Looking for some Pole Barn framing suggestions

[mx842]

Thanks for all the great input. Right now I'm leaning towards the "bigfoot" footers, from what I've read, if I scrape down everything soft and get a layer of concrete on the hard layer underneath it right away (<24 hours), it should seal pretty well. I'm thinking scrape off the soft shale with the backhoe, place the footer with rebar mounted vertically and pour 12 inches of concrete into it. Let it set and then drop the post in place and pour concrete around it to fill the footer and sonotube above it. Planning to backfill with gravel as much as possible to provide extra support around the footer.

I put my barn on 12" round piers and attached them with angle straps that I made in my shop. I made them out of 2X2, 1/4" angle iron that I cut in 5 1/2" lengths. Then I got some flat bar that was 4 to 5" wide and I cut those into 6" pieces. I laid the angle pieces on my welding table and welded a piece of flat bar to each of the angle pieces until I had enough of them. When I was done the part ended up being an angle bracket that was 2" X 7 1/2". I drilled a 1/2" hole in the center of the 2" part and two 3/8" holes in the upright part several inches apart.

I then mounted the brackets to the piers using 1/2" anchor bolts and used 4" long 3/8" SS lag bolts to screw through the two holes I had drilled in the bracket and into the post to tie it all together. I used the 12" cardboard forms to build my piers up to my finish floor grade once I had poured a pier footing of 24" sq. I braced the footing with rebar and in the center of the footing I placed 3 pieces of upright rebar 6" apart in a triangle like shape all the way up to within 3 or 4" of the top of the pier.

If you are going to sit your barn on top of piers it seems it would be easier to use the form tubes rather than piers already made because they all need to be the same height once put in place but maybe I'm missing something.

 

[Dutch445]

I ran into the same situation building a house on shale in 1989, the GC called me with
the bad news on how the excavating contractor had ran into this shale and it wasn't going
well. We actually ended up lifting final elevation of the whole house up a few feet (not
a problem as we were on a sloped lot anyways). Then they did pour directly on the
shale in places. Due to the slope, only 1 part of the foundation wasn't down below
frost, the rest was where they wanted it. Everything is still there although I moved out in
2001.
Is it possible to raise your barn elevation a couple feet? May help shed water, and be able to
give more depth to the foundation, poles, etc.

 

[dave1949]

Why did you decide to put the poles into the concrete, rather than mounting them on top of the concrete? You can buy galvanized pole brackets such as MX842 built that are inserted into the wet concrete after filling the forms. The poles will always be dry if you mount them on top. They will always be damp in the concrete IMO.

Or if you intend to pour a slab floor, following what Dutch445 did, you could dig down to solid shale everywhere then build it back up with compacted sand and stone to create an Alaskan or floating slab foundation. You could put in pipes for some floor drains if you want, they are nice to have. I guess that depends on the nature of the shale. If it isn't really bad, I think it will outlast your building by a couple centuries as a stable base for the slab

You would have a choice of standard stick construction--just as homes are built with a j-bolted down treated bottom sill plate with sill sealer under it -- or poles fastened to brackets, if building on a slab foundation. Or combine the methods if you want.

I think what you are planning works too, just throwing ideas out. I've never liked the idea of wood in dirt or concrete but I know it's done all the time. Last year a TBN poster took down a pole barn that was 15 or so years old IIRC, he said most of the poles (they were in soil) were still in real good shape.

A lot probably has to do with the soil type, the site drainage, the quality of the wood in the poles, and the quality of the pole treatment. I guess bottom line, keeping the poles in the air removes all of those variables.

 

[sdkubota]

This will be my last bit of advice...normally in an expansive or potentially expansive type soil you want to increase the bearing pressure on the soil to limit its expansion. A spread type footing will decrease the baring loads on the underlying shale. There are many arm chair quarterbacks and I don't know the specifics of the shales in your area but I have investigated numerous buildings that experiences severe damage due to expansive shales. This is not where I would save money but not hiring someone that is knowledable regarding building these buildings in your area with the given soil conditions. Good Luck!

 

[dave1949]

Good heaven's. The OP is building a pole barn, not the Taj Mahal. The original idea behind pole barns is big space, low cost. They became popular when farm equipment started to out-grow what would fit in traditional barns.

One common sense possibility is to look around the immediate area to see what others have built, how it was built, and is it holding up. If there are neighbors nearby, ask them if they are on your shale and do they have issues or thoughts about it. A county extension agent could tell you how common the shale is in your area.

 

[hkhi]

Why did you decide to put the poles into the concrete, rather than mounting them on top of the concrete? You can buy galvanized pole brackets such as MX842 built that are inserted into the wet concrete after filling the forms. The poles will always be dry if you mount them on top. They will always be damp in the concrete IMO.

I've been going back and forth on poles in concrete vs mounting on top. Mounting on top is easier, but with the drawback of less resistance to racking. Any thoughts on framing modifications to compensate for this? I'm sure it's possible, I just haven't come across it in my research yet.

Most of my neighbors out here have Morton barns. They've drilled through the shale and dropped a combination concrete/wood post. Very nice design, and I was all set to have them build this barn until I got their estimate. ouch.

 

[BeezFun]

Any thoughts on framing modifications to compensate for this? I'm sure it's possible, I just haven't come across it in my research yet.

It's not hard to add diagonal bracing to resist racking, but I'm not sure how you would prevent uplift if you're only 2' in the ground. Pole barns are very light structures, especially if you're using metal roof and siding, and present a large cross section to the wind. You probably know that there is normally some type of modification to the bottom of the poles to prevent pull out: either cleats, or rebar through a hole, or a concrete necklace, or something. And that assumes the pole is at least 3' in the ground. Several folks have mentioned drilling into the shale and epoxying rebar in place, I think that might serve to prevent uplift but you'd probably want an engineer to do the calculation so you'd know for sure how much rebar and how to secure it.

 

[dave1949]

I've been going back and forth on poles in concrete vs mounting on top. Mounting on top is easier, but with the drawback of less resistance to racking. Any thoughts on framing modifications to compensate for this? I'm sure it's possible, I just haven't come across it in my research yet.

Most of my neighbors out here have Morton barns. They've drilled through the shale and dropped a combination concrete/wood post. Very nice design, and I was all set to have them build this barn until I got their estimate. ouch.

Is there anyone around who would do just the drilling? You will have some money in the footing forms and extra concrete too. It's a good local experience clue about the shale if Morton drills to below the frost line.

A pole barn frame is hard to make really rigid without some diagonal braces. The continuous sheathing on a house and the interior walls (both act like diagonal braces) stiffen the frame by quite a bit. A pole barn has lots more surface area and not much in the way of worthwhile diagonal bracing.

Hurricane straps around the trusses to the top of the walls are becoming common everywhere.

Trusses rely on heavy stringers to keep them rigid. There should be zig-zag lines of diagonal stringers on the underside of the top chords and diagonal braces to the gable ends. Also rows of stringers running end to end that keep the bottom truss chords from bowing. The truss manufacturer should specify the minimum number and location of these braces.

If the trusses form a rigid structure, it makes it harder for the walls to move. There is still a weak joint between the top of the walls and the roof, that is the area I would try to diagonally brace to add rigidity. That is hard to do without giving up interior clearance. A side shed with a lower ceiling will act like a flying buttress by putting the bracing on the outside

I can see how putting the polls into the ground or concrete uses the strength of the pole to resist racking. Poles surface mounted on brackets rely on the strength of the bracket, how well the pole is attached to the bracket, and the bracket to the concrete.

If you will sleep better, then put your poles in concrete :laughing:

 

[sdkubota]

Never, never, never attempt to "build" your own roof trusses. Lumber used in them is engineer rated and comes from old growth forests. If you go to the lumberyard and build your own they will collapse. I am 100% certain. Just a tip.

 

[LD1]

Never, never, never attempt to "build" your own roof trusses. Lumber used in them is engineer rated and comes from old growth forests. If you go to the lumberyard and build your own they will collapse. I am 100% certain. Just a tip.

Makes me wonder how anything got done "back in the day" before these engineers??

If done right, you can build your own trusses and not have a single of issues. I am 100% certain of that. I built my own for my pole barn. And dad has a machine-shed that has homemade trusses that has stood for about 60 years now. It most certainly CAN be done successfully