Considerations for sealing wood beams for ground contact

[fastline12]

I am trying to come with a solution to seal engineered poles or beams for long term ground contact. Actually will be concreted in place but the general understanding with wood rot is the combination of O2 and water is what causes rot. Either is missing and rot does not occur?

I have seen everything from tar, to plastic bags, to injections to protect the wood. I am considering a bit more invasive operation of fiberglassing the outside of the beams. I know fiberglass would have the durability and longevity for this application but I do have concern of locking in any moisture and thoughts of any dimensional changes of the lumber causing issues?

I have also thought of some type of molten plastic dip as well. I just don't think people take this issue seriously enough as it seems to be the prime issue regarding these types of structures.

 

[Tmoose]

"Natural contraction of the lumber could cause them to be loose."

Any embedded posts or 2X lumber I've been around have been TIGHT. A few times folks greased up some slightly tapered 2X for removeable formwork and they could not even be chiseled out. Maybe after 15 or 20 years its a different story.

 

[chicopee]

My father in law used a copious amount of used motor oil on the sill plate of his garage. This garage is over 60 years of age and to date there were no signs of infestation eventhough abutting the garage was a vegetable garden.

 

[btrueblood]

Google Timbersil. Sodium silicate impregnation under pressure for a fairly long time period (days I think), followed by a heat treatment; it was studied/developed at U of Wash. IIRC. Stuff is guaranteed for 40 years, longer than some (most?) plastic/composite decking.

 

[fastline12]

Some type of concrete in the ground sure makes more sense so I would never have to worry about lumber in the ground. BUT, this just adds a LOT more complexity in the design and then I need to design and fab specialty splice plates to join to wood above ground. Still just not sure if it is worth all that.

However, I still have to design for tornado failures and rebuilding. The first thought that came to my mind in a pole system is, "when the poles snap off flush with the slab, how do you fix that?" My design originally was to sister additional lumber on each side of the poles up a few ft from the ground to promote failure above ground.

 

[RBPrice]

Do not put the posts into the ground but support them on concrete pillars poured into one of the proprietary cardboard tubes like "Sonotube" obtainable from Lowes or Home Depot. Put a 15 inch length of rebar in the top of each post with 8 inches into the post, trowel a slight radius to help shed water, use pressure treated lumber and the barn will last several hundred years. Lay out the location with a transit and string and hire a back hoe with a rotary drill attachment to drill the holes.

Note that your local building code will probably require that either the bare posts or the concrete columns will have to go down four feet to keep them from frost heaving. Mine are only six years old but I suspect my great grand children will have to auction the barn off.

Bob Price





Bob Price
A*G*M

 

[fastline12]

Thanks Bob. How do you accommodate the bending loads on the vertical column with only a piece of rebar stuck in the bottom of the wood? I was thinking up something nearly exactly the same as what you propose but with a much more radical connection and a small concrete "post" formed up to get into the dry building space before connecting to wood.

A member above shared a link to concrete posts which gave me some ideas. However, I think the concrete blend will have to be polymerized, possibly add glass, and a good rebar structure just to ensure that area could never fail before the wood poles.

I am also considering that this is getting into a rather complete build design....Pole barns are supposed to be SIMPLE! lol

 

[ornerynorsk]

A wood beam to a concrete pad would still need to be a bolted connection, not simply a piece of re-bar inserted into it. If the project is an engineered beam (glulam or microlam?) are the viability periods for those out past 100 years?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[RBPrice]

Lateral loads on the posts would be taken with beams bolted to the posts just above the concrete similar to a sill plate in a framed house except they are on edge instead of flat. Bending loads induced by wind loads across the barn would be taken by the roof trusses with triangular beams from the trusses to the posts. Lots of triangles are good things in a barn design. We live in upstate NY at an elevation of 1140 ft. MSL and it is frequently very windy: 55 + MPH. Our barn is 25' x 40' with the 25 ft. end facing the westerly winds. So far we have had no problems with the structure including a minor earthquake.

Bob Price
A*G*M

 

[Tmoose]

Code in Virginia 1807.3

http://www.ecodes.biz/ecodes_suppor...ion/PDFs/Chapter 18_Soils and Foundations.pdf

Colorado "guide"

http://www.coloradochaptericc.org/pole-barn2k09.pdf

concrete embedded pressure treated poles seem to be the "standard" , at least if I'm trying to avoid needing an engineers approval

 

[dgallup]

Do not put the posts into the ground but support them on concrete pillars poured into one of the proprietary cardboard tubes like "Sonotube" obtainable from Lowes or Home Depot. Put a 15 inch length of rebar in the top of each post with 8 inches into the post, trowel a slight radius to help shed water, use pressure treated lumber and the barn will last several hundred years. Lay out the location with a transit and string and hire a back hoe with a rotary drill attachment to drill the holes.

Note that your local building code will probably require that either the bare posts or the concrete columns will have to go down four feet to keep them from frost heaving. Mine are only six years old but I suspect my great grand children will have to auction the barn off.

Bob Price

That is how (with the exception of the sonotubes) the overhang on my Mother's barn was supported. The house is 200 years old but the barn is newer, probably only ~100 years old. We had to replace one of the corner support posts last year because the gutter downspout had rusted out and was letting the water run down the post. If that had been maintained properly the post would still be as good as the others. Had to jack up that corner of the barn and replace the 12" square by 8' long post. We used solid oak. This post won't take any bending loads.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[mikekilroy]

Our 1850 pegged oak beam barn rebuild recently used those 36" deep 12" dia sonitube cement supports with short rebar into the 8" sq oak 12' verticals for the extended overhang wall support. But the huge weight of this solid oak beam full size barn w/ 1" thick batten board siding I think allows this above ground cement to wood joint on one side - more like a porch overhang....

But our 40x60'x20'h pole barn with metal siding weighs NOTHING. Such a joint in OH winds would simply blow it away! It is like a sailing ship. There is no way I would ever even contemplate anything less than solid cca treated 8x8 BURIED below frost line timber for the vertical supports. If you any less you will not have to worry about it standing 100yrs!

http://www.KilroyWasHere<dot>com

 

[MintJulep]

and then I need to design and fab specialty splice plates to join to wood above ground. Still just not sure if it is worth all tha

Or just use one of the many commercially available connectors that are made exactly for this situation. This one for example:

http://www.strongtie.com/products/connectors/cbsq.asp