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Old 02-05-2013, 11:07 AM  
jjohnston
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Default Fence keeps blowing over

I built a fence a couple years ago. I used 4x4 posts which I planted 2-3 feet deep and cemented in. The fence panels I got are 6' high and 8' long. they were pre-built panels and it is a wood privacy fence. The fence uses 3 1x4 boards that the pickets attach to. I have 2 3" long screws in each 1x4 to hold it to the post. Every year in the winter we get a few times where winds get up to 50mph and it never fails, at least 1 or 2 panes get ripped out of the screws and land in the neighbors yard. the posts seem to be fine, its just the panels blow right off the posts.

Is there anything I can do to help keep this from happening? I thought about adding 1 washer on the top and bottom 1x4 to give it a bit more surface area to hold... but I don't really want to do that, because I think that would look a little bad...

Any help would be greatly appreciated!



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Old 02-05-2013, 11:24 AM  
mudmixer
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Washers will help as well as larger diameter and longer screws are the obvious things to do as you replace panels.

Once the panels are strong and attached, the next problem you may have is the posts and anchorage into the soil since they will see 100% of the wind.

Dick



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Old 02-05-2013, 12:19 PM  
Wuzzat?
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One or two panels out of how many? This info is more useful than if the whole fence fell or was not damaged at all by the wind.
http://en.wikipedia.org/wiki/Censoring_(statistics)

Use this to figure the force on the panels
http://www.ehow.com/how_6104140_calc...nd-speeds.html
but you may have trouble finding the pull-through force for hardwood/softwood boards for some screw head or washer diameters.
In that case, run an experiment using one or more people to simulate the wind force by standing on the loose & damaged panels, and try different size washers. Each doubling of the washer diameter increases the pull-through force by 4x. You may have to prime & paint fender washers for this.

You want the fasteners to hold 4x or more of the max expected tensile force due to wind. For your area there may be max predicted wind speeds that are not exceeded 90% or 95% of the time, see below.

Once this is fixed you may find out what is the next weak point in the fence structure.


SOURCES OF CLIMATIC DATA ON WUNDERGROUND
----------------------------------------

Hourly historical weather conditions are available for each day back through the beginning of records for most U.S. cities(as early as 1900) by using the drop-down menu under "History & Almanac". Set a date and hit "View".

"History & Almanac" is located on our local weather pages below the Current Conditions and Forecast sections under the title "Nearby".

We also provide a comma-delimited format. Click the link just below the tabular data to view the "CSV" format text.

You can also view our "Calendar View" "Yesterday's Official Weather and Almanac", and "Seasonal Weather Averages" there.

We also provide data from personal weather stations that can be found at the bottom of local forecasts pages. *Many of these station have historical data available.

OTHER SOURCES OF CLIMATIC DATA
------------------------------

The best source of climate data for the world is the National Climatic Data Center, located at:

http://www.ncdc.noaa.gov

The NCDC "CLIMVIS" option is a free way to get daily, monthly or yearly (but not hourly) data, see:

http://lwf.ncdc.noaa.gov/cgi-bin/res...imvisgsod.html

Click the button "I agree to terms", then click on the map presented to start choosing which data location you want to plot data for.

If you need more detailed data, you may have to pay money. Many of their products are free only to ".edu" domains, for more info check out:

http://www.nndc.noaa.gov/cgi-bin/nndc/buyOL-002.cgi

Other options:

1) There are 6 regional U.S. climate centers:
---------------------------------------------
Midwest: *******http://mcc.sws.uiuc.edu/ **********
West: **********http://www.wrcc.dri.edu/
High Plains: ***http://hpccsun.unl.edu/
Northeast: *****http://met-www.cit.cornell.edu/
South: *********http://www.srcc.lsu.edu/
Southeast: *****http://www.dnr.state.sc.us/climate/sercc/

2) Many local National Weather Service (NWS) offices keep some climate
data for their region on their web page. See
http://www.nws.noaa.gov/organization.html for a list of all the web sites
of local NWS offices.

3) Check if a public library in your area has the serial publication
"Climatological Data". This monthly is published for each state and lists
all official temperature, precipitation, snowfall, evaporation, soil
temperature, etc. daily observations from the many weather stations in
that state.

4) There is an excellent book called "The Weather Almanac" which
has climatological data for 100 cities across the U.S. You should be
able to find this at your local library.

5) A web alternative to "The Weather Almanac" can be found at:

http://www.cdc.noaa.gov/~cas/Climo/p...tates.txt.html

It has climate data for many US cities in a point and click interface. *It is a great alternative to a weather almanac for looking up average temp, precip and snowfall, plus, many states have very cool "relief" maps as the top level, so you get a sense of the topography of the state.

6) Canadian climate data:

Climate.Services@ec.gc.ca

http://www.cmc.ec.gc.ca/climate/

7) International climate data:

http://www.worldweather.org

This site has links to the weather services of over 60 countries. Some of these weather services have climate data for that country. Also,

http://www.worldclimate.com

has climatic temperature and precipitation data for most world cities.

8) Sunrise/Sunset, Moonrise/Moonset, Moon Phase, Moon illumination, Eclipses in the future or past:

http://aa.usno.navy.mil/AA/data/

9) Wind Rose data showing climatological values of wind speed and direction for 237 U.S. cities can be found at:

http://www.wcc.nrcs.usda.gov/climate/windrose.htm

10) *Historical pollen data is available at:
http://www.aaaai.org/nab/


http://www.wunderground.com/

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Old 02-05-2013, 06:33 PM  
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http://www.strongtie.com/products/connectors/fb.asp
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Old 02-05-2013, 08:50 PM  
Wuzzat?
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Fastener strength seems paramount here.

forces are in lbs.
50 >enter wind speed [WS] in MPH
PSF = 0.00256xWS^2
6.4 =calc'd PSF
48 >enter sq. ft.
307 =calc'd force
2 >enter 2 for flat, 1.2 for rounded
614 =calc'd total force
4 >enter # of fasteners
154 =calc'd force on each fastener
4 >enter safety factor
614 =calc'd ultimate strength for each fastener

For 75 MPH wind you need 1380 lbs/fastener. No wonder your fence is failing.

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Old 02-10-2013, 12:13 PM  
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I'd be strongly tempted to modify the panels, creating some gaps to let the wind through, instead of installing hundreds of washers. Pulling every 4th vertical plank would take a lot of pressure off each panel. If privacy is a concern, re-mount the removed planks (with spacers, if necessary) on the opposite side of the fence rails.

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Old 02-10-2013, 02:11 PM  
Wuzzat?
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Quote:
Originally Posted by BridgeMan View Post
I'd be strongly tempted to modify the panels, creating some gaps to let the wind through, instead of installing hundreds of washers. Pulling every 4th vertical plank would take a lot of pressure off each panel. If privacy is a concern, re-mount the removed planks (with spacers, if necessary) on the opposite side of the fence rails.
Yes.

Our fence has overlapping vertical boards which must present less resistance to wind than would solid panels and still gives privacy.
http://www.google.com/search?client=safari&rls=en&q=fence+types&oe=UTF-8&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=Yf8XUYPYGMeR0QHn8YCIDg&biw=1020&bih=764&sei=Y_8XUfDjNKbg0QG_zYFY#imgrc=SN6tajH38MYlhM%3A%3BvARCXkirkE4nvM%3Bhttp%253A%252F%252Fwww.1888fencing.com%252Frte_images%252FiStock_000003992963Small.jpg%3Bhttp%253A%252F%252Fwww.1888fencing.com%252Ffence_types.html%3B847%3B567
Another way would be to have some vertical boards weakly fastened or hinged at the top, others more strongly fastened and some percentage really bolted in place.

I saw an ad by a fence post maker showing data on what wind force their posts and other types of posts could resist.
Problem was, they were galvanized steel and not so pretty.


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