Plywood
Printed From: Unofficial Allis
Category: Other Topics
Forum Name: Shops, Barns, Varmints, and Trucks
Forum Description: anything you want to talk about except politics
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=194775
Printed Date: 08 Jun 2025 at 4:45pm
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Topic: Plywood
Posted By: Steve A
Subject: Plywood
Date Posted: 23 Apr 2023 at 7:27am
| How do you look up the shear strength of 3/4 plywood used vertically? In this example using 12 inch X 8 ft pieces of plywood laminated side by side in a staggered arrangement screwed and glued to build a beam? I realize different grades are going to be different strength. Just looking for something like a span table to get a general idea. |
Replies:
Posted By: DMiller
Date Posted: 23 Apr 2023 at 7:39am
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Will be a engineering basis for that but will take considerable math to get there that I do not possess. For every laminated component plus layers of lamination with cross graining and compression of glued structure. Gets really complicated really fast. Lami-beams are generally three to five times stronger than a similar dimension solid wood piece.
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Posted By: Steve A
Date Posted: 23 Apr 2023 at 7:55am
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Thanks for the reply. I realize it would be a matter of engineering and involve shear tests to get to the exact limit of capacity depending on how you use it. I can find multiple references to what a square foot will support horizontally, but I haven't seen anything when used vertically. I assume its also possible they may print it on the side of the board or have it available from the manufacturer too. Seems likely they must have some type of industry rating or standard but I haven't found it. |
Posted By: NEVER green
Date Posted: 23 Apr 2023 at 8:43am
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Will it be a lot cheaper to build your own??? ------------- 2-8050 1-7080 6080 D-19 modelE & A 7040 R50 |
Posted By: fixer1958
Date Posted: 23 Apr 2023 at 8:47am
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What I have in my garage and basement is doubled up 2x12 laminated. Support every 12'. |
Posted By: jaybmiller
Date Posted: 23 Apr 2023 at 8:50am
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how long a beam ? what does it have to support ? up here, north of the 49th, $64 buys a spruce sheet. That means each 12" wide strip is $16 !! There are cheaper, easier ways to 'build a beam', once we know the span. 2by4 floor trusses, LVLs, TGI, etc.... ------------- 3 D-14s,A-C forklift, B-112 Kubota BX23S lil' TOOT( The Other Orange Tractor) Never burn your bridges, unless you can walk on water |
Posted By: Coke-in-MN
Date Posted: 23 Apr 2023 at 9:02am
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When you say vertical is tis for compression strength or as a diagonal and used in loading like a floor weight ? chart of laminated lumber shear or compression https://www.google.com/search?q=chart+of+laminated+lumber+shear+or+compression&rlz=1C1CHWA_enUS627US627&oq=chart+of+laminated+lumber+shear+or+compression++&aqs=chrome..69i57.25987j0j15&sourceid=chrome&ie=UTF-8 https://extension.okstate.edu/fact-sheets/strength-properties-of-wood-for-practical-applications.html" rel="nofollow"> Strength Properties of Wood for Practical ApplicationsOklahoma State University https://extension.okstate.edu › fact-sheets › strength-pr... https://extension.okstate.edu/fact-sheets/strength-properties-of-wood-for-practical-applications.html" rel="nofollow"> This fact sheet summarizes some of the basic concepts related to mechanical characteristics of wood, including viscoelasticity, compression, shear, ... https://extension.okstate.edu/fact-sheets/strength-properties-of-wood-for-practical-applications.html#:~:text=Viscoelasticity,-In%20contrast%20to%20metals%20and" rel="nofollow - Viscoelasticity · https://extension.okstate.edu/fact-sheets/strength-properties-of-wood-for-practical-applications.html#:~:text=Compression,-Compression" rel="nofollow - Compression · https://extension.okstate.edu/fact-sheets/strength-properties-of-wood-for-practical-applications.html#:~:text=MOE%20and%20MOR,-In%20the%20case%20of%20bending" rel="nofollow - Moe And Mor ------------- Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something. "Challenges are what make life interesting; overcoming them is what makes life meaningful." |
Posted By: DMiller
Date Posted: 23 Apr 2023 at 9:34am
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Remember, a 2x12 laid flat sags and bounces, on edge stands firm, Three 2x12s laminated make a stronger beam than a 6x12. Steel I Beam will bounce or bow with applied weight, has to or will fracture. Two C Channels same center width as a I beam will carry more weight with less flange and will bounce/bow less.
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Posted By: Steve A
Date Posted: 23 Apr 2023 at 10:28am
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Thanks folks. I found what I was looking for. The rest of the story: Daughter and husband bought a ranch style home--1989 construction-- and want to remove a section of wall between kitchen and dining room. Both are mechanical engineers; so is his brother. Very calculating, careful people. Their first idea was a barn beam under the trusses and exposed. They disgarded that because it took up ceiling room plus couldn't get engineered strength rating of an old barn beam. Second plan was placement of a beam above within the trusses with steel hangers to the center of the trusses to provide support from above. He has since found that the company that makes the truss rated them high enough that they don't think they need to add a beam at all. They are waiting on a civil engineer to inspect and approve it. When they were contemplating the beam-inside-the-truss I suggested possibly fabricating it in place by laminating pieces of 3/4 plywood, since it would be easier to put 8 ft X 12 or 16 inch sheets up there than sliding a 20 ft pre made beam in and removing the siding of garage end wall to do it. Whatever they do is up to them; I'm staying out of it and watching the process. My question is pure curiosity to see if what I was thinking was feasible, in the event that I ever buy a house and decide to do a similar remodel. |
Posted By: DaveKamp
Date Posted: 23 Apr 2023 at 11:11am
Woah, Steve... hangon here... I think you've got some terms mixed up here. There's different types of loads, and they aren't interchangable in terminology. Shear loading, and columnar loading occurs, but is not in the same realm as beams and spans. If you're suggesting making an I-beam shape using laminated plywood, you need to know exactly how you'll be affixing and loading the I-beam to determine wether it will sustain any shear or columnar loading. This is why manufactured microlam beams are documented for very specific use, not general purpose loading. Most metallic structural shapes (i.e. rolled steels, extruded aluminum, etc) will be extremely predictable in general-purpose loading calculations because the forming will result in predictable character (stress/strain/deformation/yield) as well as ultimate failure, and any grainulation which occurs can be included. [aluminum is a very highly grained metal, so loading stresses always need to respect natural grain] Plywood, however, is a composite, and does NOT have any enforcement of grain, and unless you're using a marine voidless, you won't have predictable adhesive or cavity quality assurance. So the only 'safe' way to build, if you're building based on sandwiched plywood, is to use considerably more material, and expand it's operating area well beyond the stress centers. Note- I'm not saying it cannot be done... I've got a local pal who's an aeronautical structural engineer, his grandfather built DeHavilland Mosquitos... I'm just saying that the question you're asking doesn't fully make sense... it's like asking wether you walk to school, or carry your lunch. Illustrate what you're attempting to do, explain what load you're trying to support, I'm absolutely certain we can figure it out in a way that you can get a sufficient answer. ---------------------------------------------------------------------- Duhp, I see that you got your answer fast. Good. More than likely, if it's a ranch-style house, that wall between is not a 'load bearing' structure, so the only serious concern is wether the walls on each end lose any rigidity as a result of the loss of that third dimension of support inside. IF they were to apply structure above the ceiling to recover that rigidity, it'd be a circumstance of balance and compromise. In the ceiling, it'd be acting as just a stiffener of the walls below, and the attachment method would be the weakest point, as all the stiffening action would be concentrated at it's attachment to the existing wall. Think of it like a for-purpose frame member of a clear-span building, where the legs and overhead beam are assembled and stood... the weak point is where the legs attach to that beam. House projects are so fun... especially when there's old blown-in insulation in the way...
 ------------- Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest. |
Steve A wrote:Posted By: steve(ill)
Date Posted: 23 Apr 2023 at 12:34pm
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good reference and some charts.. https://alamcowood.com/downloads/Product%20Information/Glulam%20beam%20design%20tables.pdf" rel="nofollow - https://alamcowood.com/downloads/Product%20Information/Glulam%20beam%20design%20tables.pdf ------------- Like them all, but love the "B"s. |
Posted By: jaybmiller
Date Posted: 23 Apr 2023 at 4:07pm
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kind of fuzzy.... I don't understand the need for a beam. OK, remove interior wall...Usually NOT an issue ,as the trusses are supported elsewhere( outside walls ?) that wall would be a 'partition' and NOT load bearing structure. You should be able to simply 'scab' 2by wood where the top plate was and patch the drywall for the ceiling ?? ------------- 3 D-14s,A-C forklift, B-112 Kubota BX23S lil' TOOT( The Other Orange Tractor) Never burn your bridges, unless you can walk on water |
Posted By: Coke-in-MN
Date Posted: 24 Apr 2023 at 7:39pm
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On my lean to on back of shop I got several end wall trusses I used and applied metal roofing to purlins attached to the trusses . problem was when sag as end wall truss had simply vertical support not a V or slanted members in truss to spread load . On then I scabbed 2x10 on to each truss lower cord after jacking them up to remove sag . So learned some on truss design - and that was before i got my building inspection degree . ------------- Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something. "Challenges are what make life interesting; overcoming them is what makes life meaningful." |