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RE: Wind Load on Wood Fence

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Jeff & Ralph,


Interestingly, I recently calculated the wind load on an 8’ freestanding masonry fence, 90mph Exposure B, using ASCE 7-05 Section 6.5.14. The point force I got for the worst-case scenario at the end zone (first 8 feet) of a very long (100 foot+) fence translated to a uniform pressure of 25.5 psf.


For the record, I assumed G=0.85, Kd=0.85, and I=0.87.


Took me 2 or 3 days to generate a matrix duplicating Figure 6-20 Case C. Although a good portion of that was fiddling with Excel and figuring out how to create little drop-down menus I could use to change occupancy category, exposure, and other things.



Gary J. Ehrlich, PE
Program Manager, Structural Codes & Standards
National Association of Home Builders (NAHB)
1201 15th Street, NW, Washington, DC 20005
ph: 202-266-8545  or 800-368-5242 x8545
fax: 202-266-8369

Attend the 2009 International Builders' Show
January 20-23, 2009, Las Vegas, NV


From: Jeff Smith [mailto:jeffsmith7(--nospam--at)]
Sent: Wednesday, December 17, 2008 9:17 PM
To: seaint(--nospam--at)
Subject: RE: Wind Load on Wood Fence


Ha! You don't want to calculate the fundemental frequency of a wood fence post and the gust effect factor?

25 psf for a fence in downtown SF seams pretty high.




From: Rhkratzse(--nospam--at) [mailto:Rhkratzse(--nospam--at)]
Sent: Wednesday, December 17, 2008 6:09 PM
To: jeffsmith7(--nospam--at); seaint(--nospam--at)
Subject: Re: Wind Load on Wood Fence

I'm with you Jeff.  I have a similar little project right now and a glance at 6.5.14 and its interminable references to references, etc., make me think it'll take as week and 50 pages and a Ph.D. just to get the pressure that used to be simply 25 psf.


In a message dated 12/17/08 6:04:37 PM, jeffsmith7(--nospam--at) writes:

I was hoping there might be a simplified procedure. The the 97 UBC allowed 75% of the normal force method for fences less than 12'.

From: Conrad Harrison [mailto:sch.tectonic(--nospam--at)]
Sent: Wednesday, December 17, 2008 5:53 PM
To: seaint(--nospam--at)
Subject: RE: Wind Load on Wood Fence

Seems the right approach to me. We use pressures on free standing walls for fences. If open then use the drag force coefficients for open framing ( AS1170.2). When using ASCE7-05 looks like need to go elsewhere for open framing drag forces.
Conrad Harrison
B.Tech (mfg & mech), MIIE, gradTIEAust

South Australia

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