Many who don’t understand how wind works will state a product is rated to a specific wind velocity which is false advertising and not true.

“Rated to 180 MPH wind” is frequently seen in marketing materials which is a false and misleading statement that comes with many unwritten disclaimers.  

The formula that converts wind velocity to wind pressure has many variables. Each variable affects the resulting pressure for a given wind velocity.  A 100mph wind velocity for example can produce pressures as low as in the mid-teens (psf) to upwards of 50psf, even 60psf and more*.  These variables include such features as building height, location of the area on the building, terrain around the building, whether the building is on or near a hill, slope of the roof, size of the area in consideration, and more.

There’s even two types of wind speeds and pressures which complicates things further, Allowable stress design and Load Factored Design (click here for more) as well as different wind codes that govern (Some use ASCE 7-05, most use ASCE 7-10, and there’s now ASCE 7-16 with yet different conversion factors for some building surfaces for the same wind velocity).  Engineers deal with a common denominator when designing structures (wind pressure) which sets a uniform standard anywhere (yes even on the moon or mars) for a force which a product can resist.

Engineering Express® provides a free online tool to convert wind velocity to wind pressure.  Click Here to access it (using ASCE 7-10, others available under >Resources>Calculators in our web page menu).

 

* ASCE 7-10 Exposure D, 300 ft MRH, Zones 5 and 3 respectively, 10sqft tributary area, enclosed structure, flat terrain, Kd=0.85,  Forces upwards of 70psf + possible for hilly terrain, partially enclosed, Kd=1.0

Mar 8, 2018   457    Engineering Principles    
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