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Spanning 20ft

Started by emery, September 15, 2019, 11:54:41 PM

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emery

I'm needing to span 20ft but can only mill 16ft. I'm thinking of using a whole log it's beetle killed spruce.
I have plenty of them standing dead for several years now.
If I'm to use one. How big should it be for snow load? I'm in south-central Alaska.

Don P

Hey emery,sure. There is a log beam calc in the red toolbox, bottom of the column on the left of this page under Don P's calcs> beam and column calcs.

You didn't give enough info to answer the question but look over the calc, you might not need more than that.

DDW_OR

following: i am also doing a 20 foot clear span for my 20x32 work shop

i tried to use that calc
I am VERY GREEN, and could not understand how to put in the numbers.

having a few examples would be VERY helpful
"let the machines do the work"

Don P

Do a rough sketch so I can see how the roof lands on the beam. What is your snow load and species of the beam?

DDW_OR

@emery
you could mill the first 16 ft then use a saw to remove the slab
then shift the log to finish the cut
"let the machines do the work"

Autocar

I spanned twenty feet this past summer using 12 foot white oak and spiked them togather at 21 foot and then on the long end spiked another one on the side making it a 4x6x21 feet . Then when I set the beams i flipped them end for end as i sat them four inches then the next would be two inches . 
Bill

Don P

That sounds like the kind of thing I spend a lot of time hoping to help people avoid  :-\

Sauna freak

Is this a flat span to hold tension/compression, a rafter span for load, or a simple roof span to do both?

If a t/c span with no vertical load, you could make a composite with 2x 12 foot lengths with a 4' overlap or a full composite beam.  If a simple roof, you'll need 20's.  2x10 framing or 4x8 or equivalent round timber would meet code in Northern MN on a 24" C spacing 3/12 pitch or greater.  Need more information, there is probably a good method to complete your project with 16' or shorter lumber.

If a rafter spanner, you could scissor truss with 16' or shorter and achieve equal or greater support.

Don't know your milling setup, but assuming a static band or ripsaw mill.  A small Alaskan chainsaw mill may be the best option to mill longer spans.  You can fabricate whatever length starter rail you need.  If you already have a 60CC or bigger saw, a small one will be less than the cost of 4 rafter boards.
Sauna... like spa treatment, but for men

Don P

Notice the time stamp of the original post.
I noticed he only made one post so just went and looked at his profile
Last Active:September 15, 2019, 11:53:42 PM
Don'cha just love people who pop in, ask one question and never even bother to look to see if it was answered  ::)

Don P

Whoops, I wasn't shouting just making an observation. The cut and paste of his time stamp must have blown the font up :D.

thecfarm

I've noticed that a few times too.  :(
Model 6020-20hp Manual Thomas bandsaw,TC40A 4wd 40 hp New Holland tractor, 450 Norse Winch, Heatmor 400 OWB,YCC 1978-79

Nebraska

I, and I bet most all the group still appreciate  all the  information   you dispense.  Even if  folks don't come back to look, somebody else benefits down the line.  @Don P 

SwampDonkey

Happens. Could be 10 difference reasons why. ;)
"No amount of belief makes something a fact." James Randi

1 Thessalonians 5:21

2020 Polaris Ranger 570 to forward firewood, Husqvarna 555 XT Pro, Stihl FS560 clearing saw and continuously thinning my ground, on the side. Grow them trees. (((o)))

firefighter ontheside

Yes it seems a little rude to ask a question and let numerous people go thru the effort of typing out a nice answer, but never to come back and read the answers or say thanks.  It happens on the woodworking forum that I'm on too.  
Woodmizer LT15
Kubota Grand L4200
Stihl 025, MS261 and MS362
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1998 Dodge 3500 Flatbed

Gary Davis

there is an article in the forum showing how to cut a beam longer then your saw

farmfromkansas

In the days before inspectors had manufactured beams available, I used to stack 2x12's, one on top of another, then glue and nail 3/4" plywood on both sides.  Those will hold, but I did not splice the 2x12's. 
Most everything I enjoy doing turns out to be work

Don P

That makes an unquantifiable beam, no telling how strong it is. The problem is locking up the horizontal shear between pieces if you are actually trying to load it as a 24" deep beam. An engineering professor said the conservative way to look at that situation is not as say a 2x24 but assume that they are acting as if side by side, a 3x12. When you're in that kind of bind, as mentioned we have LVL's nowadays, the material itself is much stronger and stiffer than solid wood, basically about twice the bending strength and a third stiffer in the same sizes and I have used it as wide as 24" deep, you can get big ones. Right now with building material prices spiking also check out steel. 

farmfromkansas

I have used I beam as well, just drilled holes top and bottom and bolted boards on, then set the beam in place and nail it.  Sheetrockers had nailers so they could  wrap the thing.  Years ago a lot of framers built poor beams, and they would sag.  I have repaired some, by just jacking the ceiling up and adding more plywood and lumber. Much easier to do it right in the first place.  Also discovered a way to build a 16' garage door header that did not sag,  would put a 2x12 at the bottom of the header, and a 2x4 at the top of the header, right under the plate, then lay sheets of ply from the top plate to the bottom of the 2x12, glue and tack to the lower 2x12, then lay the other 2x4  at the top and another 2x12 at the bottom with glue, and then nail throught the whole mess, also lay short 2x4's vertical between 2x4 and 2x12, and nail up the whole mess.  Be sure to jack the header up so it does not sag, or the header will bow in when the wall is stood up.  Most of my experience was before they came out with these LVL's.  One thing I like about those plywood beams, is that they make great hip and valley rafters. I built about all stick framed roofs. We did get to using trusses on 3 car garages.
Most everything I enjoy doing turns out to be work

Don P

One thing to remember when building a pony wall on top of a dropped header (don't do it) is that a longspan dropped header fails by "laying over", the top bowing out of plane under load. Most engineered beams and steel I beams will have a note that says something like "max distance between lateral support". That is something holding the top edge of the beam straight. The classic example is a big garage door opening dropped well below the ceiling. The beam should be up high and the pony wall hanging under it is better than a dropped beam with a pony wall on top. Here's an article on it;
https://i-joist.org/wp-content/uploads/2018/05/WIJMA-Dropped-Header-Design-Guide-11-7-07.pdf

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