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Pine Center Post for cabin

Started by OH Boy, March 02, 2015, 08:37:36 PM

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OH Boy

We needed an 18 ft log to use as a post for the center of our cabin, and had a nice White Pine log in the log pile. Its been laying 1 year, and the bark is mostly falling off, with some help from the goats.

It is 12" at the base and tapers to about 10" at the top. I'm planning to use it in the dead center of a 24 ft square cabin, going up through the loft floor and supporting the center of the roof beam's which will be 2 x 12 x 12.

what I'm wondering : is a 12" Pine log strong enough to support the loft floor and roofline? it will support the loft floor on double 2 x 10 joists at 12 ft out from any wall. kind of hard to explain. I'll try to upload pdf's of my sketchup drawings after I draw the log post in.



 

WmFritz

That photo is great.   :D

I didn't know Poston's kin worked for bark. ;D
~Bill

2012 Homebuilt Bandmill
1959 Detroit built Ferguson TO35

Jim_Rogers

Put the sketchup file in the file section where there is more room to upload it.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Jim_Rogers

The next thing you have to look at is what is the load coming down from the roof?

What is the load coming from the loft?

Can you figure that out?

If you have a 10" round log you'll need to figure the square inches of area. Then you can multiply that by the value of eastern white pine compression parallel to the grain of 325 lbs per square inch. So for example if the piece was a 10x10 it would be 100 sq inches. Times 325 = 32,500 lbs it could hold up.

You need to figure your loads and do the math if you can.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

OH Boy

Thanks Jim,Just what I was looking for.

I'll flush off the ends of the log and figure how to measure sq. in. for a circular area, then estimate roof weight and loft floor weight. Since its a single log holding both roof and loft floor, I guess I better add them together for the total.

Just wondering since this is going to be in the center, will it only really carry half of the load, and the wall studs carry the other half?

Couldnt find the file upload button, so took a picture of my sketchup, might show what I'm trying to explain.


 

Ljohnsaw

Quote from: OH Boy on March 02, 2015, 09:30:25 PM
Thanks Jim,Just what I was looking for.

I'll flush off the ends of the log and figure how to measure sq. in. for a circular area, then estimate roof weight and loft floor weight. Since its a single log holding both roof and loft floor, I guess I better add them together for the total.

Just wondering since this is going to be in the center, will it only really carry half of the load, and the wall studs carry the other half?

The area of a circle is Pi x R^2, so for you 3.14 X 5^2 or about 78.5 sq inches.  Multiply by 325 (per Jim) and you have 25,512.5 pounds of support.  That is the minimum, the bottom is 12" so it will support a bit more.  The roof calc you need to figure out the load of the wood rafters, sheathing, roofing material, your snow load (live load) and then add the County's dead load value (typically 20 lb/sq-ft or PSF).  Do a rough sketch of the roof area - the post will be supporting the load halfway to any other supports, so a rectangular area in the center.  Multiply this area by the total load/sq-ft and that's how much you need to support for the top section.  Do the same on your loft.  The live load will be something like 30 PSF and dead load of 15 PSF.

On my cabin, I had 12' spans in every direction (you need to account for the slope of your roof to get the actual sq-ft) and my posts (8x10) have to support around 20,000 lbs. (rated at 26,000) each supported by pads that are 4½ foot square, capable of holding 30,000lbs.
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Ford 545D FEL, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/36" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

Jim_Rogers

What ljohn said is right.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

OH Boy

Gentlemen,
extremely helpful and I really appreciate your knowledge. who knew there was so much math in engineering?

I measured my log after flushing off the ends and it is only slightly smaller than my eyeball estimate, came out at 9 1/2 in at the top, and 10 1/2 in at the butt, so not a lot of taper.

using the formulas I came up with estimated load support at 23,010 lbs for the smaller (top) end, and 28,112 lbs for the butt end.

also figured the load estimates based on my plans, and used absolute top end snow load, dead load on the roof, and dead and live loads for the loft floor, and came up with estimated total load weight from roof to butt of log on bottom floor at 18,092 lbs.

if I remember how to do the percentage right, even using the lower load support number of 23K, I'm at 79% of possible estimated capacity for the post, 64% of the higher estimated capacity.

the more I get the bark peeled ( doing it with a 1" wood chisel, good thing its coming off nicely) and see the log is in good shape, no rotten spots, natural structural defects, ect, I feel pretty comfortable with using this size log for a support post.

thanks for the info.

jander3

 I rough calculated loads; however, in the end, I went with, "Big enough, she will be alright!"



  

 

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