How to calculate windload on permeable fence
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When wind hits a solid fence, it is diverted over and around the fence. A concrete block wall is an example of a solid fence. When wind hits a permeable fence, it can go through the fence as well as over and around it. A picket fence is an example of a permeable fence.
When wind hits either a solid or permeable fence, it puts a force on the fence known as wind load. Wind load affects the fence design.
- When wind hits a solid fence, it is diverted over and around the fence.
Determine the maximum wind speed in the area where you want the fence. The "Guide Specifications for Design of Metal Flagpoles" includes a map showing maximum wind speeds in the United States. This guide is issued by the American National Standards Institute and the National Association of Architectural Metal Manufacturers and is available online. Take a fence in a Midwestern area as an example. The maximum wind speed there is 90mph.
Decide on the type of permeable fence you want. The example fence is chain link.
Find an Internet site for calculating wind load on the type of permeable fence you selected. Many fence manufacturers have such sites. Some sites allow you to enter inputs and then display the output. Others provide documents describing how to do the calculation. Still others provide lookup tables. Use the Hoover Fence Company site in Reference 2 for the example.
- Decide on the type of permeable fence you want.
- Find an Internet site for calculating wind load on the type of permeable fence you selected.
Note any other inputs required by the site. Obtain these inputs. The example fence will be 3 feet tall and installed in a suburban area.
Different sites operate differently. Follow the instructions on the site to obtain the wind load. For the example, get the exposure category of B from Table 10. Then, using exposure category B, a 3-foot fence height, and a maximum wind speed of 90mph, get the wind load value q of 5.03 Kilogram per square inch from Table 14.
- Note any other inputs required by the site.
- Follow the instructions on the site to obtain the wind load.
- Design for maximum wind speeds in your area, not average wind speeds.
- Many manufacturers' sites go beyond wind load and provide the fence design parameters, such as post size and spacing.
- Putting up a fence is not a trivial task and sometimes requires special tools and skills. If you have never designed or installed a fence before, you would be wise to consult an experienced contractor. In complicated cases or where there are legal concerns, such as security fencing around a business, the design should be done by a professional engineer.
- In many locations, fencing must comply with local ordinances and/or homeowners' association rules. Obtain any required permits and permissions before starting to build a fence.
Cheryl Ess has worked in computer science for over 35 years. She has done technical writing for both government and industry, including work for the FBI and for well-known businesses such as Anheuser-Busch, General American and Monsanto. During her shorter career in engineering she wrote EPA operating permits. Ess holds Bachelor of Science degrees in computer science and civil engineering.