slab in pole barn. what to do with poles?

[Woodsman_Pete]

Don't set the posts in concrete, I've pulled posts in both instances, the posts that were set in dirt and compacted with a digging bar looked like new after 15 years, the posts that were set in concrete were almost rotted in half, both posts were treated 6x6 posts 16' tall in a pole barn used to store round bales. As far as pouring your slab against them I would nail an expansion joint material right to the post, you can buy it at any Home Depot or Lowes or simalar, it is 4" high and 1/2" wide and comes in 10' lengths, a tar soaked fiber membrane which can be cut to length with a utiliy knife and nailed to the bottom band board and around all 3 sides of the posts with 1 1/4" roofing nails. An added advantage of using this expansion material is that you set it to grade at the top of the slab and it creates a ledge for the screed board ride on.

 

[Darren]

I agree with Pete. For what it's worth CCA treated poles rated for constant salt water immersion are still available. I suspect you could pour concrete around them and they wouldn't rot.

 

[kevinO]

Thanks a lot for all of the pointers. I'm still planning. And saving. The materials costs is going up at about the same rate that I'm putting $$$ aside! /forums/images/graemlins/frown.gif

Here's another, related question: I saw wroughtn_harv's barn and saw that he used steel pipes instead of poles. Looks like a neat idea.

So I assume that there is no problem putting steel pipes in concrete?

Assuming that this is OK, then my next question is regarding the size and thickness of the poles. I've read many times that if you're using wood, go with 6x6 for corners and 4x6 for non-corner supports, eight foot on center.

What would be a reasonable steel replacement for the poles, eight foot on center? I'm thinking that for my needs, square tubing would be easier to work with instead of round. What size? My garage has steel supports for the garage door that are 3x3x3/16". Would that be big/heavy enough to replace a 6x6 wooden post in a pole barn?

I have lots of questions and few answers!

Kevin

 

[phantom309]

Hi Kevin-

</font><font color="blue" class="small">( What would be a reasonable steel replacement for the poles, eight foot on center? )</font>

I'm no expert, but I've been studying questions similar to yours for a while and have a little to offer. Disclaimer - I'm not a structural engineer. I am an electrical engineer, but that really doesn't help much here! /forums/images/graemlins/smile.gif

A while back, I bought this book on building trusses, etc out of wood and steel members. In that book (and one other at home), I found a table listing the maximum load for wood members in compression. For an unbraced length of 12 feet, it lists a max load of 6,200lbs for a 4x6 and 17,400 lbs for a 6x6.

Flipping a few pages to information on members made of structural steel tubing, and running some figures involving, L, A, r, I and other letters of the alphabet ( /forums/images/graemlins/smile.gif ) reveals a maximum compression load of 18,700 lbs for an unbraced (12 ft long) 3x3x3/16. Stepping up to a 1/4" thick 3x3 and you get 22,900lbs.

A 3.5x3.5x3/16 jumps to 29,000.

So certainly something as "small" as 3x3x3/16 looks adequate in this area. There is also a consideration of both bending and compression forces applied at the same time which would be the case for a post in a building that is subject to live and dead loads and also wind forces.

The calculations here are a little more lengthy so I took the short route and ran the numbers in some finite element analysis software that I have that is for just this purpose.

Applying a dead load of 6,000lb at the top of a 12 foot member with a 300lb/ft wind force being applied along its length resulted in a displacement in the X direction (top of post bent to side) as below:

3.5x3.5x3/16 steel tube: displacement: 12.7in
5 1/4 x 6 glulam wood post: 13.5in
6x6 post: 14.9in
4x6 post: 23.2in

So these numbers also suggest that something along the lines of a 3 1/2 x 3 1/2 post should handle both compression and bending forces better than a 6x6 post or a 5.5x6 Glulam.

For those that have talked about glulam posts in the past, this test suggest that they can indeed outperform (slightly) larger "normal" posts!

Can steel posts be planted in concrete without worry about rust? I don't know?!? If you're as **** as I am, you might slap some oil base paint on them before you stick 'em in the crete if you'll lie in bed worrying about such things! /forums/images/graemlins/wink.gif

I guess that one question that I have is, if steel would work as a replacement for wooden posts, (and it looks to me like it should), why doesn't anybody use it???

Maybe somebody else can weigh in on this...

Best,


Mark

 

[kevinO]

Thanks for the update. I'm still thinking on what way to go RE the poles.

Here's another question for folks with some (any is more than I have) experience with building pole barns:

How do you attach the (I think they're called) "eave girts" to the poles? The "eave girts" are the 2x12's (or something close) that the roof trusses sit on at each wall. If you are using a 6x6 post and have two eave girts that butt at that pole, you only have 2.5 inches or so of overlap between the girt and the pole - that's not much area to put nails, bolts, screws, etc. Given that the eave girts carry all of the weight of the roof, this connection needs to be strong.

Are there any tricks/hints to make this connection strong? Any connectors to help with this?

Thanks in advance.

Kevin

 

[Kevin_in_VA]

Whenever I set posts I usually give them a few heavy coats of oil based paint to about 8 to 10 inches above where the final ground level will be before putting them in the hole and pouring around them. That way they are protected from moisture. I typically pick up some OOPS paint at my local Lowes or Home Depot for this purpose.

Kevin

 

[Kevin_in_VA]

</font><font color="blue" class="small">( How do you attach the (I think they're called) "eave girts" to the poles? )</font>

I would notch the poles to accommodate the width and height of the beams and bolt them to the posts. Roof loads are usually vertically compressive, but there is some sideways loading as well. This way the bulk of the support will be in the vertical direction, but still provide some lateral support.

Kevin

 

[bczoom]

OK, I'll throw out my 2 cents.

KevinO
Welcome to TBN.
Please fill out your profile. Your location "may" have some impact. (e.g. freezing and stuff).
Can you give us a little more info on this project? How big is the building going to be? Are you going to run any posts up the middle or leave it wide open?

Now, again, this is just my 2 cents but I've built several things similar.
These references are based on one of my pole buildings (32'x48', 10' ceilings)

For the posts. I went 6x6's on the corners, 4x6's 8' on-center inbetween.
To set the posts, I went all the way to ground level with concrete, directly on the posts. Although I didn't coat with anything, take the advise of others here and paint or something.

For the concrete slab:
First, do any plumbing... needed below the floor. Floor drains and the like.
Lay about 4" of gravel over everything, including the concrete holding the posts.
(optional, but I did it) - put down plastic sheeting as a vapor barrier.
Put expansion joint (the stuff Woodsman_Pete mentioned) around everything that the concrete will come in contact to vertically. Posts, sill plates...
Pour your concrete. Also consider a threshold around the perimeter that's at least 1' wider than your overhangs. Slope these thresholds about 1" to keep water away. Gutters on top, drain tile at the end of the thresholds will help get the water away.

For what you called "eave girts" (I call headers), using 16 penny nails, nail directly to the side of the posts. On a 2x12, about 8 nails should do it. The shear strength on a nail is awfully high.

What are you going to use for siding?

OK, after writing all that, I thought I'd take a couple pictures of one of mine to give you an idea. Here's the first pic just to give you an idea of the building.

 

[bczoom]

This picture is a little closer.
Around the perimeter, the concrete extends past the roof and gutters and is sloped away from the building. Underground is 4" drain tile just off the end of the concrete to catch whatever the gutters don't.

 

[bczoom]

Here's a view of the top of the post with the 2x12's