post setting technique

[Zone_V]

I wanted to get some of the group's opinions on setting treated posts for a pole building/garage. Obviously I want the proper depth, hole diameter, etc., but I've heard two opinions on "backfilling" the holes. It seems to be the consensus that one should have a concrete pad in the bottom of the holes, but I've heard it argued that the holes should not be filled with concrete around the posts since the pH or whatever is damaging to the wooden posts. On the other hand, I've been told that concrete is preferred to just soil to backfill for the advantage of strength and wind resistance......
Any engineers out there or anyone with experience in this issue? Thanks in advance for your ideas. John

 

[PaulinSD]

The drawings for my new 30' x 48' building shows 18" dia. precast concrete footing. They will drill through the poles (4x6") and insert 3 #4 x 12" rebar, add 4- 60# bags sack crete to prevent uplift. The rebar is about 4-6" above the top of the footing. The salesman indicated that in wind prone areas, they will fill the holes to the top with concrete for added weight, hence prevent further uplift. Poles are treated, no worry about concrete/water. Hope this helps.

Paul

 

[radman]

I built a pole barn this summer with treated laminated posts made from 3 2x6's tied together. Cleary, Astro, Morton and others use this method. The laminated columns sit on precast cement pads ("cookies"). On my building, additional pressure treated 2x6's are nailed on all 4 sides of the columns at the bottom with galvanized 4" 4d nails. 5 nails per block and each block was 12" long. It is these nailed blocks that resist the poles from being pulled out of the ground by wind lift. The posts were other wise tamped in the ground.
Each column is 4' in the ground and sit on 14" cookies and the columns are 8' apart. The building is 45' x 72' x 12' high. Building is engineer rated for minimun 80mph wind load and 30" snow load (required by code).
I am not aware of any commercially available building that has cement poured around the columns entirely. I have heard of some placing a pin (bolt) through the bottom of the column and partially cementing the bottom around the pin to hold the column down during strong winds. If you have ever tried to pull out a crooked post or a post with a wider bottom than the top, it takes a lot more lifting force than a post with uniform smooth, straight sides.
A freind told me he once heard of a pole barn shed lift 2 feet out of the ground during a very strong wind and then settle back down in the hole. He said a chair blew under the edge of the building and was crushed when the shed came back down. This is how they knew it lifted at least 2 feet.

 

[JerryG]

Zone,
I have a 20’ x 120’ pole building that we built in 1972. We dug the holes, set the poles and back filled with dirt. If anything it is more solid now than when we built it.

 

[WVBill]

If you live where you will need permits and inspections then obviously you'll need to comply with code. If you are building your pole barn from a set of plans then go by the pole setting detail in the plans.

If, like me, you are design/building it yourself, I found a great deal of information in several books on pole building construction that I got from <A target="_blank" HREF=http://www.amazon.com/>amazon.com</A>. Go there and search for "pole building". Any or all of those books will give you valuable information.

Now, what I did was set my 6 x 6 PT poles into 4' deep holes and backfill with concrete. My father-in-law is a retired Navy Sea Bee Master Chief and I followed his on-site advice. The barn has been up for two years and seen some pretty firece winds with no sign of lifting, twisting or shifting.

 

[beenthere]

From the standpoint of decay (not stability) of the post: Setting treated posts in concrete is not a good idea if there is a chance for water to get between the wood and the concrete. However, if protected from the effects of being enclosed with building material, then there is not likely a water problem, hence a problem of decay. However, for a post in the open (fence, utility, etc), then look for decay in about 5-10 years if cast in concrete. It happened after 7 years to a local ball diamond set of big utility light poles - they were completely rotted through except for a 1/2" shell on the outside. The depth of penetration of treatment in wood is one of the factors, as well as wood decays in presence of water, unless completely submerged. Best to tamp the exposed posts with dirt or small gravel (good strength too) and the recommended attachments to the post to resist lift. Check with a wood source such as Southern Pine Inspection Bureau.

 

[cowboydoc]

I have probably built or helped build over a couple dozen barns over the years and everyone we have built exactly as Radman explained. We didn't used to have the engineered posts but I have used them on the last five barns that I've built. We have barns back home that we built when I was a kid this way that have never moved even one inch. I've built six out here and not a one of them has ever moved as well. One thing that hasn't been mentioned is that I would go a minimum of 4' with your posts. If you use the concrete pads to set your posts on they are usually 4-6" thick. Make sure you go 4' to the top of the concrete pad and not the bottom of the concrete pad.

 

[StoneHeartFarm]

Zone_V

Required depth here is 42" by Code, so I agree with everybody else, go 4'. I just had my barn put up, and basically, the contractor dug holes, tamped the soil, slid in the poles and backfilled with concrete. Don't know if he attached anything to the poles first or not. I've seen barns rolled over by high wind, but not many, so I think it comes down to pole depth and whether the barn had a slab.

I don't know about your area, but if you are planning to use anything but a standard 8x7 or so door (or 8x16), you might want to search around for availability. I've been waiting on my 9x10's since November. Lumber Yard had them in between Christmas and New Years but damaged them when loading and now I'm stuck waiting.

Another advantage to the laminated beams would be that they are relatively straight. Around here, most barns are built with treated 4x6 and they are not straight like 6x6's. I'm told that this is normal for all lumber. That 2x6's are as a rule straighter than 2x4's, etc.

SHF

 

[Zone_V]

Gents
Thanks to all who took the time to pass along their thoughts. I will certainly be able to apply the ideas to my project.
John S. aka Zone V

 

[Mike H]

Here's a couple of #'s that can be used as a relative reference (this comes from the Midwest Plan Service based on some AE testing at Oklahoma State and U of Illinois):

Load required to withdraw a 5.5" pole 1"

Pole w/ earth tamped around it = 1600 lb
Pole w/ a collar of concrete at surface = 1200 lb
Pole w/concrete at base extending up pole ~ 6" = 5500 lb
Pole on a concrete pad then concrete added ~ 6" = 3500 lb
Pole w/ concrete at base extending up pole ~ 6" installed as dry mix = 4500#

The recommendation of this reference is "nail treated lumber to both sides of the post; run a rod through the post and encase the butt in a concrete footing; or dowel the post to a concrete floor"