Design of Retaining Water Structure: Volume and Material Requirements

Design of Retaining Water Structure: Volume and Material Requirements

Water retaining structures like tanks, reservoirs, and dams are used to control water supply planned for irrigation use, household consumers, and industries. Designing such structures requires proper estimation of the volume of water they are supposed to hold in addition to estimating the materials to be used in constructing it to enhance durability, stability, and waterproofness.

In this article, we will discuss the general design stages to compute the volume of water-retaining structures and material requirements for construction.

Basic Considerations in Designing a Water Retaining Structure
While designing a water retaining structure, the following considerations are essential:

·         Capacity Requirement : The amount of water that the structure requires to hold

·         Structural Integrity: Its ability to resist hydrostatic pressure forces that occur with held water.

·         Material Durability: Water resistance and environmental durability.

·         Waterproofing Measures: Prevent leakage and ensure long durability.

The size of the structure can run from a small water tank to large reservoirs and dams, but the principles of designing are pretty much consistent.

Step 1: Volume Calculation of Water Retaining Structures

To calculate the volume of a water retaining structure, the formula depends on the shape of the structure. Below are some common types of structures:

1. Rectangular Water Tank

For a rectangular water tank, the volume (V) is calculated using the formula:

V = L × W × H

Where:

• L = Length of the tank
• W = Width of the tank
• H = Height of the tank

Example:

Assume we are designing a rectangular water tank with dimensions:

• Length = 10 meters
• Width = 5 meters
• Height = 4 meters

The volume will be:

V = 10 × 5 × 4 = 200 m³

So, the tank can hold 200 cubic meters of water.

2. Circular Water Tank

For a cylindrical (circular) water tank, the volume (V) is calculated using the formula:

V = π × r² × H

Where:

• r = Radius of the tank
• H = Height of the tank

Example:

Assume a circular water tank with a radius of 3 meters and a height of 6 meters.

The volume will be:

V = 3.1416 × (3)² × 6 = 3.1416 × 9 × 6 = 169.65 m³

So, the circular tank can hold approximately 169.65 cubic meters of water.

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Step 2: Material Requirements for Water Retaining Structures

After determining the volume of the structure, we calculate the material requirements. The main materials for a water retaining structure are typically concrete, steel reinforcement, and waterproofing materials.

Concrete Quantity Calculation

The amount of concrete required depends on the thickness of the structure’s walls, base, and roof. The general formula for calculating the volume of concrete is:

Concrete Volume = Surface Area × Thickness

Let’s break it down by calculating for the walls, base, and roof.

1. Wall Concrete Calculation (Rectangular Tank)

For a rectangular tank, let’s assume the wall thickness is 0.3 meters. The surface area of the walls is calculated by adding the areas of all four walls.

Wall Surface Area = 2 × (L × H) + 2 × (W × H)

Using the dimensions from our rectangular tank example (L = 10 m, W = 5 m, H = 4 m):

Wall Surface Area = 2 × (10 × 4) + 2 × (5 × 4) = 2 × 40 + 2 × 20 = 80 + 40 = 120 m²

Now, the volume of concrete for the walls is:

Wall Concrete Volume = 120 m² × 0.3 m = 36 m³

2. Base Concrete Calculation

The surface area of the base is simply the area of the base of the tank:

Base Area = L × W = 10 × 5 = 50 m²

Assuming the base thickness is also 0.3 meters, the base concrete volume is:

Base Concrete Volume = 50 m² × 0.3 m = 15 m³

3. Roof Concrete Calculation (If Required)

If the tank has a roof, the roof’s surface area would be the same as the base:

Roof Area = L × W = 10 × 5 = 50 m²

Assuming the roof thickness is 0.15 meters, the concrete volume for the roof is:

Roof Concrete Volume = 50 m² × 0.15 m = 7.5 m³

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Step 3: Steel Reinforcement Calculation

Steel reinforcement is essential for ensuring the structural integrity of the tank. The amount of steel is usually expressed as a percentage of the concrete volume, based on the design specifications. Typically, 1%–2% of the concrete volume is used as steel reinforcement.

Example:

For the walls, we calculated 36 m³ of concrete. Let’s assume 1.5% steel reinforcement is required.

Steel Reinforcement = 36 m³ × 1.5 / 100 = 0.54 m³

Convert this volume into weight (density of steel = 7850 kg/m³):

Steel Weight = 0.54 m³ × 7850 kg/m³ = 4,239 kg

So, approximately 4,239 kg of steel reinforcement will be required for the walls.

Similar calculations can be done for the base and roof.

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Step 4: Waterproofing Material Calculation

Waterproofing is crucial to prevent water leakage. Materials like bitumen sheets, membranes, or waterproof concrete additives are commonly used.

The surface area of the interior of the tank needs to be covered. For a rectangular tank, the interior surface area is the sum of the areas of the walls, base, and roof:

Total Interior Surface Area = Wall Surface Area + Base Area + Roof Area

From the previous calculations, we have:

• Wall Surface Area = 120 m²
• Base Area = 50 m²
• Roof Area = 50 m²

Total Interior Surface Area = 120 + 50 + 50 = 220 m²

You would need enough waterproofing material to cover 220 m² of surface area.

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Conclusion

Designing water-retaining structures requires accurate volume calculations and estimating the quantities of material for construction. In this way, the structure can both be functional and durable, exerting tremendous pressure due to water it contains. Following these calculations you may design efficient and reliable tanks or reservoirs using the article.