Overhead water tanks for residential homes are essential because they provide a continuous water supply 24 hours a day, seven days a week, to be used in drinking, cooking, and gardening, as well as car washing and clothes washing.
Concrete water tanks can be made in different shapes, such as rectangular or circular.
The main components of concrete water tanks are reinforced cement concrete (RCC), ferrocement (ferrocene), piers, or any other materials that have sufficient strength to withstand both the weight of water and the tank, as well as uplift forces resulting from an overturn.
IS 3370:2009 (Parts I-IV) is used to create the design of concrete water tanks. The method of concrete water storage tanks varies depending on where they are located, i.e., Overhead, underground, or groundwater tanks.
The Basics of Concrete Water Tank Design
- The plain section should be clear after turning.
- Concrete and steel must be elastic, and the modular ratio should have a value that is specified in IS 456-Table 21.
- When computing stresses for both flexural tension and direct tension, or a combination of the two, in relation to resistance to cracking, the entire section of concrete, along with the cover, as well as the reinforcement.
- It is not necessary to include the concrete’s tensile strength in the calculation of power.
Allowable stress on concrete to resist cracking
The water tank should be leak-proof. Concrete of M20 grade or higher should be used for this purpose. The concrete around the water face should also be designed so that it does not crack. Water walls should be designed so that they put less stress on concrete.
These allowable stresses for bending also apply to the side that is not in contact with the liquid.
Maximum Allowable Stress in Steel
To prevent concrete cracking, the stress in steel should never exceed these values.
- If steel is placed adjacent to the faces of the members that are in contact with liquid, 115 N/mm2 will be applied for mild steel bars, and 150 N/mm2 will be used for high-strength deformed bars.
- If the steel bar is positioned on the surface away from the liquid, and the member has a thickness of 225mm or greater, the maximum allowable steel stress should be 125N/mm2. This value increases to 190N/mm2 when the steel bar is high strength deformed.
- The same as the former, if steel is provided on the face away from liquid for members less than 225mm in thickness.
Floors of Reinforced Concrete Water Tank
Movement joints
IS 3770, Part I: Movement joints must comply with IS 3770
Base Of Tanks Rest On Support
- It should be designed to withstand bending moments caused by dead loads and water loads.
- When designing the floor for a multi-cell water storage tank, it is important to pay attention.
- When the floor and walls are firmly attached, the moment at the intersection, as well as other transferred loads, must be considered in the floor design.
Concrete Water Tank Walls
Joints
The following situations are suitable for sliding joints:
- If the wall is to be extended or contracted discreetly from the floor.
- The floor is fixed to the wall, so it will resist any moments that may occur at the base.
RCC Water Tank Roof
- If you want to avoid sympathetic cracking in your walls and roof, ensure that the movement joints on the top are the same as those in the walls.
- The roof of the tank should be water-resistant when it is being used to store water for domestic purposes.
- You can achieve this by either applying the waterproof membrane to the entire tank or creating slopes that retain enough drainage.
Minimum reinforcement required for RCC water tanks
- The minimum support for sections 199 mm thick should be 0.3 percent of the concrete area. This decreases linearly to 0.2% of the substantial team for branches with a 450 mm thickness.
- The minimum reinforcement for the floor slab of a tank situated on the ground should not be less than 0.3% gross sectional area.
- Two layers of steel reinforcement should be placed near each section of the tank if the thickness is less than 225 mm.