How to Stop Fence from Leaning ?

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Hi,
I have a privacy fence at ground level, that gets a lot of wind. It has started to lean. I have placed a heavy piece of outdoor furniture next to it, but it gets moved over eventually, and leans again. I have also wedged pieces of wood into the ground next to the bottom, and it helps for a while, then the leaning starts again.
Thanks
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You might supply details of the fence dimensions and how the posts are currently anchored if anyone is to provide meaningful advice. Joe G
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On Wed, 17 Mar 2010 10:04:46 -0700 (PDT), utilitarian

    How tall is the fence, how deep is the foundation, what materieals were used, how old is it, what condition, what kind of soil condtions?
    How are the neighbors fences doing?
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Fence is 6 feet tall. About 11 feet long. Three posts ( 3.5 in by 3.5 in) going down into ground, don't know how deep. Doubt there is any concrete. 20 years old. Don't know what kind of wood it is. The wood above ground is in good condition. No rot. Soil is often damp, clay. Mostly in shade. No comparable neighbors' fences around to compare.
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utilitarian wrote:

By the age and conditions, they're probably about rotted off below ground.
Wet clay ground will move when force applied as well unless there's sufficient depth to be to really solid dirt to resist.
The wind load of a solid fence is pretty good when look at the cross-sectional are times the velocity-squared term to convert from speed to pressure and the area multiplier to force so takes a pretty good counterforce on just the area of the posts to counteract that. You're taking 66 sq-ft and counter-balancing that w/ <4"/12"-ft*(say)3-ft (probably optimistic) depth --> 66:1 ratio w/o the moment arm difference of 6ft/2 vs 3-ft/2 as midpoints of another factor of 2 besides. That's all quite approximate to an actual force/moment diagram but gives the overall picture of what's going on.
That 132:1 ratio/#-posts is the actual multiplier so if it's got the two ends and a center for a 5'-6" spacing, it's "only" 44X the wind load at each post.
The fix probably means replacing the posts if I had to guess because they're gone or near so and either add depth or backfill w/ concrete or other means to be more stout. It's possible, of course, that it was good enough originally and it is just the posts rotted w/ time.
--


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You can listen to all these numbers / ratio BS like this guy dbp (aka pointdexter) is spewing or you can listen to me - dig up and set new posts in cement. Bury posts 1/3 the height of the fence. My privacy fence withstands winds of 60-70mph. Does not move / will not move. Regards
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wrote:

Curious. How deep is the frost line, experiencing any frost heave? Some posts may need to sink 4 feet.
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jim wrote: ...

You be wrong there, good buddy, whatever you think... :(

Well, if you would read what I wrote, in essence I'm agreeing w/ ya' that in all likelihood his posts are gone...and needs new. The "ratio BS" as you call it simply serves to demonstrate to OP what he's expecting a small cross-sectional area to do.
The concrete will, in fact, increase the cross sectional area and hence the resistance force by that factor. The down side to setting a post in concrete in a wet area is that it traps water around the post and thereby may promote the rate of decay.
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Also, in heavy frost areas, the concrete 'plug' surrounding the post can be 'heaved' by frost action. Here (cold climate next to the North Atlantic), the recommendation is that concrete be applied to the base of the post, well below ground level, but not all the way up to ground level. Thus avoiding something that frost can exert an upwards pressure on.
BTW: One formula I 'seem' to remember for wind pressure was;
Force in pounds = 0.003 x wind speed (in mph.) squared Hence a fence 11 feet by 6 feet; i.e. 66 sq.feet. in direct wind against one side .................... At 1 mph = 0.003 x 66 = 0.2 lbs At 2 mph = 0.012 x 66 = 0.8 lbs At 10 mph = 0.3 x 66 = 20 lbs At 20 mph = 1.2 x 66 = 80 lbs At 40 mph = 4.8 x 66 = 320 lbs At 80 mph = 19 x 66 = 1270 lbs At100 mph = 30 x 66 = 1980 lbs
Noticing that as wind speed doubles the force just about quadruples!
So any fence whose posts are already deflecting at all won't stand much chance in a 'good blow'.
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terry wrote: ...

That's expression for pressure in psf, not force.
About 0.00255 v^2 iirc from design days (many moons ago)... :)
...

Well, if "just about" includes "exactly"... <VGB>
Since F ~ PA and P ~ V^2, that's pretty much what it has to do... :)
...
--
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In english please?
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jim wrote: ...

????
Seems pretty straightforward prose to me...
--
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jim wrote:

(snip) or you can listen to me - dig up and set new

Nobody else said it, so I will - never set wood in a completely enclosed concrete pocket. Dig the hole extra deep, and put gravel in the bottom. Put in the post, and about 6-8 inches of tamped gravel up the sides. THEN pour your concrete in the hole. As others have noted, frost can make the ground spit out the concrete, so if you can make the hole a bit of an upside down cone, it will better resist heaving. (not hard with a decent post hole digger, unless soil is sandy. (for deck and basement pole footers, a lot of people like the leave-in-place plastic forms shaped that way, but that is way overkill for a fence.)
As to if you should bring the concrete all the way up to daylight- if you do so, make sure to shape the top so it doesn't puddle water against the wood. IMHO, stopping it it 3-4 inches below grade makes it easier, and reduces how much water will run down the post into the concrete.
--
aem sends...

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On Thu, 18 Mar 2010 09:45:11 -0700 (PDT), utilitarian

Take a post hole digger and dig down next to the posts. See if they are rotted. If not, dig all the way around and fill with concrete. If they are rotted, replace the posts and use concrete. You can likely salvage the rest of the fence if it's still good. Just saw the nails off the post with a sawsall. The posts may be too short too. You wont know till you dig. They should be at least 30 inches in the ground. If its a 6 foot fence, I bet the posts are 8 footers / 2 feet in the ground.
If you just want a cheap and quick fix, drive some metal posts (T-posts or pipe) into the ground next to the posts, and put lag bolts thru the metal into the wood posts. Of course be sure the fence is straight and level when you use concrete or steel posts, ot it will be leaning forever.
Mr. Fixit
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snipped-for-privacy@theshop.com wrote in wrote:

I saw a fix on one of the TV home shows where they used a metal post reinforcement that got hammered in right against the post,then screwed into the post. It seems that the post can rot under the surface and not be seen,but the post breaks below ground,and you get lean. They also did a post replacement,and used rock and gravel to provide drainage around and under the post so the rot would not reoccur with the new post.
--
Jim Yanik
jyanik
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Dicking around trying to shore up the fence and fretting about it, you've wasted more time than it would have taken to completely rip the fence out and reinstall it properly. Three posts, two panels... You could have it done in an afternoon even if you hand-dig the holes by yourself. Less if you have help.
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snipped-for-privacy@hotmail.com wrote in wrote:

My fence was put up in 1978. Stockade fence 6 feet tall. The first year it started falling/leaning. My husband called the company back and had them install galvantized posts. Problem solved and the fence still stands straight.
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utilitarian wrote:

Diminish the force of the wind (by cutting holes in the fence) or strengthen the fence (deeper foundation) or external means (guy wires or diagonal supports).
The remaining option, blowing back, is not practical.
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You have to either dig deeper and use longer posts, put the post in concrete, or add more posts.
You can add heft bracing behind the fence but that causes other problems as they are in the way of grass cutting, tripping hazard, etc.
Since the fence is already leaning, the supports are loose in the ground and you have to dig down to fix them properly, possibly set them in concrete.
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utilitarian wrote:

Hi, If it is fairly new fence, not installed correctly. Can't do a patch work. Problem will repet. Start over from scratch?
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