DESIGN OF ELEVATED SERVICE RESERVOIR
1.0 INTRODUCTION :
For storage of large quantities of liquids like water, oil, petroleum, acid
and sometime gases also, containers or tanks are required. These structures are
made of masonry, steel, reinforced concrete and pre stressed concrete.
Out of these, masonry and steel tanks are used for smaller capacities. The
cost of steel tanks is high and hence they are rarely used for water storages.
Reinforced concrete tanks are very popular because, besides the construction and
design being simple, they are cheap, monolithic in nature and can be made leak
proof.
Generally no cracks are allowed to take place in any part of the structure of
Liquid Retaining R-C.C. tanks and they are made water tight by using richer mix
(not less than M 30) of concrete. In addition some times water proofing materials
also are used to make tanks water tight.
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1.1) CLASSIFICATION OF R.C.C. TANKS :
In general they are classified in three categories depending on the situation.
1. Tanks resting on ground.
2. Tanks above ground level (Elevated tanks).
3. Under ground tanks.
1.2. TANKS RESTING ON GROUND:
These are used for clear water reservoirs, settling tanks, aeration tanks etc.
these tanks directly rest on the ground. The wall of these tanks are subjected to
water pressure from inside and the base is subjected to weight of water from inside
and soil reaction from underneath the base. The tank my be open at top or roofed.
Ground water tank is made of lined carbon steel, it may receive water from a water
well or from surface water allowing a large volume of water to be placed in
inventory and used during peak demand cycles.
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FIG NO 1.1: . TANKS RESTING ON GROUND
1.3.ELEVATED TANKS: These tanks are supported on staging which may
consist of masonry walls, R.C.C tower or R.C.C. column braced together- The
walls are subjected to water pressure from inside. The base is subjected to weight
of water, wt- of walls and wt. roof. The staging has to carry load of entire tank
with water and is also subjected to wind loads.
Water tank parameters include the general design of the tank, choice of materials
of construction, as well as the following.
1. Location of the water tank (indoors, outdoors, above ground or underground)
determines color and construction characteristics.
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2. Volume of water tank will need to hold to meet design requirements.
3. Purpose for which the water will be used, human consumption or industrial
determines concerns for materials that do not have side effects for humans.
4. Temperature of area where water will be stored , may create concern for freezing
and delivery of off setting heat.
5. Delivery pressure requirements, domestic pressures range from 35-60 PSI, the
demand for a given GPM (gallons per minute) of delivered flow requirements.
6. How is the water to be delivered to the point of use, into and out of the water
tank i.e. pumps, gravity or reservoir.
7. Wind and Earthquake design considerations allow a design of water tank
parameters to survive seismic and high wind events.
8. Back flow prevention, are check valve mechanisms to allow single direction of
water flow.
9. Chemical injection systems for algae, bacteria and virus control to allow long
term storage of water.
10. Algae in water tanks can be mitigated by removing sunlight from access to the
water being stored.
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