Design of water tank

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Water tanks are storage containers of water; these tanks are usually storing water for human consumption. The need for water tanks is old as civilized man. Water tanks provide for the storage of drinking water potable, irrigation,agriculture, fire suppression, agricultural farming and live stoke, chemical manufacturing, food preparation and many other applications. Various materials are used for constructing water tanks; plastic, polyethylene, polypropylene, fiberglass, and concrete, steel (welded or bolted, carbon or stainless).

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The design of water tank is dictated by these variables

  1. Location of the water tank (indoors, outdoors, above ground or underground)
  2. Volume of water tank need to hold
  3. What the water will be used for
  4. Temperature of area where will be stored, concern for freezing
  5. Pressure required delivering water
  6. How the water to be delivers to the water tank


In general there are three kinds of water tanks:

  • Resting on the ground level
  • Underground tanks
  • Elevated tanks
  • From design point of view the tanks may be classified as per shape

    1. Circular tanks
    2. Square tanks
    3. Rectangular tanks
    4. Intze tanks
    5. Spherical tanks
    6. Conical bottom tanks
    7. Polygon water tanks
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    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.

    The code book used for water tank design is based on IS 3370: 2009 (Parts I – IV). The design depends on the location of tanks, i.e. overhead, on ground or underground water tanks.

    Design Methods

    Working stress method of design, considered as the method of earlier times, has several limitations. However, in situations where limit state method cannot be conveniently applied, working stress method can be employed as an alternative. It is expected that in the near future the working stress method will be completely replaced by the limit state method. Though the choice of the method of design is still left to the designer as per cl.18.2 of IS 456:2000.Limited cracking width in the liquid retaining structure designed by working stress method was the main reason why the Indian Standard IS: 3370 (1965) did not adopt the limit state design method even after adoption by IS;456 – 1978. However, IS:3370 adopted limit state design method in 2009 with the following advantages - limit state design method considers the materials according to their properties , treats load according to their nature , the structures also fails mostly under limit state and not inelastic state and limit state method also checks for serviceability.IS:3370-2009 adopts limit state design method with precautions. It adopts the criteria for limiting crack width when the structures are designed by considering ultimate limit state and restricts the stresses to 130 MPa in steel so that cracking width is not exceeded this is considered to be deemed to be satisfy condition. This precaution ensures cracking width to be less than 0.2 mm i.e. fit for liquid storage. This also specifies clearly how a liquid storage structure differs with other structures. A thorough study through both the versions of IS:3370 reveals the following four methods of designs:

    1. Working stress method in accordance IS 3370 (1965)
    2. Working stress method in accordance IS 3370 (2009)
    3. Designing by Ultimate Limit State and then checking cracking width by limit state of serviceability IS 3370 (2009)
    4. Limit state design method by limiting steel stresses
    5. Software used for design and analysis

      STAAD PRO, SAP 2000

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