Designing an overhead rectangular water tank involves several steps, including determining the capacity, selecting materials, and ensuring structural stability. Here's a step-by-step guide to help you through the process:

1. Determine the Capacity

• Usage estimation: Calculate the daily water requirement and decide on the number of days of storage needed.

• Formula: Volume (V) = Length (L) × Width (W) × Height (H)

• Example: For a tank to hold 10,000 liters, V = 10 cubic meters (since 1 cubic meter = 1,000 liters).

2. Select the Dimensions

• Length, Width, Height: Choose dimensions that fit your available space and desired aesthetic. Ensure the dimensions maintain structural stability.

• Example: For 10 cubic meters, you could choose L = 2.5m, W = 2m, H = 2m (since 2.5 × 2 × 2 = 10 cubic meters).

3. Material Selection

• Common materials: Reinforced concrete, steel, or plastic (polyethylene).

• Considerations: Durability, cost, ease of construction, and maintenance.

4. Structural Design

• Walls and Base: Must withstand the hydrostatic pressure of the water.

• Thickness calculation: Depends on material strength and height of the tank.

• Reinforcement: Typically requires steel bars in reinforced concrete tanks.

• Roof Design: Should prevent contamination and evaporation, may also need reinforcement.

• Foundation: Must support the weight of the tank when full. Consider soil bearing capacity.

5. Hydraulic Design

• Inlet and Outlet: Design for efficient filling and drainage.

• Overflow pipe: Prevents overflow and directs excess water away safely.

• Ventilation: Prevents vacuum and allows air movement.

6. Additional Considerations

• Access: Provide manholes for inspection and maintenance.

• Ladders and Railings: For safe access.

• Waterproofing: Especially important for concrete tanks.

• Insulation: If temperature control is necessary.

  
  

Example Design

Let's design a concrete water tank with a capacity of 10,000 liters.

Capacity: 10 cubic meters (10,000 liters)

Dimensions:

• Length (L): 2.5 meters

• Width (W): 2 meters

• Height (H): 2 meters

Material: Reinforced concrete

Wall Thickness:

• Based on standard practices, a wall thickness of 150 mm (0.15 meters) is often used for small tanks. However, structural analysis is required for precise thickness.

Reinforcement:

• Use steel bars (rebar) as per design requirements. For a tank of this size, rebars of 10-12 mm diameter spaced at 150-200 mm are typically used.

Foundation:

• Ensure the foundation is strong enough to support the tank's weight (concrete slab of adequate thickness, typically around 200 mm, depending on soil conditions).

Hydraulic Design:

• Inlet pipe: Position at the top of the tank.

• Outlet pipe: Near the bottom for maximum usage.

• Overflow pipe: Near the top to handle excess water.

• Ventilation: Include a vent with a mesh cover to prevent debris entry.

Safety Features:

• Manhole: For inspection and maintenance, with a secure cover.

• Ladders and Railings: For safe access to the top of the tank.

Structural Analysis

A detailed structural analysis should be performed by a civil or structural engineer to ensure the tank can withstand the loads, including:

• Water pressure: Varies with depth; highest at the base.

• Dead load: Weight of the tank itself.

• Live load: Any additional loads, such as people accessing the top for maintenance.

• Wind load: If the tank is exposed to strong winds.

• Seismic load: If located in an earthquake-prone area.

By following these steps and ensuring proper design and construction practices, you can create a durable and efficient overhead rectangular water tank.