Reinforced Concrete Water Tank - Design Considerations - IS 3370

Reinforced Concrete Water Tanks are constructed mainly in three types. They are: 

1. Underground Tanks 
2. Elevated Tanks 
3. Tanks over the ground 

The Elevated tanks are supported by properly designed staging.

The codes that are used for water tank design is IS: 3370. The different parts of the code is mentioned along with the respective sections dealt.

Connections

The main connection that is concerned in the water tank design is between the water tan walls and the bottom floors. The joint provided here can be of three types. They are:

1. Fixed Joint 
2. Hinged Joint 
3. Free Base or a Flexible Joint 

The joint details are mentioned in the code IS:3370 -Part IV. Based on the base implemented the design calculations will change.

A fixed base and a hinged base have a restrain action which will result in moments and tension that have to be calculated.

• This will require Moment coefficient and ring tension at the base. Non-dimensional parameters can be used to express the moment coefficients.

            The parameter is: H2/ Dt

Here H = Height of the Tank
D = Diameter of the Tank
t = thickness of the tank wall

A free base between the walls and the base will not bring any restrain reactions or moments which will require only the determination of the hoop tension that is created due to hydrostatic pressure.

Special Considerations

The important considerations in the design of water tank is as per IS: 3370-2009 (Part - II).

1. Richer Mix are employed - M20 & M30 
2. High Water Tightness have to be provided 
3. The bending and tension stress value is kept within the permissible value in order to prevent cracking. As per Table. 1 

1. The permissible stress in steel is as per Table.4 

Main Types of Water Tank

Other than the three types of tank explained, classification based on cross - section is:

1. Circular Water Tank 
2. Rectangular Water Tank 
3. Intze Type Water Tank