# load capacity of wood columns



## jklingel (Jul 30, 2009)

Does anyone have a reference for the load that various wood columns (rounds) can carry? My searching on the Net gives me all kinds of info, but nothing I can understand; too much engineering language. I just want to know how many POUNDS (not "kips", whatever they are) a 10' peeled aspen log will carry when stood up, unsupported, and is 10' long, etc. Info for store-bought 8x8's, etc, would be nice, too. Thanks. john


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## jebatty (Jul 30, 2009)

kips = 1000 pounds. You probably found this (douglas fir-larch), not aspen.

Load Capacity


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## stee6043 (Jul 30, 2009)

jklingel said:
			
		

> Does anyone have a reference for the load that various wood columns (rounds) can carry? My searching on the Net gives me all kinds of info, but nothing I can understand; too much engineering language. I just want to know how many POUNDS (not "kips", whatever they are) a 10' peeled aspen log will carry when stood up, unsupported, and is 10' long, etc. Info for store-bought 8x8's, etc, would be nice, too. Thanks. john



10 foot tall and unsupported????  Yikes....


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## jklingel (Jul 30, 2009)

Thanks for the replies. I figured kips was kilo something. Exactly what are the initials for? Just KIloPoundsS? Yes, it was for doug fir. As for unsupported, yes, if I have my nomenclature correct. I want to have a 10' clear height for a room, so I'll be walking around some naked (unsupported) posts. I don't see that as particularly odd, but maybe 10' is pushing it????


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## SolarAndWood (Jul 30, 2009)

What are your spans?  Why not beef up the beams and eliminate the posts?


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## jklingel (Jul 30, 2009)

I've looked at larger beams, but there is always a point where increasing beam size gets prohibitive, either because of cost or beam height. Cutting a span into pieces, though a PITA to walk around a post or two, is sometimes all you can practically do. For right now, the "span" is 42'. I am adding a roof along the side of my house so we can park there, out of the weather. I'll be putting 4 posts along the length, each side, and running a beam on top. The width, 12', will be spanned w/ 2x10's, 16" O.C. For this job, I am sure that 6x6 posts would be very adequate, but for down the road I want to know what 8" and 10" logs will carry.


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## stee6043 (Jul 30, 2009)

What is it you're buidling?  Perhaps we're mixing up the words.  The material you use to support vertically are your posts.  Anything going horizontal is a beam.  For posts typically you'd want 6x6 for heights reaching 10'.  I have 9' height on parts of my deck being supported by 6x6x16' posts buried 4' in the ground with proper footings.  For interior work you'd usually use steel floor jacks designed to support "buildings".

10' spans are not particularly long if you're talking about beams depending on the size and loading....when you said "post" and "unsupported" in the same sentance I envisioned you standing posts on the ground and not anchoring them or not having any kind of attachment to the ground.  Perhaps you were talking about beams?


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## jklingel (Jul 30, 2009)

Words. If you use the right ones in the wrong place, it sure confuses things. Sorry about that. For my "roof", for lack of a better term, which will be 42' long by 12' wide, I will use the aspen logs as columns to support a 42' beam (4 logs under a 42' beam). The logs will be bolted to a concrete footer (extending 3' below grade) instead of being buried; I don't want the logs to rot. I'll have some serious steel well embedded in the concrete and well anchored to the logs. Certainly, 6x6s would work fine, but then I'd have to buy them; logs a free.... sort of.... if I ignore my labor. By "unsupported" I meant that the logs will have no lateral bracing to minimize flexing under load; that is my understanding of what an "unsupported column" is..... but, I could be confused, and more than likely a term like "unbraced" or "un-wtf" would be better. Dunno. I hope that clears up the confusion. Basically, I'm building a deck and replacing the typical 6x6s w/ logs. Down the road, I'd like to know what load these logs will carry, if properly supported and properly braced against lateral deflection. Man, I gotta take a nap and clear my head for the next job.... j


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## stee6043 (Jul 30, 2009)

Hah...makes much more sense now.  Seems you've got a pretty good idea what you're up to.  My first question based on your new description would be - are you sure about 36" deep footers?  I'm in mid-Michigan and code is 42" deep.  If you're in Alaska (I'm assuming, Fairbanks?) I would think you would need to be deeper than us here in MI.  Required depth is more a function of your frost line than it is how much support you get from going deep.  If frost gets below your footers you will have some real problems.

Your support for lateral loads is your beam.  Make sure you have a good connection between the post and the beam and all is well in the world.  Staggered bolts (5/8" bolts perhaps) help to increase rigidity at your connections...knee brace at the top if you really want to go crazy someday.  But that should not be necessary...


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## jklingel (Jul 31, 2009)

Stee: It sometimes takes me a while, but I can usually get it all explained clearly. Next time, I'll send in a sketch. Yes, the 36" footer should raise flags, and code here is also 42" (to the top of the footer). However, I cheated 35 yrs ago and put my deck posts down only 2', and so far, so good. I also built my addition, about 25 yrs ago, slab on grade, no foundation wall. I get by, I feel, because I work hard at sloping the earth real hard and fast away from any structures. Maybe I am just lucky, but dry dirt does not heave. That said, my house has a "by code" foundation wall, and the new house will go down 48" because it is going to be about 90' long. That's a whole new bag, though. All that said, I can not guarantee that my deck, on the side 12' from the house, does not float up and down a tad. After 35 yrs it is no longer "perfectly" level, but you have to work at it to notice. So, I think I'll just go down 3' on the new "deck", though if I hire my neighbor's Bobcat w/ a hole driller, then 4' won't hurt so much. I don't like going beyond 3' with a regular old post hole digger, as you have to dig a trench so you can open the handles to bite, etc; major PITA! Thanks for the input; suggestions/questions are always welcome. john


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## DiscoInferno (Jul 31, 2009)

I recently looked up the conversion from square to round because I want to build a woodshed from all the dead balsam fir poles on my property.  If I read what I googled correctly the diameter of a round post needs to be 6/5 or 1.2 times larger than the side of an equivalent square post.  So a 6x6 post that is really 5.5x5.5 is equivalent to a circular post with a diameter of 6.6".  

If you use round beams (horizontal) and want to compare to rectangular beams it's more complicated because there strength goes as thickness x height squared.  Thus round logs make better posts than beams.


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## jklingel (Jul 31, 2009)

Disco: Thanks. That makes approximate sense, as the ratio of the area of a square, with side 2r, to that of a circle w/ radius = r, is 4 to 3.14. Surely there are other factors involved besides purely area, too.


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## DiscoInferno (Jul 31, 2009)

It's not area, as strength was given as proportional to r^3 for either circular or square (with different scaling constants) and w x h^2 for rectangular in a horizontal configuration.  I confess I didn't actually look over the math to see how it was derived.  It was a google books excerpt, the underlying theory might not have been available or even in the book:

http://books.google.com/books?id=hF...k_result&ct=result&resnum=1#v=onepage&q=round square beam load&f=false

Looking at it again, all the calcs were for beams and not posts, although I can't imagine there is much difference in the relationship between square and round for posts.  (Any MEs on the board are welcome to contradict me.)


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## jklingel (Jul 31, 2009)

As far as I know.... Yes, for beams, the load capacity is inversely proportional to the cube of the span. For posts (columns), it is a matter of material, or square inches. That book you referenced was very informative, btw. Read page 29, section 44 (if I recall. It is right above the section you referenced). That section discusses calc'ing the necessary post diameter with a given load. The book looks "old", too. Good to see that math and physics worked back then; dang stuff may NEVER go out of style! Thanks. john


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## jklingel (Jul 31, 2009)

Good God. Here it is, 0100 hrs, and I'm reading this book. Problem is, I am reading it backwards, as the more I scroll up the more good info I find. I may just have to up and buy the thing.... j


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