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25ft Span Post Free: Milling My Own Beam Need Help!

Started by jemmy, October 06, 2017, 12:20:15 AM

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jemmy

I need to span 25ft with out posts in between. This is a building for a sawmill where I max out at 25ft in length of cutting capabilities.  For this I plan on cutting a beam out of white oak to span the distance. I can cut 24"x24" but I don't think that would be necessary, but I know these things start getting goofy with snow loads and high winds. This building will need to be able to handle Ohio snow loads, and winds in excess of 70 mph (very rare but they come sometimes haha)... This span will be towards the east and even if a storm manages to flow towards the west it is shielded by heavy woods. The perpendicular distance will be between 20 and 30 ft. I have a few other ideas with a separate set of calculations and way of thought. I am just looking for some general rules of thumb and if what I am talking about is practical. I feel like a 24"x12"x25' would be sufficient (if not over kill). I have attached a photo of the building and the beam in question. The picture is not perfect but your should be able to give a solid visual. If you just want to drop your 2 cents any advice is greatly appreciated!  And lastly I have given some thought to the idea of buying a metal beam of some form.... That will obviously exceed the cost of the milling my own beam.


https://forestryforum.com/gallery/displayimage.php?album=7962&pid=234196#top_display_media
Plan for the worst, hope for the best, and take what comes with a grin. - Grandpa Chuck

MbfVA

The more information you put in your profile, where you are, what your equipment is, all that kind of stuff, the more we can help you.   I'm rather new, so it probably won't be me 🤓, but I know what these guys need, so I'm getting ahead of the game by recommending that you fill out your profile.

That way, when the ones in the US wake up, the bright ones who went to bed on time (at least in EDT), unlike me, they'll see what they need to start helping.  Also, general advice only: please always give avoiding typos your best shot--they can really screw up a message, and can prevent someone from finding your subject using search, later on. Siri, my often unhelpful digital assistant, tries to make a monkey out of me every time I use it.  Your typos were very minor, but I thought I'd rant about it anyway, no offense intended to anyone.

If you're lucky, someone like Don P or Jim Rogers will show you how to use the forum calculation tools to size the beam and other components.  If you have sketchup make, the freebie, that's a great way to draw something in a hurry.

A 24 in sq beam would be a heck of a beam.   I wish we had a lot of trees like that on our property. You might be in more danger thereby from that beam falling than from a snow load, imho.  Yeah, I'm sorta kidding.  BTW I did see Ohio mentioned in there--I went there back, just W of Pittsburgh, in June to pick up my Peterson saw mill from a guy who was selling it because of an accident he had.   Good luck!
www.ordinary.com (really)

rjwoelk

Why not go to your local truss rafter guy and get a quote on a truss beam to put under there. You can then use that big 24x12x25 in a much better way. If you go to the timber frame thread you will find that it is not recommended to exced 16 ft span with a solid beam.
Another suggestion would be to use truss rafters and go 30 ft wide. Then you would have room to put your mill on the end. If you need to come in make smaller doors on the side. The benefits of going on the end is if you are milling and its raining you dont have it all coming off the roof. Unless you put gutters on. Just some thoughts.
Lt15 palax wood processor,3020 JD 7120 CIH 36x72 hay shed for workshop coop tractor with a duetz for power plant

ChugiakTinkerer

Looking at your photos you're clearly in country where snow load is a concern.  A 25' span is pretty long even without worrying about snow.  One thing that some sawmill shed builders have done is to disregard snow load worries and just put in a temporary post during the winter.  If you're not milling in the winter that might be an option.

The way to determine what size beam you need is to start with determining your load.  The minimum design load for a roof is 20 pounds per square foot (psf) live load and 10 psf dead load.  That totals 30 psf, and you need to multiply that by the square footage of the area of the roof supported by the beam.  It looks like 15' for half the building depth, times 25' for the span to equal 375 sf.  The total load then is 30*375 = 11,250 lbs.

On the left side of the forum pages are the sponsor links, and at the very bottom is a link to the toolbox page.  If you click on that, then click on the Beam and Column Calculators Link you can then select the second link on that page, Simple Beam,Uniformly Loaded (Drop Down Species List).

Using this calculator you can input the parameters of the beam and the load requirements and see if it is adequate for your needs.  I input 11,250 lbs for load and 3750 lbs for dead load and selected Whit Oak B+S #2 for the species.  With those values the 12x24 beam passes easily.  You can in fact make it narrower down to 6" x 24" and it still passes.

This however is with minimum design load.  If you need to withstand a snow load of 50 psf, that kicks your total beam load up to 22,500 lbs.  In that case a 12" x 24" is strong enough, but just barely.

The grade of the beam timber is more critical than beam dimensions in this calculation.  I selected white oak #2, but if you have a good selection of trees and can find a log that will yield a #1 or select grade timber then the beam load bearing capability goes up substantially.  Using that calculator, a select white oak beam 12x24 can withstand a load of 37,500 lbs, which equates to 90 psf snow load.

I should qualify all this by stating that I have no particular expertise in timber framing or structural engineering with wood.  I'm just a guy who has spent a couple years trying to figure out the right beam and post dimensions for a cabin.  You should do all these calculations yourself, and verify with an actual expert that you're on the right track.
Woodland Mills HM130

jemmy

ChugiakTinkerer thank you, this is exactly what I was looking for! I have spent some time looking around for the right calculators and nothing really suited what I was looking for. Thank you for mindset as I look at the building. There's a couple other questions I will post later, this build is going to be pretty unique, and involve some crazy dimentions. Thanks again for your help!
Plan for the worst, hope for the best, and take what comes with a grin. - Grandpa Chuck

ChugiakTinkerer

You'll notice the calculator is one that Don P posted.  He's the one to credit for any benefit my post may have been for you.  If you are lucky enough to get his insight on your project I would take it as gospel.  Or at least trustworthy enough for further verification! :-)

Good luck, and post more sketches.  Also, if you update your profile to show your general location, folks might have a better idea of how to be helpful regarding snow wind, etc.
Woodland Mills HM130

Mad Professor

Have you considered a swing beam?  Like they used in old barns so they could turn around wagons without a post in the way?

These are from one of Richard Babcock's books.  Before he passed He gave me the O.K. to scan and post his works with proper attribution.

This is the German barn, he moved from NY state, to Wolftrap Performing Arts Center.  I'll have to dig out the book (Old Barns in the New World? Barns at WolfTrap?)  and will post ISBN. I think the sketches may have been done by Jack Sobon?








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