Paper

Prof.R.V.R.K.Prasad, Akshaya B.Kamdi / International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 2, Issue 5, September- October 2012, pp.664-666
664 | P a g e
EFFECT OF REVISION OF IS 3370 ON WATER STORAGE
TANK
*Prof.R.V.R.K.Prasad ,**Akshaya B.Kamdi
*( K.D.K.College of Enggineering , Nagpur university)
ABSTRACT
Storage overhead tank are used to store
water. BIS has brought out the revised version
of IS 3370 ( part 1& 2) after a long time from its
1965 version in year 2009. This revised code is
mainly drafted for water tank. In this revision
important is that limit state method is
incorporated in design. This paper gives in
brief, the theory behind the design of circular
water tank using working stress method and
limit state method. In the end comparative
result of IS 3370 (1965) and IS 3370 (2009) is
given.
1 . INTRODUCTION
As per Greek philosopher Thales ,” water
is source of every creation.” In day to day life one
can not live without water. Therefore water needs
to be stored for daily used. Overhead water tank is
the most effective storing facility used for domestic
or even industrial purpose.
Depending upon the location of the tank the tanks
can be name as overhead ,on ground and
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 the column. In
most cases underground and on ground tanks are
circular or rectangular in shape but the shape of the
overhead tanks are influenced by the aesthetic view
in surroundings and as well as the design of the
construction. Steel tanks are also used specially in
railway yards. Storage reservoirs and overhead
tank are used to store water, liquid petroleum,
petroleum products and similar liquids. Reservoir is
a common term applied to liquid storage structure
and it can be below or above the ground level.
Reservoirs below the ground level are normally
built to store large quantities of water. The
overhead tanks are supported by column which act
as stage. This Overhead type are built for direct
distribution by gravity flow and are usually of
smaller capacity. After a long time IS 3370 is
revised from its 1965 version. In this revision
introduction of limit state design is the most
important addition.
2 . DESIGN REQUIREMENT OF
CONCRETE (I. S. I)
In water retaining structure a dense
impermeable concrete is required therefore,
proportion of fine and course aggregates to cement
should be such as to give high quality concrete.
Concrete mix weaker than M20 is not used. The
minimum quantity of cement in the concrete mix
shall be not less than 30 kN/m3
.The design of the
concrete mix shall be such that the resultant
concrete is subjected to efficiently impervious.
Efficient compaction preferably by vibration is
essential. The permeability of the thoroughly
compacted concrete is dependent on water cement
ratio. Increase in water cement ratio increases
permeability, while concrete with low water
cement ratio is difficult to compact. Other causes of
leakage in concrete are defects such as segregation
and honey combing.
3. PROBLEM DESCRIPTION
To model any structure the main aim is to
achieve the economy. Material saving results in
saving in construction cost. However
circularcylindrical tanks are more numerous than
any other type because they are simple in design
and can be easily constructed .
In present work total focus is given on preliminary
analysis and design of Circular Cylindrical water
tank by IS 3370: (1965) & IS 3370 :(2009) . The
grade of Concrete used is M30 and grade of Steel
used is Fe 415.The permissible concrete stresses in
calculation relating to resistance to cracking (for
direct tension) is 1.5 N/ mm2
The value of
permissible stress in Steel (in direct tension
,bending and shear) in IS 3370:(1965) σst is 150
N/mm2
and in IS 3370:(2009) σst is 130 N/mm2
.
The permissible concrete stresses in calculation
relating to resistance to cracking for shear is 2.2
N/mm2
The cylindrical water tank is basically
divided in two parts; first is wall and base slab.
Wall is design for maximum Hoop tension and
maximum Bending moment and checked for
bending tensile stress which govern the thickness
of wall .Base slab is design for maximum bending
moment and also checked for permissible tensile
stress in concrete to make the tank leak proof.

665 | P a g e
4. ANALYSIS AND DESIGN OF
CONTAINER WALL
4.1. Method of Analysis of Cylindrical wall
Following method are available for analysis of
circular tank.
1. Reissner’s method
2. Carpenter’s method
3. Approximate method
4. I.S. code method
4.2. Design of cylindrical wall
While designing walls of cylindrical tanks the
following points should be born in mind
(a) Wall of cylindrical tanks are either cast
monolithically with the base or set in grooves and
key ways. In either case deformation of wall under
influence of liquid pressure is restricted at end
above the base. Consequently, only part of
triangular hydrostatic load will be carried by ring
tension and part of the load at bottom will be
supported by cantilever action
(b) It is difficult to restrict rotation or settlement of
base slab and it is advisable to provide vertical
reinforcement as if the wall were fully fixed at the
base, in addition to the reinforcement required to
resist horizontal ring tension for hinge at base ,
conditions of walls, unless the appropriate amount
of fixity at the base is established by analysis with
due consideration to the dimension of base slab the
type of joint between the wall and slab and where
applicable the type of soil supporting the base slab.
5. ALYSIS AND DESIGN OF BASE SLAB
5.1 Analysis of base slab
When the circular tanks are elevated and
supported, the analysis and design of base slab
depend upon the manner in which it is supported if
the supporting tower consisting of columns placed
below the tank walls, usually no separate curved
beam is required over the column to support the
tank. The tank wall itself act as a curved beam, as
the depth of this beam is large only a few steel bar
at its bottom and top is all that is required as a
reinforcement for the beam section.
The base slab should however be suitably tied to
the walls by the vertical rods embedded properly in
the slab and the wall. When the flexible joint is
provided between the wall and slab, a separate
circular beam is required below the slab.
5.2 Design of base base
If the bottom of a circular tank is
supported around its periphery, it can be designed
as a circular slab simply supported at edges.
Although circular slab are not so commonly used in
building but they have wide application in water
tanks. In applying this theory to R.C. slab poisson’s
ratio may be taken to zero. This slab when loaded
deflected in form of a saucer and develops radial as
well as circumferential stress. The convex face of
slab has tensile stress and concave face of slab
compressive stress. Hence R/F should be placed on
the concave face near the surface to be more
effective. The best form of R/F will be radial and
circumferential to safe-guard the slab against
circular and radial crack respectively. An
alternative arrangement in form of mesh such that
the intensity of reinforcement in either direction of
the mesh is as required for the bigger of the radial
and circumferential stresses. The radial and
circumferential system of reinforcement become
essential near the periphery of the slab if the
stresses there are not negligible or if the slab is
fixed at edges.
6. ANALYSIS AND DESIGN OF TOP
DOME
A dome may be defined as a thin shell
generated by the revolution of a regular curve about
one of its axes. The shape of the dome depends on
the type of the curve and the direction of the axis of
revolution. In spherical and conoidal domes,
surface is described by revolving an arc of a circle.
The centre of the circle may be on the axis of
rotation (spherical dome) or outside the axis
(conoidal dome). Both types may or may not have
a symmetrical lantern opening through the top. The
edge of the shell around its base is usually provided
with edge member cast integrally with the shell.
Domes are used in variety of structures, as in the
roof of circular areas, in circular tanks, in hangers,
exhibition halls, auditoriums, planetorium and
bottom of tanks, bins and bunkers. Domes may be
constructed of masonry, steel, timber and
reinforced concrete. However, reinforced domes
are more common nowadays since they can be
constructed over large spans.
6.1. Analysis of top dome
Stresses to be considered in dome are
Meridional thrust , Hoop stress
6.2. Design of top dome
The domes are designed for the total
vertical load only. The term total vertical load
include the weight of the dome slab and that of
covering material ,if any over the slab the weight
of any other load suspended from the slab and live
load etc.
The minimum thickness of dome slab should not be
less than 80 mm and the minimum percentage of
steel should not be less than 0.3 %
7. ANALYSIS AND DESIGN OF TOP
RING BEAM
The ring beam is necessary to resist the
horizontal component of the thrust of the dome. To
bear this horizontal component of meridional
thrust a ring beam is provided at the base of dome
.

666 | P a g e
7.1. Design of top ring beam
The ring beam takes hoop tension and
transfer only vertical reaction to the supporting
walls.
8. CRACKWIDTH IN MATURE
CONCRETE
According to IS 3370:2009 following
assessments has given
8.1. Assessment of crack width in flexure
The design surface crack width should not
exceed the appropriate value i.e. 0.2 mm. Crack
width can be calculated by following formula
W = ( 3 acr εm )/ 1+{2 (acr – Cmin) /(D-x)
W = design surface crack widt
acr = distance from the point considered to the
surface of the nearest bar
εm = average strain at the level where the
cracking is being considered.
Cmin = minimum cover to the tension steel
D = overall depth of the member
x = depth of neutral axis
8.2. Average strain in flexure
The average strain at the level where
cracking is being considered is assessed by
calculating the apparent strain using characteristic
load and normal elastic theory. Where flexure is
predominant but some tension exists at the section ,
the depth of the neutral axis should be adjusted.
The calculated apparent strain , ε1 is then adjusted
to take into account the stiffening effect of the
concrete between cracks ε2.
εm = ε1 - ε2
8.3. Stiffening effect of concrete in flexure
For a limiting design surface crack width
of 0.2 mm
ε2 = bt (D-x)(a’-x) / 3 Es As (d-x)
where
ε1 = strain at the level considered
ε2 = strain due to the stiffening effect of concrete
between cracks
bt = width of section at the centroid of the tension
steel
D = overall depth of the member
x = depth of the member
Es = modulus of elasticity of reinforcement
As = area of tension reinforcement
d = effective depth
a’ = distance from the compression face to the
point at which the crack
8.4. Assesment of crackwidth in direct tension
In some reinforced concrete member like
tankwall direct tension due to applied loading may
act in combination with restrained to volume
change cause by temperature and shrinkage. This
can lead to significant cracking which should be
controlled in the interest of serviceability. cracking
due to direct tension is of somewhat more serious
because it cause clear separation of concrete
through the entire thickness of member.
9. CONCLUSION
The thickness of wall and depth of base
slab is comes to different for IS 3370:(1965) and IS
3370:(2009) because of the value of permissible
stress in Steel (in direct tension ,bending and
shear) IS 3370:(1965) value of σst is 150 N/mm2
and in IS 3370:(2009) σst is 130 N/mm2
. Design of
water tank by Limit State Method is most
economical as the quantity of material required is
less as compared to working stress method Water
tank is the most important container to store water
therefore, Crack width calculation of water tank is
also necessary.
REFERENCES
[1] Howarfd I .Epstein, M. ASCE (1976)
“Seismic Design of Liquid-storage
Tanks”, Journal of the structure Division,
American society of Civil Engineers, Vol.
102,No. ST
[2] Laurent M. Shirima”Reinforced block
water storage tanks”:22 WEDC
conference New Delhi, India 19
[3] Durgesh C. Rai1
“Review of code
Designing Forces for Shaft Supports of
Elevated Water Tanks
[4] Mark W.Holmberg,P.E(2009)” Structure
magazine”
[5] IS 3370 (Part1):1965 concrete structure
for storage of liquids-code of
practice
practice
practice
practice
for storage of liquids-code of practice
[10] IS 456:2000 Plain And Reinforced
Concrete – Code Of Practice
[11] “Treasure of R.C.C.Design”– Sushilkumar
[12] “Advance Reinforced Concrete Design”
2nd Edition N. Raju

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