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CanadianNorth
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# Posted: 2 Feb 2015 10:07am
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I'm looking for information on site built box beams, but I can't seem to find span tables or anything in terms of strength. I'm wondering how box beams compare to dimensional lumber in terms of strength too.
I'm designing a 2/12 sloop roof (no roof trusses) on a garage (20 x 24) and need to span 20 feet with probably 3 separate beams rather than one to carry the load. Steel is an option but would probably need equipment to lift in place, so would rather use wood, if possible.
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Don_P
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# Posted: 2 Feb 2015 04:45pm
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The APA website... apawood.org, has some info from memory. I don't believe they equalled LVL strengths though so that would be my first trial run. We had some 18" deep LVL's delivered today ~$10/ foot.
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CanadianNorth
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# Posted: 7 Feb 2015 07:42pm
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Thanks Don. I did some more research on the net and found a couple of really helpful sites. I'm surprised how strong these box beams are and hence how long the spans are. I would provide a link but the site I'm referring to is a PDF document.
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Don_P
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# Posted: 7 Feb 2015 10:50pm
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I don't think there'd be a problem posting the link(s), I'd like to read it.
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CanadianNorth
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# Posted: 8 Feb 2015 09:38am - Edited by: CanadianNorth
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Try this link:
http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CB0 QFjAA&url=http%3A%2F%2Fwww.forestryforum.com%2Fboard%2Findex.php%3Faction%3Ddlattach% 3Btopic%3D27057.0%3Battach%3D1494&ei=l3TXVN6FKYjFggTt5ICQAQ&usg=AFQjCNH19xAPl2w0WfUhx UXCXCOh5wmexA&bvm=bv.85464276,d.cWc
If you want to see the math:
https://law.resource.org/pub/us/code/bsc.ca.gov/sibr/org.apawood.S812.pdf
And here is a group of engineering students testing the strength of a box beam:
http://srt251group10.tumblr.com/
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Don_P
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# Posted: 8 Feb 2015 02:31pm - Edited by: Don_P
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Those are the documents I was thinking of from APA. At 20' span pay attention to the sections talking about splicing the flanges in the second document. The tables are for unspliced flange members, there are reductions and details for spliced members. There is a ton of nailing involved. I think in the thread that lead up to your first linked document the fellow did build with plywood box beams, they worked but apparently so did he. It's hard to beat just setting a nice straight and true LVL if it'll work.
I am curious to see how they compare, what have you come up with size and costwise?
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CanadianNorth
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# Posted: 8 Feb 2015 04:43pm - Edited by: CanadianNorth
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I agree that engineered lumber is precise, reliable, and easy to use. And, as you pointed out, there is a lot of labour involved with nailing in the construction of a box beam. May need a nail gun to not just save your arm but put the nails in consistently as well so as to not disturb neighbouring nails that a hammer would do with each impact. I would use construction adhesive as well, and clamp all pieces during construction to ensure the tightest of bonds between all pieces.
I'm in the early stages of design, so I have done no costing yet. But I would imagine there's not a lot of difference, once labour is factored in. But I do like the challenge of the box beam. Steel looks good too, with the exception of getting it into place by hand. But I think that can be overcome with a little bit of ingenuity. Come-alongs are handy tools.
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Don_P
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# Posted: 8 Feb 2015 06:00pm
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We just rolled a W18x63 x30' into a house on pipes and lifted it with come-alongs to support the second floor and roof. Just figured it all out ahead and went slow and steady.
Safety monitor story; What tore out the first rotator cuff muscle on my arm was a come-along in an overhead lift. Make sure the catch pawl is fully engaged each stroke, visibly look at it and make sure it is fully seated. With mine it caught a tooth on the edge of the pawl, I assumed it was engaged and released to get the next bite. The pawl slipped off of the edge of the tooth and with the load, when the next tooth came around it bent the pawl out of the way and dropped the '35 Dodge. But I've lifted alot of stuff with them.
One nice thing with an I beam with extra capacity, you can mount a trolly on it, hang a hoist from that, lift engines out, roll over and set them on a dolly.
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