Timber Frame Sawmill Shed span question

[alden213]

Hello everybody,
I've been a member for a little while,but this is my first post. I have a WoodMizer LT15 and I'm planning on building a timber frame structure to house it this summer out of white pine. I'd like to clearspan 24 feet on the log loading side of the mill so I have ample room to maneuver. How should I go about doing this on a minimal budget? The span will be parallel with the ridge of the roof, which will have a 10/12 pitch. Is a steel beam the best way to go? or would it be cheaper to make a gluelam beam or even a monstrous solid white pine beam? Any advice would be awesome!

[flyingparks]

 

 

Is this sort of what you are talking about? I function with drawings and pictures...words not so much. This sketch is very rough, all 8x8's (engineers love me) and no joinery. But if this is the general idea, then yes it is possible, almost anything is.  :D

Large knee braces would help quite a bit. Is your mill on a trailer or close to the ground?

[addicted]

I'm trying to design some sort of cover for a mill as well. Being able to drive through with the mill hooked to a tow vehicle may be a nice added feature.
Also depending on how you load and off load from your mill, the height of this beam should be considered. I usually can load either by rolling or by forks on a loader but monster logs sometimes are better handled with chains lifted from over head with the loader. This changes everything of course. There was a post here a few years ago about a timber truss made for just such a span on a building for a mill. I will try to track it down when I have a moment.

Rusty

[ChugiakTinkerer]

Edit: I originally posted this thinking of my situation, which is a 20' span.  I redid the calculations for 24', assuming a shed width of 20'.

I've pondered this as well and feel that a flitch beam is probably the best option.  You can do it with timber, but unless you have some high grade select you'll probably be looking at something like a 10x14 or larger.

You can check suitable beam dimensions using the calculators in the Forestry Forum toolbox.  Click the link for the red toolbox icon on the left, under all the sponsor banners.  Under Construction Calculators select the Beam and Column Calculators.  On that page you'll want the second link, Simple Beam,Uniformly Loaded (Drop Down Species List).

You'll need to know the design load on the beam.  This is the total for what the roof is expected to hold, and consists of a live or snow load plus the dead weight of the roof itself.  The beam will be holding up half of the roof, so multiply half the roof area by the design load to get the total load on the beam.  Assuming a snow load of 30 lbs per square foot (psf) and a dead load of 10 psf, and a roof area of 240 square feet then you have a load of 9600 lbs, of which 2400 lbs is dead load.

Following the calculator guidelines, try the following:
Under "Total Load" enter 9600
Under "Dead Load" enter 2400
Under "Span" enter 288
Under "Width" enter 9
Under "Depth" enter 14
Under "Species" click Douglas Fir #1 B+S
Click "Show Result"

You'll see that it passes with #1 DougFir, but fails with #2 DougFir.

If you're one of those guys that won't be milling in the dead of winter, you could have a post that gets inserted mid-span as a support when there is snow on the roof.  Then you could probably get by with the absolute minimum that will span 20'.  The minimum design load is 20 psf live and 10 psf dead load, so run the calcs again with 7,200 lbs in the Live Load box.  In that case a 9x14 of #2 DougFir fails, but a 10x14 does just fine.  Note that the deflection test actually passes, assuming you can live with L/240 or less deflection.

[alden213]

flyingparks, Yes, that is pretty much exactly what I am planning. I much prefer pictures as well but my rough sketches are on paper because I'm incompetent with sketchup :D
It will have some big knee braces. The mill is on wheels.

ChugiakTinkerer, We have big white pine around so a giant beam 10x14 or so wouldn't be too much trouble. I don't mill a lot in the winter as I'm usually in school. Maybe I will pour another footer in the middle of the span for an extra support beam in winter as you mentioned just to be safe. Thanks for the tips

[alden213]

addicted, I can see where you'd come across problems if the beam was too low but I was planning on pretty high clearance anyways. I guess if clearance and building height together are an issue then more of a single slope shed roof would work better? I didn't want to do that for my shed because a) I don't like the looks and b) I feel like it won't protect the mill as much as I would like. So I might end up with a skyscraper...

[Crusarius]

I would want to integrate a lifting system into the frame for big logs. But I am also the kind of guy that will find a small amount of space and have to make it better

[Don P]

Knee braces are not typically considered to reduce span. It is better to size the beam for the entire span. For a span of that size I would look to an LVL beam first, your building supply can size that for you. I have a 24' span on the shed roof on the side of our barn in LVL and I sized it pretty close to the limit with the intention of putting in a post in the winter, which I did religiously for the first years. I've looked down there in the snow twice in the past few years and realized I had forgotten to put the post in. I also have an I beam trolley running from the LVL into the barn for pulling engines and such. I intended to only use that when I had the post in place. Yup, sure enough I was lowering an engine back into the truck at one point and realized I didn't have the post in place. Just stuff to think about.

[scrout]

What if you put trusses over the 24 foot length, just use whatever spacing you need for support?
Probably make them with boards cut of the mill too.