DESIGN OF R.C.C. OVER HEAD TANK MAIN PROJECT REPORT
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Storage reservoirs and overhead tank are used to store water, liquid
petroleum, petroleum products and similar liquids. The force analysis of the
reservoirs or tanks is about the same irrespective of the chemical nature of
the product. All tanks are designed as crack free structures to eliminate any
This project gives in brief, the theory behind the design of liquid retaining
structure (Elevated circular water tank with domed roof and conical base)
using working stress method. Elements are design in limit state method.
A water tank is used to store water to tide over the daily requirement. In the
construction of concrete structure for the storage of water and other liquids
the imperviousness of concrete is most essential .The permeability of any
uniform and thoroughly compacted concrete of given mix proportions is
mainly dependent on water cement ratio .The increase in water cement ratio
results in increase in the permeability .The decrease in water cement ratio
will therefore be desirable to decrease the permeability, but very much
reduced water cement ratio may cause compaction difficulties and prove to
be harmful also. Design of liquid retaining structure has to be based on the
avoidance of cracking in the concrete having regard to its tensile strength.
Cracks can be prevented by avoiding the use of thick timber shuttering
which prevent the easy escape of heat of hydration from the concrete mass
.the risk of cracking can also be minimized by reducing the restraints on
free expansion or contraction of the structure.
Design Periods & Population Forecast
This quantity should be worked out with due provision for the estimated requirements of
the future. The future period for which a provision is made in the water supply scheme is
known as the design period.
Design period is estimated based on the following:
• Useful life of the component , considering obsolescence, wear, tear, etc.
• Expandability aspect.
• Anticipated rate of growth of population, including industrial, commercial
developments & migration-immigration.
• Available resources.
• Performance of the system during initial period.
Population Forecasting Methods
The various methods adopted for estimating future populations are given below. The
particular method to be adopted for a particular case or for a particular city depends
largely on the factors discussed in the methods, and the selection is left to the discrection
and intelligence of the designer.
1. Incremental Increase Method
2. Decreasing Rate of Growth Method
3. Simple Graphical Method
4. Comparative Graphical Method
5. Ratio Method
6. Logistic Curve Method
7. Arithmetic Increase Method
8. Geometric Increase Method.
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 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 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.
Minimum Cover to Reinforcement.
(a)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.
(b)For faces away from liquid and for parts of the structure neither in contact with the
liquid on any face, nor enclosing the space above the liquid, the cover shall be as for
ordinary concrete member.
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
Storage of water in the form of tanks for drinking and washing purposes,
swimming pools for exercise and enjoyment, and sewage sedimentation
tanks are gaining increasing importance in the present day life. For small
capacities we go for rectangular water tanks while for bigger capacities
we provide circular water tanks.
Design of water tank is a very tedious method. With out power also we can
consume water by gravitational force.