Pole Barn Construction

[lovethecold]

I am preparing a soils report for a pole barn. The dimensions are 72' x 200' in plan view. I am planning to give 2000 psf for net allowable bearing pressure. I am assuming a maximum column load of 50kips and no load bearing walls. Soil strength won't be an issue, nor should settlement or differential settlement.

Mostly I am wondering, how are these buildings typically constructed. What loads are typically placed on the columns, and what are the maximum loads a pole barn could have.

All the salesman could say is most are constructed with 3 member laminated 2x6 posts about 6' to 7' deep with 18" to 30" diameter coulumn pads.

Thanks for the help.

 

[msquared48]

Salesmen will say anything to get the sale. Posting here to get an informed opinion is a good step. However, the following would help:

1. What is the eave height and roof slope?
2. Is the structure open or covered?
3. Are Knee braces an option?
4. What is your design wind speed for your area?
5. What is the exposure category?
6. What are the soils like?

My initial reaction without any of the above information is that the (3) 2X6 will not be enough, and the 2000 psf bearing will not be enough for the 50 kip max load. The engineer will have to extend the pole footing deep enough to get an allowable bearing high enough to support the load.

Mike McCann
McCann Engineering

 

[MiketheEngineer]

I agreed w/ Msquared...

Typically pole barn trusses (assuming wood) are at 8' to 10' on center.

Say you have 20 psf live load and 15 psf dead load at 10' oc - then your post reaction would be 10' x 35 psf x 70' /2 or about 12,250 lbs. There are factors that might raise this but 50 kips seems awfully high.

Your column pad (at 50 kips) would need to be 25 sq ft or 5'-7'' in diameter!!! Three or four 2x6's or 2x8's are often laminated and used as columns depending on height and load. But 50 kips would blow 3-2x6's out.

I think a closer look is warranted.

BTW - IBC2003 only allows for 1500 psf if no soils tests are done.

 

[lovethecold]

Thanks for the responses. I do not know what loads a 3 2x6 posts could take, but am certain they could not bear 50 kips. It is my understanding that they will typically use wood, but may use steel columns. I have been told that some wood posts may be 16" in diameter. We do very few of them.

I am curious about how a structural engineer looks at these buildings and what considerations go into their design. I think it would make the soil report easier to prepare if I had a better understanding. As I mentioned, the only person I spoke with was a salesman, and he only knew the design was based on 2000 psf bearing capacity and that he was supposed to get a soil report.

Is there a good book on designing wood framed structures? I missed that class (took other classes).

Thanks again.

 

[SlideRuleEra]

See "Pole Building Design" (free, zipped .pdf download) on this page of my website

http://www.slideruleera.net/miscellaneous.html

http://www.SlideRuleEra.net

 

[MiketheEngineer]

Dr. Frank Woeste (spell?) from Virginia has written many articles on this subject.

Also check the

http://www.nfba.com

website (National Frame Builders Association)

http://www.apawood.com

or org is also good

 

[lovethecold]

Thanks for the links. SlideRuleEra, your site has now been favorited, thanks.