



7.3 BASIS OF DESIGN


One of the vital considerations for design of tanks is that the structure has adequate resistance to
cracking and has adequate strength. For achieving these following assumptions are made:


Concrete is capable of resisting limited tensile stresses the full section of concrete
including cover and reinforcement is taken into account in this assumption.
To guard against structural failure in strength calculation the tensile strength of

concrete is ignored.
Reduced values of permissible stresses in steel are adopted in steel are adopted in

design.


7.4 CIRCULAR TANK


The simplest from of water tank is circular tank for the same amount of storage the circular tank
requires lesser amount of material. More over for its circular shape it has no corner and can be
made water tight easily. It is very economical for smaller storage of water up to 20000000 liters
and with diameter in the range of 5 to 8 m. The depth of the storage is between 3 to 4 m. The
side walls are designed for hoop tension and bending moments.


7.4.1 PERMISSIBLE STRESSES IN CONCRETE

To ensure impervious concrete mixture linear than M 20 grade is not normally recommended to
make the walls leak proof the concretes near the water face need to such that no crack occurs. To
ensure this member thicknesses are so designed that stress in the concrete is lesser then the
permissible as given in table 7.1.


7.4.2 THE PERMISSIBLE STRESS IN STEEL

The stress in steel must not be allowed to exceed the following values under different positions
to prevent cracking of concrete.


When steel is placed near the face of the members in contact with liquid 115 N/ sq
mm for ms Bars and 150 N/ sq mm for HYSD bars.
When steel is placed on face away from liquid for members less then 225 mm in

thickness same as earlier.
When steel is placed on the face away from the liquid for members 225 mm or

more in thickness: 125 N/ sq mm for M.S. bars and 190 N/sq mm for HYSD bars.

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281



6.5.4 DESIGN OF UNDERGROUND RECTANGULAR TANK


While designing an underground tank the most crucial condition of the tank need to be kept
under consideration. And that is when the empty and the soil surrounding the wall is wet. In this
case the wall has to sustain the soil pressure.


















Figure 7.8 : Soil Pressure on Tank




Design of long walls



Maximum bending moment occurs for the case tank empty and surrounding soil is water logged.
Long walls are designed as cantilever.

Page 19

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282
























Figure7.9 : Moment diagram in tank walls


Pressure exerted by wet soil


θ
θ

sin1
)sin1(

+


=
wh

P (7-23)


Considering 1m run in the tank wall


maxM (Tension near water face)=
2

5.33
1

ph (7-24)

maxM (Tension away from water face) =
2

15
1

ph (7-25)


Thickness of wall is determined from the cracking consideration


D= ⎟⎟



⎜⎜



b

M

ctσ
6

(7-26)


Steel area is calculated as follows


jd
M

A
st

s σ
= (7-27)

Page 36

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299

Section A-A

# 4 Bar @ 4 in c/c

#4 Bar @7 in c/c

# 4 Bar @ 8 in c/c


# 4 Bar @ 7 in c/c

# 4 Bar @8 in c/c

Page 37

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300



A

Figure 716: Detailing of example (continued)

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