DESIGN OF UNDERGROUND RECTANGULAR
CONCRETE WATER TANK
PROJECT REPORT
Submitted by
ANIRUDHA.B
714013103004
PALANIAPPAN.RM
714013103029
REVANTH KUMAR.S
714013103037
SRIRAM.S
714013103045
in partial fulfillment for the award of the degree
of
BACHELOR OF ENGINEERING
in
CIVIL ENGINEERING
SRI SHAKTHI INSTITUTE OF ENGINEERING AND TECHNOLOGY
COIMBATORE - 641062
ANNA UNIVERSITY: CHENNAI 600 025
OCTOBER 2016
BONAFIDE CERTIFICATE
Certified that this project report “DESIGN OF UNDER GROUND
RECTANGULAR CONCTERE WATER TANK” is the bonafide work of
“ANIRUDHA.B, PALANIAPPAN.RM, REVANTH KUMAR.S, SRIRAM.S” who carried
out the project work under my supervision.
SIGNATURE
SIGNATURE
Er. M. Ravichandran
Dr. D. Karunanidhi
HEAD OF THE DEPARTMENT
SUPERVISOR
DEPARTMENT OF CIVIL
ASSISTANT PROFESSOR
ENGINEERING,
DEPARTMENT OF CIVIL
SRI SHAKTHI INSTITUTE OF
ENGINEERING,
ENGINEERING AND TECHNOLOG,
SRI SHAKTHI INSTITUTE OF
COIMBATORE-62.
ENGINEERING AND TECHNOLOGY,
COIMBATORE-62
Submitted for the design project viva voce examination held on ……….at
Sri Shakthi Institute of Engineering and Technology, Coimbatore-62.
Internal Examiner
External Examine
ACKNOWLEDGEMENT
First and foremost, we place this design project work on the feet of GOD
ALMIGHTY who is the power of strength in each step of progress towards the
successful completion of my project.
We express deepest gratitude to our Chairman Dr. S. Thangavelu, for his
invaluable guidance and blessings.
We are very grateful to our Principal Dr. C. Natarajan, for providing us with
an environment to complete this project successfully.
We are very grateful to our Joint Secretary Mr. T. Sheelan and Director
Dr. R. Manian, for the encouragement to complete our project successfully.
We are deeply indebted to our Head of the Department Mr. S.
Ravichandran, who molded us both technically and morally for achieving greater
success in life.
We are very grateful to our Supervisor Dr. D. Karunanithi, for being
instrumental in the completion of my project with his valuable guidance.
We are very thankful to our Project Coordinator Er. S. Ravichandran, who
helped me in the completion of the project with his valuable guidance.
We are also thankful to all the staff members of our college and technicians
for their help in making this project a successful one.
Finally, we take this opportunity to extend our deep appreciation to our
Family and Friends, for all that meant to us during the crucial times of the
completion of our project.
ANIRUDHA.B
PALANIAPPAN.RM
REVANTH KUMAR.S
SRIRAM.S
i
TABLE OF CONTANTS
CHAPTER NO
1.
TITLE
PAGE NO
LIST OF TABLE
vi
LIST OF FIGURES
vii
LIST OF SYMBOLS
viii
INTRODUCTION
1
1.1 UNDERGROUND WATER TANK
1
1.2 IMPORTANCE OF UNDERGROUND
2
WATER TANK
1.3 DIFFERENT TYPES OF WATER TANKS
3
DEPENDING ON ITS LOCATION
1.4 DIFFERENCE BETWEEN CIRCULAR AND
4
RECTANGULAR WATER TANK
1.5 DIFFERENT TYPES OF WATER TANKS
5
BASED ON MATERIALS
1.5.1 PLASTIC
5
1.5.2 STEEL TANK
6
1.5.3 FIBRE GLASS
6
1.5.4 CONCRTE TANK
6
1.6 ADVANTAGES OF CONCRETE WATER
TANK
ii
7
1.6.1 COST
7
1.6.2 DETERIORATION/LIFESPAN/
8
DURABILITY
1.6.3 SIZE AND SHAPE
8
1.6.4 ENVIRONMENT CREDENTIALS 8
1.6.5 MERITS OF CONCRETE WATER 9
TANK
1.6.6 DEMERITS OF CONCRETE
9
WATER TANK
1.6.7 SITE PREPARATIONS
1.7 OBJECTIVES
2.
GENERAL DESIGN REQUIREMENTS
9
9
10
2.1 DESIGN REQUIREMENT OF WATER TANK 13
2.2 JOINTS IN LIQUID RETAINING
15
STRUCTURES
2.2.1 MOVEMENT JOINTS
15
2.2.2 CONTRACTION JOINTS
17
2.2.3 TEMPORARY JOINTS
18
2.2.4 SPACING OF JOINTS
18
2.3 FLOORS
20
2.4 WALLS
22
2.5 ROOF
24
2.6 MINIMUM REINFORCEMENT
25
2.7 FLEXIBLE BASE WATER TANK
26
iii
2.8 RIGID BASE TANK
26
2.9 DESIGN REQUIREMENTS FOR UNDER
27
GROUND WATER TANK
3.
ANALYSIS AND DESIGN
31
3.1 DETERMINATION OF FIELD DENSITY OF
31
SOIL BY CORE CUTTER
3.2 FIXED FUNNEL TEST
33
3.3 DESIGN OF RECTANGULAR
35
UNDERGROUND CONCRETE TANK
4.
CONCLUSION
49
5.
REFERENCE
50
iv
ABSTRACT
Water tanks and reservoirs are used to store liquids like water, petroleum or
chemicals. For any domestic and commercial purposes, water tanks are very basic
need to meet their day to day use. In this project an attempt is made to design the
rectangular underground tank, the tank is to maintain atmospheric temperature and
provided optimum height for easy pumping of water to overhead tank. Since it is
underground water tank the lateral earth pressure and water pressure also considered
for the design calculations, so the design is to be carried out as per IS code norms.
This project deals with analysis and design of under ground water tank of 2lakh liter
capacity. The design in this project comprises of side walls, base slab and roof slab.
The analysis and design of underground water tank is done using AutoCad. For this
design project limit state method is used.
v
LIST OF TABLES
TABLE NO.
TITLE
PAGE
2.1
PERMISSIBLE CONCRETE STRESS
12
3.1
FIXED FUNNEL TEST
34
3.2
BENDING MOMENT ON WATER FACE
AND EARTH FACE
3.3
38
BENDING MOMENT AT CENTER AND
SUPPORT
45
vi
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE NO
2.1
MOVEMENT JOINT
16
2.2
EXPANSION JOINT
17
2.3
SLIDING JOINT
18
2.4
CONTRACTION JOINT
18
2.5
TEMPORARY JOINT
19
2.6
SPACING OF JOINT
19
3.1
REINFORCEMENT OF PLAN
46
3.2
REINFORCEMNT OF SHORT
AND LONG WALL
47
vii
LIST OF SYMBOLS
φ - Angle of repose
σcbc – Permissible stress in concrete in bending
σst – Permissible stress in steel in tension
jd – Lever arm depth
m – Modular ratio
d – Overall depth
de – Effective depth
b – Breadth
W – Load at the structure
M – Bending moment
Mv – Bending moment at vertical direction
Mh – Bending moment at horizontal direction
At – Area of tensile steel
L – Length of the tank
B – Width of the tank
H – Overall height of the tank
viii
CHAPTER 1
INTRODUCTION
1.1 UNDERGROUND WATER TANK
Underground water tanks are structures which act as a reservoir for small
domestic or commercial buildings. Basic components of underground water tanks
are Base slab, Side walls, And Roof slab. Tanks are very ductile, enabling to
withstand seismic forces and varying water backfill. Tanks utilize material
efficiently – steel in tension, concrete in compression. Underground water tanks
have Low maintenance throughout the life as these are built with concrete, durable
material that never corrodes and does not require coatings when in contact with water
or the environment. The main advantage of underground water tank is that the
temperature is lower than the overhead tanks, which will reduce evaporation inside
water tank.
Underground water tank faces different type of loads compared to other structures,
they mainly face horizontal or lateral loads due to earth pressure and water pressure
or any liquid pressure which is been stored in the tank. The side walls of the
underground water tank will face greater load at the bottom and the load linearly
decreases towards the top.
The underground water tank not only faces loads inside the tank it also has to bear
the surcharge above the ground level. So the roof slab of the underground tank
should have enough strength to with stand the surcharge.
1
1.2 IMPORTANCE OF UNDERGROUND WATER TANK
• Seepage
It is very important to store water and not to lose it. The tank should
have a durable, watertight, opaque exterior and a clean, smooth interior.
Below ground tanks must also be plastered well and correctly installed,
otherwise they can collapse.
• Evaporation
All storage tanks should have a roof made from locally available
materials. A tight fitting top cover prevents evaporation.
• Safety
We should prevent mosquito breeding and keeps insects, rodents, birds
and children out of the tank. A suitable overflow outlet(s) and access for
cleaning are also important.
• Storage of water
It is very imperative for all tanks to store water because the main
process of the tank is to store water due to lack of running fresh water in all
areas.
• Emergency
Underground tanks are used as reservoirs where water is pumped to
overhead tanks. When water is not available it will help us store and use water.
2
1.3 DIFFERENT TYPES OF WATER TANKS DEPENDING ON ITS
LOCATION
(i)RESTING ON GROUND
• Deals with normal pressure of gravity and corresponding outward pressure of
water stored in water tank (Internal hydrostatic pressure)
• Pipes can be attached directly for irrigation purpose.
• Pumps can be attached depending on the usage.
• More economical than other type of tanks.
• No need for excavation.
(ii)OVERHEAD
• The water pressure to all the processes being supplied is held at a relatively
constant level.
• In power failure or pump failure pressure remains constant.
• At work any pipe can be taken for maintenance.
• If all the pumps are failed water pressure will be still for fire suppression and
other critical needs.
• Gravity plays an important role for the flow of water.
• Columns are provided for the support of tank.
(iii)UNDERGROUND
• Used as water reservoir for irrigation purpose.
• Used for rainwater harvesting.
• Difficulty in installation.
3
• It is protected from animals in forest areas.
• Pumps are needed for supply of water.
• Expensive compared to tanks resting on the ground.
• In case of fire the water will be safe underground.
1.4 DIFFERENCE BETWEEN CIRCULAR AND RECTANGULAR WATER
TANK.
1.4.1CIRCULAR:
It is the simplest form of water tank. For the same amount of storage
circular water tank requires less amount of materials compared to rectangular water
tank. It has no corner and can be made water tight easily. It is economical for smaller
storage of water up to 200000000 lits and with dia 5 to 8 m. Depth of the storage is
between 3 to 4 m. The side walls are designed for hoop tension and bending moment.
Round tanks is really a cylinder holding the water. Water exerts pressure equally in
all directions. When place in cylinder round water vessels can be constructed using
minimum thickness of wall. Circular water tanks can be transported and installed
easily.
Merits: Structural strength, Economic, Constant heat level, Clean and hygienic.
1.4.2RECTANGULAR:
Rectangular tanks are modular, fit in most yards. Large tanks of high
capacity can be constructed. It occupies less space compared to circular tanks.
Multiple units of water storage can be constructed using rectangular type tanks.
Merits: Occupy less space when multiple units used.
4
Provide longer travel distance for settling to occur.
1.5 DIFFERENT TYPES WATER TANKS BASED ON MATERIAL:
1.5.1 PLASTIC TANK:
Poly (plastic) water tanks are made from polyethylene; a UV stabilized
food grade plastic. The tanks are light, you only need a sand base to place them on,
and they come in a wide variety of colours and have a long serviceable life. Many
poly tanks carrying a 25 year warranty, although many claim 15 years is a very
realistic lifespan. They are also usually the second cheapest. One of the major
disadvantages of polyethylene is the material is made from petrochemicals. Even
after their serviceable life has ended, there's still a great big hunk of plastic that will
take generations to break down and will release toxins as it does so. However,
polyethylene tanks can still be easily recycled after 15 years, so it's just a matter of
breaking the tank up and then carting it away rather than trying to squeeze a few
more years out of one. Some poly tanks are made with a vertical seam - this is a
weak point that may cause splitting and subsequent water loss. Polyethylene water
tanks and fire don't really mix either - they'll just melt. This can be a real problem if
you're in a rural area and you need that water to fight a fire. The other issue is the
long term effects of drinking water stored for such a long time in this material.
Polyethylene tanks are relatively new on the market, it is not known if there are any
credible serviceable life studies that have been done in relation to these issues. Some
people do note a bit of an odd taste to the water if the tank is placed in full sun. Just
on that point - before purchasing a poly tank, check the warranty for temperature
stipulations as some manufacturers will void the warranty if conditions where the
tank is installed can get extremely hot.
5
1.5.2 STEEL TANKS:
Steel tanks Galvanized tanks have been around for over 150 years and are
usually the cheapest type of tank. Hot-dip galvanizing is a process used to coat steel
or iron with zinc. The Zinc helps slow down corrosion, but depending on
environmental factors, a galvanized tank may last well under 5 years. This is due to
electrolysis. Some metal tanks now also have polyethylene linings to further help
retard corrosion - escaping plastic altogether can be a difficult thing to do these days.
With a steel based tank, seriously consider the composition of the water you are
storing and its potential to accelerate corrosion in any exposed metals.
1.5.3 FIBRE GLASS:
Fibre glass, this is another long-lasting option that can be installed above or
below ground. Fiberglass tanks resist corrosion and are not generally affected by
chemicals. As fiberglass tanks tend to allow more light in than other types of tank
materials, this can encourage the growth of algae, so they should be painted.
Fiberglass can also tend to be brittle, leaving it prone to cracks - something you don't
want, particularly in an in-ground situation.
1.5.4 CONCRETE TANK:
Concrete water storage tanks can be built above grade or mostly hidden from
view. They are built on site because of the material’s weight. Concrete is a porous
material and needs to be sealed to prevent minerals leaching into the water. With
proper sealing and construction techniques, this is can be addressed. Mining
production and delivery of concrete is energy intensive. The advantage is achieved
6
by its long life and its ability to be simply recycled. Choosing a tank material Choice
is wonderful, but as you can see, there are advantages and disadvantages with each
type of tank, particularly when it comes to environmental impact - so it's really a
matter of gagging your needs and budget and then choosing the lesser of the evils.
In regards to the financial side of things, bear in mind not just the initial cost, but
how many times the tank will need replacing over X years. This also plays a role in
the Concrete tanks have been used in rural areas for many years but are becoming
more common in the city, particularly pre-cast underground concrete tanks that can
be placed under driveways or front and back yards. The advantage of underground
concrete tanks is that they can collect large volumes of water in properties tight for
space that could not otherwise accommodate above-ground tanks. Houses with small
gardens still consume large volumes of water internally through laundries, toilets
and showers and could benefit from using underground concrete tanks for 'whole of
house' water supply.
1.6 ADVANTAGES OF CONCRETE WATER TANK
1.6.1 COST:
The actual concrete tank itself is generally only slightly more expensive than
some steel options, however it becomes more expensive per litre when placing
concrete tanks underground as excavation, transport and crane hire (for larger tanks)
can be quite expensive. However, with rising land and water prices it may be a wise
long-term investment for inner-city and small blocks, as an underground tank does
not take up any valuable space on the property. See the Price Comparison for price
estimates.
7
1.6.2 DETERIORATION/LIFESPAN/DURABILITY:
Concrete tanks are extremely durable and most purpose-built concrete
rainwater tanks have plasticizers added for strength and are poured into a seamless
mould to prevent leaks. Most manufacturers offer warranties of between 20 and 30
years, however a good quality concrete tank can last several decades. While not as
easy to repair as steel or fiberglass tanks, leaking concrete tanks can be fixed with
various sealants depending on the size of the crack and the position.
1.6.3 SIZE AND SHAPE:
There are more and more companies producing pre-cast concrete tanks in
many shapes and sizes including rectangular ones that fit neatly under driveways.
Underground concrete tanks can also be cast on site (in situ). Most concrete tanks,
whether pre-cast or built on site, are designed to be load bearing and are therefore
ideal for placing under driveways. Water quality: Some older concrete tanks may
leach lime, increasing the pH of water and affecting its taste. However, in most cases
the water quality from concrete tanks is very good. Concrete tanks tend to keep the
water cooler than most other tanks, reducing the likelihood of bacterial growth.
1.6.4 ENVIRONMENTAL CREDENTIALS:
Concrete tanks have high embodied energy; however a good quality concrete
tank will have a long life-span and can be recycled at the end of its life.
8
1.6.5 SITE PREPARATION:
Concrete tanks are extremely heavy and therefore some settling tends to
occur once put in place. The use of packing sand or cracker dust is recommended
and it may be worth rolling or compacting the sand before installing the tank to
reduce initial movement. It is advisable to allow the tank to settle for a
number of weeks before connecting fixed plumbing. Of resources used.
1.6.6 MERITS OF CONCRETE WATER TANK
• When rain water is stored it reduces its acidity.
• Concrete water tanks can with stand bush fire.
• Keeps water cool.
• Free from algae up to 100 years.
• Lasts longer.
1.6.7 DEMERITS OF CONCRETE WATER TANK
• Leakage
• Leaching
• Expensive
1.7 OBJECTIVES
The objective of this project is to plan and design a underground concrete
water tank for 2,00,000 liter capacity for Sri Shakthi institute of engineering and
technology.
9
CHAPTER 2
2. GENERAL DESIGN REQUIREMENTS OF CONCRETE (I.S.I)
Concrete Structures. Plain concrete member of reinforced concrete liquid
retaining structure may be designed against structural failure by allowing tension in
plain concrete as per the permissible limits for tension in bending. This will
automatically take care of failure due to cracking. However, nominal reinforcement
shall be provided, for plain concrete structural members. Permissible Stresses in
Concrete. (a) For resistance to cracking. For calculations relating to the resistance
of members to cracking, the permissible stresses in tension (direct and due to
bending) and shear shall confirm to the values specified in Table 2.1. The
permissible tensile stresses due to bending apply to the face of the member in contact
with the liquid. In members less than 225mm. thick and in contact with liquid on
one side these permissible stresses in bending apply also to the face remote from the
liquid.
(b) For strength calculations. In strength calculations the permissible concrete
stresses shall be in accordance with Table 2.1. Where the calculated shear stress in
concrete alone exceeds the permissible value, reinforcement acting in conjunction
with diagonal compression in the concrete shall be provided to take the whole of the
shear.
10
Table 2.1 Permissible concrete stresses in calculations relating to resistance to
cracking
Grade of concrete
Permissible stress in KN/m^2 tension
M15
Direct
Bending
1.1
1.5
shear
1.5
M20
1.2
1.7
1.7
M25
1.3
1.8
1.9
M30
1.5
2.0
2.2
M35
1.6
2.2
2.5
M40
1.7
2.4
2.7
11
Permissible Stresses in Steel (a) For resistance to cracking.
When steel and concrete are assumed to act together for checking the tensile
stress in concrete for avoidance of crack, the tensile stress in steel will be limited by
the requirement that the permissible tensile stress in the concrete is not exceeded so
the tensile stress in steel shall be equal to the product of modular ratio of steel and
concrete, and the corresponding allowable tensile stress in concrete.
(b) For strength calculations. In strength calculations the permissible stress shall
be as follows:
(i) Tensile stress in member in direct tension
(ii) Tensile stress in member in bending on liquid retaining face of members or face
away from liquid for members less than 225mm thick
(iii)On face away from liquid for members 225mm or more in thickness
(iv) Tensile stress in shear reinforcement, For members less than 225mm thickness
1000 kg/cm
1250 kg/cm
(v)Stresses due to drying shrinkage or temperature change may be ignored provided
that ñ The permissible stresses specified above in (ii) and (iii) are not otherwise
exceeded. Adequate precautions are taken to avoid cracking of concrete during the
construction period and until the reservoir is put into use. Recommendation
regarding joints given above and for suitable sliding layer beneath the reservoir are
complied with, or the reservoir is to be used only for the storage of water or aqueous
12
liquids at or near ambient temperature and the circumstances are such that the
concrete will never dry out.
(ii)Shrinkage stresses may however be required to be calculated in special
-6 cases, when a shrinkage co-efficient of 300 x 10 may be assumed.
(iii) When the shrinkage stresses are allowed, the permissible stresses, tensile
stresses to concrete (direct and bending) may be increased by 33.33 per cent.
2.1 DESIGN REQUIREMENT OF WATER TANK (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/m .
The design of the concrete mix shall be such that the resultant concrete is
sufficiently 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. All joints should be
made water-tight as these are potential sources of leakage.
Design of liquid retaining structure is different from ordinary R.C.C,
structures as it requires that concrete should not crack and hence tensile stresses in
concrete should be within permissible limits. A reinforced concrete member of
liquid retaining structure is designed on the usual principles ignoring tensile
resistance of concrete in bending. Additionally, it should be ensured that tensile
13
stress on the liquid retaining face of the equivalent concrete section does not exceed
the permissible tensile strength of concrete as given in table 1. For calculation
purposes the cover is also taken into concrete area.
Cracking may be caused due to restraint to shrinkage, expansion and
contraction of concrete due to temperature or shrinkage and swelling due to moisture
effects. Such restraint may be caused by ñ (i) The interaction between reinforcement
and concrete during shrinkage due to drying.
(ii) The boundary conditions.
(iii) The differential conditions prevailing through the large thickness of massive
concrete.
Use of small size bars placed properly, leads to closer cracks but of smaller
width. The risk of cracking due to temperature and shrinkage effects may be
minimized by limiting the changes in moisture content and temperature to which the
structure as a whole is subjected. The risk of cracking can also be minimized by
reducing the restraint on the free expansion of the structure with long walls or slab
founded at or below ground level, restraint can be minimized by the provision of a
sliding layer. This can be provided by founding the structure on a flat layer of
concrete with interposition of some material to break the bond and facilitate
movement.
In case length of structure is large it should be subdivided into suitable
lengths separated by movement joints, especially where sections are changed the
movement joints should be provided. Where structures have to store hot liquids,
stresses caused by difference in temperature between inside and outside of the
reservoir should be taken into account.
14
The coefficient of expansion due to temperature change is taken as 11 x -6 -6
10 / C and coefficient of shrinkage may be taken as 450 x 10 for initial
shrinkage and 200 x 10^-6for drying shrinkage.
2.2 JOINTS IN LIQUID RETAINING STRUCTURES
2.2.1 MOVEMENT JOINTS
There are three types of movement joints.
(i)Contraction Joint. It is a movement joint with deliberate discontinuity without
initial gap between the concrete on either side of the joint. The purpose of this joint
is to accommodate contraction of the concrete.
The joint is shown in Fig.1
Fig(2.1)
Figure (1) A contraction joint may be either complete contraction joint or partial
15
contraction joint. A complete contraction joint is one in which both steel and
concrete are interrupted and a partial contraction joint is one in which only the
concrete is interrupted, the reinforcing steel running through as shown in Fig (2.1).
(ii)Expansion Joint. It is a joint with complete discontinuity in both reinforcing steel
and concrete and it is to accommodate either expansion or contraction of the
structure. A typical expansion joint is shown in Fig (2.2)
Fig(2.2)
This type of joint requires the provision of an initial gap between the adjoining parts
of a structure which by closing or opening accommodates the expansion or
contraction of the structure.
(iii) Sliding Joint. It is a joint with complete discontinuity in both reinforcement
and concrete and with special provision to facilitate movement in plane of the joint.
A typical joint is shown in Fig (2.3). This type of joint is provided between wall and
floor in some cylindrical tank designs.
16
Fig (2.3).
2.2.2 CONTRACTION JOINTS
This type of joint is provided for convenience in construction. Arrangement
is made to achieve subsequent continuity without relative
Fig(2.4)
movement. One application of these joints is between successive lifts in a reservoir
wall. A typical joint is shown in Fig (2.4). The number of joints should be as small
as possible and these joints should be kept from possibility of percolation of water.
17
2.2.3 TEMPORARY JOINTS
A gap is sometimes left temporarily between the concrete of adjoining parts
of a structure which after a suitable interval and before the structure is put to use, is
filled with mortar or concrete completely as in Fig (2.5) with suitable jointing
materials. In the first case width of the gap should be sufficient to allow the sides to
be prepared before filling.
Fig (2.5).
Fig (2.6).
2.2.4 SPACING OF JOINTS
Fig(7).
Fig(8)
Unless alternative effective means are taken to avoid cracks by allowing for
the additional stresses that may be induced by temperature or shrinkage changes or
by unequal settlement, movement joints should be provided at the following spacing:
18
(a)In reinforced concrete floors, movement joints should be spaced at not more than
7.5m apart in two directions at right angles. The wall and floor joints should be in
line except where sliding joints occur at the base of the wall in which correspondence
is not so important.
(b)For floors with only nominal percentage of reinforcement (smaller than the
minimum specified) the concrete floor should be cast in panels with sides not more
than 4.5m. (c)In concrete walls, the movement joints should normally be placed at
a maximum spacing of 7.5m. in reinforced walls and 6m in unreinforced walls. The
maximum length desirable between vertical movement joints will depend upon the
tensile strength of the walls, and may be increased by suitable reinforcement. When
a sliding layer is placed at the foundation of a wall, the length of the wall that can be
kept free of cracks depends on the capacity of wall section to resist the friction
induced at the plane of sliding. Approximately the wall has to stand the effect of a
force at the place of sliding equal to weight of half the length of wall multiplied by
the co-efficient of friction.
(d)Amongst the movement joints in floors and walls as mentioned above expansion
joints should normally be provided at a spacing of not more than 30m between
successive expansion joints or between the end of the structure and the next
expansion joint; all other joints being of the construction type.
(e)When, however, the temperature changes to be accommodated are abnormal or
occur more frequently than usual as in the case of storage of warm liquids or in
uninsulated roof slabs, a smaller spacing than 30m should be adopted that is greater
proportion of movement joints should be of the expansion type). When the range of
temperature is small, for example, in certain covered structures, or where restraint is
small, for example, in certain elevated structures none of the movement joints
19
provided in small structures up to 45mlength need be of the expansion type. Where
sliding joints are provided between the walls and either the floor or roof, the
provision of movement joints in each element can be considered independently.
2.3 FLOORS
(i)Provision of movement joints.
Movement joints should be provided as discussed before.
(ii) Floors of tanks resting on ground.
If the tank is resting directly over ground, floor may be constructed of
concrete with nominal percentage of reinforcement provided that it is certain that the
ground will carry the load without appreciable subsidence in any part and that the
concrete floor is cast in panels with sides not more than 4.5m. with contraction or
expansion joints between. In such cases a screed or concrete layer less than 75mm
thick shall first be placed for members 225mm or more in thickness 1250 kg/cm
(v)Compressive stress in columns subjected to direct load 1250 kg/cm
Stresses due to drying Shrinkage or Temperature Change.
On the ground and covered with a sliding layer of bitumen paper or other
suitable material to destroy the bond between the screed and floor concrete. In
normal circumstances the screed layer shall be of grade not weaker than M 10, where
injurious soils or aggressive water are expected, the screed layer shall be of grade
not weaker than M 15 and if necessary a sulphate resisting or other special cement
should be used.
(iii) Floor of tanks resting on supports
20
If the tank is supported on walls or other similar supports the floor slab shall
be designed as floor in buildings for bending moments due to water load and self
weight. When the floor is rigidly connected to the walls (as is generally the case)
the bending moments at the junction between the walls and floors shall be taken into
account in the design of floor together with any direct forces transferred to the floor
from the walls or from the floor to the wall due to suspension of the floor from the
wall.
If the walls are non-monolithic with the floor slab, such as in cases, where
movement joints have been provided between the floor slabs and walls, the floor
shall be designed only for the vertical loads on the floor. In continuous T-beams and
L-beams with ribs on the side remote from the liquid, the tension in concrete on the
liquid side at the face of the supports shall not exceed the permissible stresses for
controlling cracks in concrete. The width of the slab shall be determined in usual
manner for calculation of the resistance to cracking of T-beam, L-beam sections at
supports.
The floor slab may be suitably tied to the walls by rods properly embedded
in both the slab and the walls. In such cases no separate beam (curved or straight) is
necessary under the wall, provided the wall of the tank itself is designed to act as a
beam over the supports under it. Sometimes it may be economical to provide the
floors of circular tanks, in the shape of dome. In such cases the dome shall be
designed for the vertical loads of the liquid over it and the ratio of its rise to its
diameter shall be so adjusted that the stresses in the dome are, as far as possible,
wholly compressive. The dome shall be supported at its bottom on the ring beam
which shall be designed for resultant circumferential tension in addition to vertical
loads.
21
2.4 WALLS
(i)Provision of joints
Where it is desired to allow the walls to expand or contract separately from
the floor, or to prevent moments at the base of the wall owing to fixity to the floor,
sliding joints may be employed.The spacing of vertical movement joints should be
as discussed above while the majority of these joints may be of the partial or
complete contraction type, sufficient joints of the expansion type should be provided
to satisfy the requirements given in article
(ii)Pressure on Walls.
In liquid retaining structures with fixed or floating covers the gas pressure
developed above liquid surface shall be added to the liquid pressure. When the wall
of liquid retaining structure is built in ground, or has earth embanked against it, the
effect of earth pressure shall be taken into account.
(iii) Walls or Tanks Rectangular or Polygonal in Plan.
While designing the walls of rectangular or polygonal concrete tanks, the
following points should be borne in mind. In plane walls, the liquid pressure is
resisted by both vertical and horizontal bending moments. An estimate should be
made of the proportion of the pressure resisted by bending moments in the vertical
and horizontal planes. The direct horizontal tension caused by the direct pull due to
water pressure on the end walls, should be added to that resulting from horizontal
bending moments. On liquid retaining faces, the tensile stresses due to the
combination of direct horizontal tension and bending action shall satisfy the
following condition:
22
(tí/t)+(Ûctí/Ûct )≤1 tí = calculated direct tensile stress in concrete
t = permissible direct tensile stress in concrete (Table 1) Û′ct = calculated tensile
stress due to bending in concrete. Ûct = permissible tensile stress due to bending in
concrete. At the vertical edges where the walls of a reservoir are rigidly joined,
horizontal reinforcement and haunch bars should be provided to resist the horizontal
bending moments even if the walls are designed to withstand the whole load as
vertical beams or cantilever without lateral supports. In the case of rectangular or
polygonal tanks, the side walls act as two- way slabs, whereby the wall is continued
or restrained in the horizontal direction, fixed or hinged at the bottom and hinged or
free at the top. The walls thus act as thin plates subjected triangular loading and with
boundary conditions varying between full restraint and free edge. The analysis of
moment and forces may be made on the basis of any recognized method.
(iv) Walls of Cylindrical Tanks.
While designing walls of cylindrical tanks the following points should be
borne in mind: Walls of cylindrical tanks are either cast monolithically with the base
or are set in grooves and key ways (movement joints). In either case deformation of
wall under influence of liquid pressure is restricted at and above the base.
Consequently, only part of the triangular hydrostatic load will be carried by ring
tension and part of the load at bottom will be supported by cantilever action. It is
difficult to restrict rotation or settlement of the base slab and it is advisable to provide
vertical reinforcement as if the walls were fully fixed at the base, in addition to the
reinforcement required to resist horizontal ring tension for hinged at base, conditions
of walls, unless the appropriate amount of fixity at the base is established by analysis
with due consideration to the dimensions of the base slab the type of joint between
the wall and slab, and , where applicable, the type of soil supporting the base slab.
23
2.5 ROOF
(i) Provision of Movement joints.
To avoid the possibility of sympathetic cracking it is important to ensure that
movement joints in the roof correspond with those in the walls, if roof and walls are
monolithic. However, provision is made by means of a sliding joint for movement
between the roof and the wall correspondence of joints is not so important.
(ii)Loading.
Field covers of liquid retaining structures should be designed for gravity
loads, such as the weight of roof slab, earth cover if any, live loads and mechanical
equipment. They should also be designed for upward load if the liquid retaining
structure is subjected to internal gas pressure. A superficial load sufficient to ensure
safety with the unequal intensity of loading which occurs during the placing of the
earth cover should be allowed for in designing roofs. The engineer should specify a
loading under these temporary conditions which should not be exceeded. In
designing the roof, allowance should be made for the temporary condition of some
spans loaded and other spans unloaded, even though in the final state the load may
be small and evenly distributed.
(iii)Water tightness.
In case of tanks intended for the storage of water for domestic purpose, the
roof must be made water-tight. This may be achieved by limiting the stresses as for
the rest of the tank, or by the use of the covering of the waterproof membrane or by
providing slopes to ensure adequate drainage.
24
(iv) Protection against corrosion.
Protection measure shall be provided to the underside of the roof to prevent
it from corrosion due to condensation.
2.6 MINIMUM REINFORCEMENT
The minimum reinforcement in walls, floors and roofs in each of two
directions at right angles shall have an area of 0.3 per cent of the concrete section in
that direction for sections up to 100mm, thickness. For sections of thickness greater
than 100mm, and less than 450mm the minimum reinforcement in each of the two
directions shall be linearly reduced from 0.3 percent for 100mm thick section to 0.2
percent for 450mm, thick sections. For sections of thickness greater than 450mm,
minimum reinforcement in each of the two directions shall be kept at 0.2 per cent.
In concrete sections of thickness 225mm or greater, two layers of reinforcement steel
shall be placed one near each face of the section to make up the minimum
reinforcement. In special circumstances floor slabs may be constructed with
percentage of reinforcement less than specified above. In no case the percentage of
reinforcement in any member be less than 0 15% of gross sectional area of the
member.
Minimum Cover to Reinforcement.
For liquid faces of parts of members either in contact with the liquid (such
as inner faces or roof slab) the minimum cover to all reinforcement should be 25mm
or the diameter of the main bar whichever is grater. In the presence of the sea water
and soils and water of corrosive characters the cover should be increased by 12mm
but this additional cover shall not be taken into account for design calculations.
For faces away from liquid and for parts of the structure neither in contact
25
with the liquid on any face, nor enclosing the space above the liquid, the cover shall
be as for ordinary concrete member.
2.7 FLEXIBLE BASE WATER TANK
For smaller capacities rectangular tanks are used and for bigger capacities
circular tanks are used. In circular tanks with flexible joint at the base tanks walls
are subjected to hydrostatic pressure .so the tank walls are designed as thin cylinder.
As the hoop tension gradually reduces to zero at top, the reinforcement is gradually
reduced to minimum reinforcement at top. The main reinforcement consists of
circular hoops. Vertical reinforcement equal to 0.3% of concrete are is provided and
hoop reinforcement is tied to this reinforcement.
2.8 RIGID BASE TANK
The design of rigid base circular tank can be done by the approximate
method. In this method it is assumed that some portion of the tank at base acts as
cantilever and thus some load at bottom are taken by the cantilever effect. Load in
the top portion is taken by the hoop tension. The cantilever effect will depend on the
dimension of the tank and the 2 thickness of the wall. For H /Dt between 6 to 12,
the cantilever portion 2 may be assumed at H/3 or 1m from base whichever is more.
For H /Dt between 6 to 12, the cantilever portion may be assumed at H/4 or 1m from
base whichever is more.
2.9 DESIGN REQUIREMENTS FOR UNDER GROUND WATER TANK
The tanks like purification tanks, Imhoff tanks, septic tanks, and gas holders
are built underground. The design principle of underground tank is same as for tanks
26
are subjected to internal water pressure and outside earth pressure. The base is
subjected to weight of water and soil pressure. These tanks may be covered at the
top. Whenever there is a possibility of water table to rise, soil becomes saturated and
earth pressure exerted by saturated soil should be taken into consideration. As the
ratio of the length of tank to its breadth is greater than 2, the long walls will be
designed as cantilevers and the top portion of the short walls will be designed as slab
supported by long walls. Bottom one meter of the short walls will be designed as
cantilever slab.
Comparative Study on the Design of Rectangular and Circular Concrete Water
Tanks
Structural Layouts:
The rectangular and circular walls were considered to be propped cantilevers.
Each of the propped cantilevers was made rigidly fixed to its base slab and was
expected to be drawn inward at the top by the wall/top slab connecting
reinforcements; in response to the outward hydrostatic loading on the wall. This was
put in view based on the fact that continuity reinforcement must be provided at
corners and at member-junctions to prevent cracking. The base slabs were typically
a double overhanging single-spanned continuous slab, with wall point load and its
applied fixed end moment at each overhang end. And the top slabs were laid out to
be either two-way spanning or simply supported as stated by Anchor. The tank
dimensions were deduced by the application of the related formula for solid shapes‟
volume calculations. Therefore, (L x B x H) for cuboid (or cube) was used for the
rectangular tank and (π x R2 x H) for cylinder was applied for the circular tank;
where L, B, H and R are Length, Breadth, Height and Radius respectively. For each
tank, the preliminary member sizing was done for the walls, base slab and top slab.
27
Water free-board was also provided for the possible volume increase above the
require capacity in order to limit or check the overflow of the tanks in accordance
with recommendations by BS 8007 (1987), and Reynolds and Steedman (1988). This
was practically allowed to ease the reinforcing and construction of joints.
Wall Loading:
The average water force or load, P in kN per meter width of the rectangular
tank walls under flexural tension was derived as a point or concentrated load by
calculating the areas of the triangular pressure diagrams of the water content on the
walls, to be (ρH) x H/2, where ρ is the water density. By the centroidal consideration
of loading of the pressure diagram, one-third distance from the base, up each wall,
was chosen as the point of application of the concentrated load. The circular tank
wall would be clearly in a state of simple hoop tension and its amount in kN per
meter height of wall would be (ρH) x D/2. And it would still act at one-third distance
from the base up each wall. The wall total working loads for both options were
assumed purely hydrostatic. And the inclusion of wind load in the working load was
purely made to be dependent on tank elevation above the ground level, but would
always be applicable in the design of its support. The wind load’s application point,
if considered, would be at one-half the tank’s height and acting against the lateral
water force. Hence, the resultant lateral force, from the combination of the water
force and wind force; if applicable, would be one-half way between the two forces,
that is, five-twelfth of the tank’s height. For the purpose of this study, tanks elevated
at 12 m and above were considered to be influenced by wind load.
Base Slab Loading:
For each of the water tank options, the base slab’s characteristic
serviceability uniformly distributed load in kN/m per m run, was the sum of its dead
28
load; the concrete self weight and its finishes, and its live load; that is, the weight of
water to be contained. And the serviceability point load in kN per meter run, acting
on each of the base slabs, at the extremes of the overhangs was derived by adding
up the wall dead load; i.e. the base projection’s weight and a calculated fraction of
the top slab load. But some noticeable difference might be experienced in the
calculations of the fractions of the loads from the rectangular and the circular top
slabs.
Top Slab Loading:
The top slab uniformly distributed load, in kN/m per meter run was
calculated by adding up its combined dead load; that is, concrete self weight,
waterproof finish and its live load (for tank access), to derive the characteristic
serviceability load. Factors of safety of 1.4 and 1.6 were applied to the combined
dead and live loads respectively before their sum was made to achieve the required
ultimate design load for the top slab. The ultimate requirement, that is, stability
would dictate its design and serviceability requirements; basically, deflection would
be checked (BS 8007, 1987)
Structural Analyses:
General: This entails the analyses of the loaded structural elements; walls,
base and top slabs in order to determine their bending moments for the required
design conditions. Serviceability loadings were considered for the general analysis
to concentrate on crack width and reinforcement tensile stress limit except for top
slab where this requirement would only be a check on the structural performance
through measure of deflection. The maximum bending moment from the support and
span for each condition was generally used and confirmed less than the moment of
29
resistance, Mu= 0.156 f bd 2 , where f is the 28-day concrete characteristic strength,
b is one meter width of slab and d is the effective slab depth (BS 8110, 2007).
30
CHAPTER 3
3.ANALYSIS AND DESIGN
3.1 DETERMINATION OF FIELD DENSITY OF SOIL BY CORE CUTTER
METHOD.
AIM:
To determine the field density of soil by core cutter method.
APPARATUS:
Ø Cylindrical core cutter.
Ø Steel rammer.
Ø Steel dally.
Ø Balance.
Ø Moisture content cups.
PROCEDURE:
Ø Measure the height (h) and internal diameter (d) of the core cutter and apply
grease to the inside of core cutter.
Ø Weigh the empty core cutter (w₁).
Ø Clean and level the place where density is to be determined.
Ø Drive the core cutter, with steel dally on its top into the soil to its full depth
with the help of a steel rammer.
Ø Excavate the soil around the cutter with a crow bar and gently lift the cutter
without disturbing the soil in it.
31
Ø Trim the top and bottom surface of the sample and clean the outside surface
of the water.
Ø Weigh the core cutter with soil (w₂).
Ø Remove the soil from the core cutter, using a sample ejector and take a
representative soil from it to determine the moisture content (w).
OBSERVATION:
Internal diameter of core cutter (D) =10cm
Height of the core cutter (h) =13cm
Volume of the core cutter (v) =1021.02cm²
Specific gravity of the core cutter (G) =2.738
Empty weight of the cylinder (w₁) =1.004 kg
Weight of the cylinder with soil (w₂) =4.570 kg
CALCULATION:
Field density=weight of soil
Volume
Volume=1021.02 cm²
Field density=4.570-1.004
1021.02
=3.493 g/cc
=34.93 KN/m.
32
3.2 FIXED FUNNEL TEST
AIM OF THE TEST:
To find the angle of repose of the soil sample.
MATERIALS REQUIRED:
Ø Soil sample
Ø funnel
PROCEDURE:
The material (sand) is poured through a funnel to form a cone .The tip of the
funnel should be held close to the growing cone and slowly raised as the pile
grows, to minimize the impact of falling particles. Stop pouring the material
when the pile reaches a predetermined height or the base a predetermined
width. Rather than attempt to measure the angle of the resulting cone directly,
divide the height by half the width of the base of the cone. The inverse tangent
of this ratio is the angle of repose.
FORMULA USED:
Tan ø=
Tan ø=
!""!#$%& #$(&
)(*)+&,% #$(&
(//1)
Ø=tan67 [
.
9
:
( )
]
33
CALCULATION:
Table3.1 Fixed funnel test
TRIAL
BASE(B)
HEIGHT(H)
ANGLE
OF
REPOSE
(ø)
1
11.5
4.2
36°8ʹ50ʺ
2
11.3
4.1
35°58ʹ00ʺ
3
10.8
4.3
38°31ʹ50ʺ
Finally by taking average the angle of repose is found to be 37° for the taken
soil sample.
Angle of repose=37°.
34
3.3. DESIGN OF RECTANGULAR UNDERGROUND WATER TANK
Capacity of water tank=200m3
Shape: Rectangular underground water tank
Unit weight of soil=34.93 KN/m3
Angle of internal friction φ=37°
Bearing capacity of soil = 230 KN/m2
Free board= .25 m
Materials available: M20 grade of concrete, Steel- Grade 1.
Characteristic Strengths
σcb=7 N/mm2
σst=140N/mm2
σctb=1.7 N/mm2
m=13, j=.84
DIMENSION CALCULATIONS
Required capacity= 200 m3
Assumed depth= 4 m
Total height with free board= 4.25 m
Area of tank in plane= 200 4= 50 m2
Use 10x5x4.25 m
CONDSIONS OF LOADING
L=10m, H=4.25m, B=5m
?
/
/
-
>2
=
;
A
C.1A
7@
A
= 2 (Long wall)
= 1.17 < 2 (Short wall)
35
?
-
=
7@
C.1A
= 2.35
Long wall span in one direction, Shot wall span in two directions.
Roof slab in one direction only.
ROOF SLAB ONE WAY
Assuming thickness of wall = 300 mm
Span of roof slab in the direction of bending =5.3 m
Live load=1.5 KN/m2
Self weight(200mm) =.2x1x1x24= 4.8 KN/m2
Screeding = 1 KN/m2
Total load (w)= 7.3 KN/m2
BENDING MOMENT(BM)
E
F.G
C
H
BM= xl2 =
x5.32 = 25.63 KN-m
DEPTH OF SLAB
BM= 8.7bd2
d=
1A.IG∗7@@@
.HF∗7@@@
= 1.71 m
de=175mm, d=200mm
36
Amount of reinforcement
At =25.63 ∗ 10^6 . 87 ∗ 140 ∗ 175 =1202 mm2
(At=
R
*(S#%
)
Provide 12mm dia bars at 100 mm c/c
Secondary reinforcement =
.7A
7@@
x 200 x 1000 = 300 mm2
Provide 6mm dia bars at 100 mm c/c
LONG WALL
?
-
=
7@
C.1A
= 2.35 > 2
Wall spans in vertical direction only, Walls are assumed fixed at the base
and supported at top.
Case(i) Tank full dry earth outside
Max water pressure = ww H = 10 x 4.25 =42.5 KN/m2
Max earth pressure = weH(
76TUV W
7XTUV W
)
76TUV GF
= 34.93x4.25(
7XTUV GF
)
=36.9 KN/m2
Net pressure on wall (P) = 42.5-36.9 = 5.6 KN/m2
37
Max negative BM (water face)
Mw =
Y- :
7A
=
A.I∗C.1A:
7A
= 6.74 KN-m
Max positive BM (Earth face)
Me =
Y- :
GG.A
=
A.I∗C.1A:
GG.A
= 3.01 KN-m
Case-(ii) Tank empty dry earth pressure outside
Max earth pressure = weH(
76TUV W
7XTUV W
)
76TUV GF
= 34.93x4.25(
7XTUV GF
)
=36.9 KN/m2
Max negative BM (water face)
Mw =
Y- :
7A
=
GI.Z∗C.1A:
7A
= 44.43 KN-m
Max positive BM (Earth face)
Me =
Y- :
GG.A
=
GI.Z∗C.1A:
GG.A
= 19.89 KN-m
Table.3.2 BM at water face and earth face.
Case
BM water face KN-m
BM earth face KN-m
1
6.74
3.01
2
19.89
44.43
38
Thickness of wall on cracking stress
Consideration
Resisting moment Mr =
[( : S+%[
I
7
44.43x106 = x1000xd2x1.7
I
d=395.99mm provide 400mm
de=400mm
d=440mm
REINFORCEMENT DETAILS FOR LONG WALL
Case(i) Tank full dry earth outside
At required for –ve BM
A t=
RE
S#% *(
=
I.IF∗7@\
7C@∗.HC∗C@@
= 141.79 mm2
Provide 12mm dia bars at 300 mm c/c
At required for +ve BM
A t=
R&
S#% *(
=
G.@7∗7@\
7C@∗.HC∗C@@
= 63.98 mm2
Provide 12 mm dia bars at 400 mm c/c
Case (ii) Tank empty dry earth outside
39
At required for –ve BM
A t=
RE
S#% *(
=
CC.CG∗7@\
7C@∗.HC∗C@@
= 944.5 mm2
Provide 12mm dia bars at 115 mm c/c
At required for +ve BM
A t=
R&
S#% *(
=
7Z.HZ∗7@\
7C@∗.HC∗C@@
= 422 mm2
Provide 12 mm dia bars at 250 mm c/c
Provide reinforcement details of Case(ii)
Secondary reinforcement
At =
.G
7@@
x 440 x 1000 = 1320 mm2
Provide 10mm dia bars at 60 mm c/c
SHORT WALL
BM VERTICAL DIRECTION
Case(i)
Mv=0.083wh2(
]
]X7
)
K=0.375 from the graph
Mv=0.083x5.6x4.252(
.GFA
.GFAX7
)=2.28KN/m
Max –ve moment (water face)=.89x2.28=2.0292KN/m
40
Max +ve moment(earth face)=.65x2.28=1.482KN/m
Case(ii)
Mv=0.083x36.9x4.252(
.GFA
.GFAX7
)=15.09KN/m
Max –ve moment (water face) =.89x15.09=13.43KN/m
Max +ve moment (earth face) =.65x15.09=9.808KN/m
BM HORIZONTAL DIRECTION
Case(i)
Mh=
Mh=
.@IF∗E- :
(^X7)
.@IF∗A.I∗C.1A:
(.GFAX7)
= 6.82 KN/m
-ve moment at corner (water face) =.57Mh=.57x6.82=3.88KN-m
+ve moment at center (earth face)=.43Mh=.43x6.82=2.93KN-m
Case(ii)
Mh=
Mh=
.@IF∗E- :
(^X7)
.@IF∗GI.Z∗C.1A:
(.GFAX7)
= 44.95KN/m
-ve moment at corner (water face) =.57Mh=.57x44.95=25.62KN-m
41
+ve moment at center (earth face)=.43Mh=.43x44.95=19.32KN-m
DIRECT TENSION IN SHORT WALL
p=42.5KN/m
TB =
C1.A∗7
1
=21.25KN
Maximum moment in short wall occurs in Case (ii)
Thickness of the side wall
7
I
∗ _` 1 abc_=25.62x106 N/mm2
d2 =
1A.I1∗7@\ ∗I
7@@@∗7.F
d=300.7 mm
How ever use the same thickness as the long wall that is
de=400mm
d=440mm
MAIN REINFORCEMENT FOR THE SHORT WALL
Steel required for Max bending moment at corner (water face )
At =
1A.I1∗7@\
7C@∗.HC∗C@@
= 544.64 mm2
Provide 12 mm dia bars at 200 mm c/c
Steel required for Max bending moment at center (earth face )
42
At =
7Z.G1∗7@\
7C@∗.HC∗C@@
= 410.7 mm2
Provide 10 mm dia bars at 160 mm c/c
Secondary reinforcement
A t=
@.G
7@@
x440x1000=1320mm2
Provide 10mm dia bars at 60 mm c/c
BASE SLAB
d 10
=
=2
e
5
Spans in one direction only
Case(i)Tank full and dry soil outside
In this case the water pressure on base slab will be concentrated by the soil
pressure below it.
Loads
Weight of the roof = 24x5.88x10.88=1535.38KN
Weight of side walls=2x(10.44+5.44)x4.25x24x.44=1425.38KN
Total weight =1535.38+1425.38=2960.76KN
Base slab dimensions =6.88x11.88
Soil reaction below base=
1ZI@.FI
I.HH∗77.HH
43
=36.33KN/m
I.HH
BM at center of the slab(water face)=36.22x
1
x(
A.CC
1
–
I.HH
C
)
=124.59KN/m
GI.GG∗@.F1
BM at support(earth face)=
1
=13.03KN/m
Case(i)
-ve BM at base due to loads on the side wall (water face )=19.89KM-m
Net max BM at center (produces tension on the water face) = 124.59+6.74
=131.33KN-m
Net Max BM at support (produces tension on the water face) =13.03-6.74
=6.29KN-m
Case(ii) Tank empty dry soil outside
BM due to Self weight of roof and side walls and center(water
face)=124.59KN-m
At support=13.03KN-m
BM at the base due to soil pressure (earth face) =44.43KN-m
Net moment at center of the slab (Produces the tension on the outer face)
=124.59-44.43=80.16KN-m
Net BM at the support =44.43+13.03=57.46KN-m
44
Table 3.3 BM at center and at supports
Case
BM at center
BM at support
1
131.33KN-m
6.29KN-m
2
80.16KN-m
57.46KN-m
Thickness of the slab on cracking stress consideration
7
I
xbxd2xσctb=131.33
d=
7G7.GG∗I
7@@@∗7.F
=463.51mm
de=470mm ; d=520mm
Main reinforcement
Case(i)
A t=
7G7.GG∗7@\
7C@∗.HC∗CF@
= 2376.06 mm2
Use 16 mm dia bars at 80 mm c/c steel at support (water face)
A t=
I.1Z∗7@\
7C@∗@.HC∗CF@
=113.8 mm2
Use 16mm dia bars at 100 mm c/c
Case(ii)
A t=
AF.CI∗7@\
7C@∗.HC∗CF@
= 1039.58 mm2
45
Use 10 mm dia bars at 80 mm c/c
Secondary reinforcement
At=0.2% of cross sectional area (d>450mm)
A t=
@.1
7@@
x520x1000 = 1040 mm2
Use 10 mm dia at 150 mm c/c.
46
Fig(3.1)Reinforcement details of plan
47
Fig(3.2)Reinforcement details of long wall and short wall
48
CHAPTER 4
4. CONCLUSION
Thus rectangular underground water tank with a capacity of 2,00,000
liters is planned, designed, and manually analyzed for Sri Shakthi Institute of
Engineering and technology. In this project we analyzed all materials behavior
that are used for water storage and found that concrete tanks can be effectively
used for water storage. The other details of reinforcement used, Concrete
mixture, Symbols used, Tables, Diagrams and plan are shown in the project.
This project helped us to gain sufficient knowledge about the planning,
Design and analyze of rectangular underground concrete water tanks.
49
CHAPTER 5
5.REFERENCE
• Dayaratnam P. Design of Reinforced Concrete Structures. New Delhi.
Oxford & IBH publication.2000
• Vazirani & Ratwani. Concrete Structures. New Delhi. Khanna
Publishers.1990.
• Sayal & Goel. Reinforced Concrete Structures. New Delhi. S. Chand
publication.2004.
• D.Krishnamurthy, Structural Design and Drawing (volume 2) .
• IS 456-2000 CODE FOR PLAIN AND REINFORCED CONCRETE
• IS 3370-1965 CODE FOR CONCRETE STRUCTURES FOR HE
STORAGE OF LIQUIDS
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