How to Calculate Projected Area for Wind Loads

Written by william hirsch
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The force of the wind blowing against a structure causes a load. A load is a weight or force applied to specific surface. On a building for example, the area of the side of an awning would be subjected to a wind load. The surface area of the side of an object that is hit by the wind is known as the projected area. Calculate the projected area of the surface based on its shape.

Skill level:
Moderate

• Ribbon
• Tape measure
• Calculator

Rectangular Area

1. 1

Determine the direction of the wind by holding up a small piece of ribbon. The direction the ribbon blows is the wind direction.

2. 2

Measure the length and width of the surface facing the wind in inches. For example, the dimensions might include a length of 40 inches and a width of 30 inches.

3. 3

Convert the measurements to feet by dividing by 12. Continuing the exercise, you have now a length of 3.3 feet and a width of 2.5 feet.

4. 4

Multiply the length by the width to obtain the projected area for the wind load in square feet. Completing the exercise leads to 3.3 feet times 2.5 feet which equals an area of 8.3 square feet.

Circular Area

1. 1

Find the direction of the wind by watching the way a ribbon blows in your hand.

2. 2

Measure the radius of the projected circle in inches. Radius measures the distance from the centre of the circle to its edge. Suppose the radius is 18 inches.

3. 3

Convert the radius to feet by dividing by 12, since a foot contains 12 inches. Now the radius is 1.5 feet.

4. 4

Multiply the number pi times the square of the radius to get the projected area in square feet. Use 3.14 for pi. Completing the exercise yields 3.14 times 1.5 feet times 1.5 feet, or an area of 7.1 square feet.

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