How to calculate wind loads from wind speeds

Written by finn mccuhil
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How to calculate wind loads from wind speeds
Wind load depends on wind speed and the size and shape of the surface area. (wind image by hanna kreis from Fotolia.com)

Wind load is a determination of the amount of stress a structure experiences at a given wind speed. This calculation is important when determining the height of a building, antenna or even the mast on a sailboat. Determining actual wind load for even a simple structure is a complex process and should be done by a design engineer. The generic formula given below should be used only for rough estimates, not for final building designs. If you are building a tall structure, consult an engineer for accurate calculations. Contact a marine architect if you are designing a sailboat.

Skill level:
Easy

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Instructions

  1. 1

    Calculate the force exerted by the wind at your target speed by squaring the speed in miles per hour and multiplying the answer by .00256.

    For a 30mph wind the calculation would be

    30 * 30 * .00256 = 2.304.

    This is the amount of pressure, per square foot, a 30mph wind exerts.

  2. 2

    Multiply the force determined Step 1 by the structure's surface area. With a 30mph wind and a structure with a surface area of 100 square-feet, the calculation is

    2.304 * 100 = 230.4.

  3. 3

    Multiply your answer from Step 2 by the structure's drag coefficient. For a flat square structure, multiply by 2.0. For a rounded structure, use 1.2.

    For flat structure with a surface area of 100 square feet, a 30mph wind would create a wind load of

    230.4 * 2.0 = 209 Kilogram.

Tips and warnings

  • The generic formula for calculating wind loads is as follows:
  • Force = Area * Pressure (per square foot) * Drag Coefficient.
  • In the calculations above, the asterisk is used to represent the multiplication sign.
  • This calculation determines the load on the surfaces of the structure facing into the wind only. It does not include turbulence, lift, vibration or any of the other numerous factors needed for exact structural requirements. More detailed calculations are available in the resources link.

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