Pole building failure mode structure design

[fastline12]

I have been scratching my head for some time here as I work on a design for a couple buildings I need. I will be building wood pole buildings and all poles, or rather multi-plied 2x materials, buried in the ground approx 4ft and concreted in place. After some research, I will find a solution to isolate the wood poles from soil contact to increase building life since that seems to be a common failure mode in them.

however, living in Tornado alley, I have to plan for complete structural failure in which breaking the beams at the ground is what would likely happen. The issue is that once they are broke, there is no way to replace them such as a steel I-beam building. The concrete piers are poured around the poles, then the floor is poured over that so everything is locked up solid. Even if I decide to raise the pier pour to concrete pad height, that means jack hammering out a LOT of poles.


I would love to come up with a solution that would allow me an easier repair should the need arise. Does anyone have an idea here? The only other thought I had was to run a huge auger through the 4ft of buried lumber to extract it, repour that as concrete, and use that as my support pier for I-beam construction BUT the issue is dimensionally, the building will be made for wood structure and I am sure trying to make that work with I-beam will not work out. Much easier to go back with wood.

The reason for selecting wood unfortunately has to do with my county appraiser and taxes. The steel building will cost me TWICE as much in taxes and continue to go up, while the pole will decline.

 

[Tmoose]

Probably need some upgrades to allow for uplift, and use more capable moment connections up above, but I was thinking of something like this -

http://www.ozcobuildingproducts.com/uploads/PRODUCTCATALOGFINAL.pdf

http://www.tapconet.com/vloc-division

http://gordonmetalproducts.com/postcaps.php

 

[IRstuff]

Why the 4-ft? Is there a structural reason for this?

You could possibly do something similar to Tmoose's second link, where, instead of the v-lock post, you have a 4-ft deep metal receptacle. Then you have a plate and collar for the post that you can fasten to the post 4-ft from the end. Drop the post in so that the collar is nestled in the receptacle, and bolt down the plate to the receptacl flange.

TTFN
faq731-376

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[fastline12]

I appreciate the reply. I am not sure any of those solutions would work for this but I think you are offering ideas? And I think you are giving me one. Possibly if we we design in drive blocks in with the pour or some mechanical feature where we could pull them out with an excavator or what not that would release the poles? Like a wedge clamp?

One of the concerns I have just in general is the pole barn was originally intended as poles in direct contact with the soil. Wood changes dimensionally moisture and time. Our county of course does not care about this and required the poles be concreted in place. This means that if the lumber shrinks, which it would because it would be arsenic treated lumber, the concrete would lose tension on the lumber.

As well, the concrete is intended to offer uplift protection for the structure BUT if you do this right with a concrete floor, that whole floor can offer uplift protect and that along with poles properly set in the ground, I really doubt concrete is needed. In either case though, shear lugs on the sides of the poles would help tremendously in uplift protection.


I had the idea to use flowable fill for the pole backfill but I don;t think that stuff will move once set but maybe the earth pressure around it would force it down on the lumber? Just a thought but it sure seems like concreted poles is not going to be very advantageous. However, in any case, measures need to be taken to keep the pole dry to prolong life.

 

[drawoh]

fastline12,

This question would be better asked in forum507. The experts there may have some nasty surprises for you.

--
JHG

 

[fastline12]

IR, the 4ft depth is a county minimum but we will have to stamp the plans anyway because we are exceeding their standard height. Actually, even at 4ft, the uplift numbers don't look real good. Should be fine with a floor in it but I will want some extra protection in the ground. We also plan to over design the pole's sizing to hopefully force failure of the sheeting first which would get the load off the poles but we cannot predict flying debris damage. Big Oak tree strike is going to level anything it hits. We hope that day never comes but I want procedures in place for fast repair.

 

[fegenbush]

drawoh is correct in directing you to structural engineering. Some questions to consider:

-What type of reinforcement will you use in the concrete slab floor?
-The connection detail between a concrete footer and a post is a basic feature. Have you researched the common connection details?
-Have you looked at the frost depth to see if that is why the 48" minimum exists?
-What species of wood are you using to design the columns and other members?

I am not attempting to be contrary, but there are many things to consider when designing a structure.

 

[SnTMan]

fastline12, set some 4 in sq X 1/4 or 3/16 wall steel tubing in the concrete. Make them extend above grade enough to get the moment resistance you need. Set your 4 X 4's in them. Put enough fasteners thru the tube into the wood to get the uplift resistance you need. When your tornado wipes the slab, fish the broken ends out of the tube and re-build.

Steel might eventually rust away but, you're not building for the ages, right

(PS I live in TC, too. Never been hit yet, he said...)

Regards,

Mike

 

[dvd]

Insure the building against tornado/wind damage and forget about it. There are a lot of buildings in tornado alley that have never been damaged. Seems like you may end up with damaged footings no matter what you do. Keep your costs low and spend the money on insurance. Also, is a fire more likely than a tornado?

 

[boo1]

Might be cheaper to increase size of your poles