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LVL verses plywood

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joe nelson

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I've been thinking about different types of woods for a project. I like plywood and have used it many times in building pretty much anything. While doing some napkin engineering, I thought of LVL. Does anyone have any experience in the use of LVL?
 

cgwendling

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LVLs are (laminated veneer lumber) the same as plywood, only they come in dementional lumber instead of sheet goods. Oh and one more thing, they should have an engineering stamp that can be plugged into a span table. They are primiraly used in load bearing spans to replace virgin lumber. Since large trees are rare and solid wood beams are cost prohibitive.

I use them extensively in building construction ,but have never seen them used in aircraft production. Also I've never seen them produced in anything smaller than six inches deep and 1" wide, (it doesn't mean that they don't exist) and once they are cut either for depth or width the span tables are no longer valid. One good thing is, you can order them, as long as you wish, but over 60' you need special transportation.
 

joe nelson

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CG,

Thanks for your post! I've read that LVL is stronger and lighter than conventional ply. Do you think it's a good substitute for ply?
 

Topaz

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Laminated spars, etc. are pretty common in wooden aircraft, but I would think you'd need to make a distinction: LVL is stronger than construction ply, but is the quality control and such up to aircraft standards? Aircraft plywood is a totally different animal than what you'd find in a building of any kind, where strength-to-weight isn't nearly as important an issue. I think a very careful look at the standards for LVL and aircraft-grade plywood is in order before you trust your life to something that might not be (and probably isn't) as trustworthy as aircraft-grade materials at the kind of stresses seen in aircraft construction.
 

BBerson

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Is the LVL plywood? Or is it a laminated beam like a 2x8 joist?
Does Home Depot sell it? Or is it available by order only?

Sorry for all the questions, if this is laminated lumber it might be worth a look.
 

Topaz

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If I'm understanding the guy right, it's that stuff you see in overhead beams sometimes: a laminated large-size piece of wood. They use this now instead of single solid beams because 1) architects have designed structures that need wood pieces larger (or in shapes other) than what's practical in single pieces and, 2) we've cut down all the really big high-quality trees.

I saw a TV special that included this stuff and it's pretty amazing. However, I still would question whether it's up to our quality control standards. The construction-grade stuff is allowed to have inclusions and knots to a certain degree, and I've never seen that allowed in any laminated aircraft structure such as a spar.

The other thing is that I think it'd be a tough go to find LVL lumber in pieces small enough for our use. I think most of them are rather sizeable, if I'm not mistaken.
 

BBerson

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You may be thinking of GlueLams instead of LVL. The LVL veneer is quite thin. A spar made of wood veneer could be superior to aircraft grade lumber in my opinion if properly glued even if it had some defects. It comes in normal lumber sizes and could be ripped to size.

Nearest dealer for me is 100 miles.
Specs and photo of LVL: http://www.gp.com/build/product.aspx?pid=1392
 

Topaz

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Huh. All those knots still give me the willies. Just a gut reaction. :ermm:

I'll take aircraft-grade stuff any time, just for the peace of mind. But then I guess I'm spoiled - Aircraft Spruce West is about ten miles away. "Shipping Costs" for me consist of how much gas it takes to drive the truck there and back...
 

alr

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Hi,

Coming a bit late to the discussion....

What about using re-sawn lvl lumber, e.g. making stringers and such from pieces cut out of lvl lumber? The lumber companies do not guarantee that resawn lvl meets full strength specifications, but what about strength-testing each resawn piece? Would 100% testing of each piece be an acceptable approach? Presumably, if the strength of each piece meets or exceeds, let us say, published strength numbers for sitka spruce then it seems reasonable (to me at least) that it would be safe.

Disclaimer: I am no expert... just seeking discussion and perspectives.
 

TFF

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Stringers or Longerons? Stringers are usually not structural, just form. First problem I see is this stuff is designed for something stationary with the occasional earthquake. Flying a plane is like an earthquake every few moments unless the air is glassy smooth. Figuring out how that equates will be hard. That’s going to involve glues and wood.

Gluelam with the right wood and glue would be perfect. But you have to know those and the quality control. LVL seems to be hardwoods and most airplane wood components are usually softwoods. Again quality control. Voids and knots allowed for a floor joist is completely unusable in a plane. It would be interesting.
 

Aerowerx

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.... Would 100% testing of each piece be an acceptable approach?...
Uh, no.

If you test each piece to 100% of capacity you would have nothing left to build with.

Now, testing a sample of each batch to 100% would give you some idea. It all comes down to statistics. Will you be confident enough in your samples to say that the entire batch is good?
 

Dana

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I think it's safe to say that LVL could, with appropriate quality control, be an excellent choice for aircraft construction, but the lower demands of commercial building construction means that the required quality control isn't there.

Once you start resawing it, all bets are off, especially as you get close to the veneer thickness. On a large beam with many laminations, a defect in one or two doesn't affect the whole all that much. But when there's only a few laminations, losing one could have a significant effect.
 

mcrae0104

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You will probably find that the strength-to-weight ratio does not compare favorably to Sitka or Doug Fir because 1) the species that the LVL is made up of may not have a great strength-to-weight ratio, and 2) there's a lot of glue weight in an LVL. Pick one up on a construction site sometime and see.
 

radfordc

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Uh, no.

If you test each piece to 100% of capacity you would have nothing left to build with.

Now, testing a sample of each batch to 100% would give you some idea. It all comes down to statistics. Will you be confident enough in your samples to say that the entire batch is good?
I think he meant testing to 100% of the specified strength requirement....not testing to destruction.
 
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alr

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Uh, no.

If you test each piece to 100% of capacity you would have nothing left to build with.

Now, testing a sample of each batch to 100% would give you some idea. It all comes down to statistics. Will you be confident enough in your samples to say that the entire batch is good?
When I say "100% tested" I don't mean tested to failure. I mean that all of the parts are tested to some specified value, such as the strength values of sitka spruce. Since most grades of LVL are stronger than sitka spruce the LVL would presumable pass without breaking, and if a given piece were to break it would be discarded. It seems to me that this testing scheme might be possible.

Your comment about statistics is well-taken. Of course, the same comment about statistics applies to solid lumber as well. One only has a degree of statistical confidence that a given piece of aircraft grade sitka spruce would meet spec if it were tested to failure. There is always a chance that it is a statistical outlier and will break under load. In the spirit of statistical reasoning, LVL lumber is generally more uniform in properties than solid lumber, and this should give greater confidence that an individual piece would pass muster, even if not individually tested, as long as the test results for similar pieces were good.

Regarding strength values, fb for coastal sitka spruce is listed as 1300 in the 2018 National Design Supplement by the American Wood Council (souce: https://awc.org/pdf/codes-standards/publications/nds/AWC-NDS2018-Supplement-ViewOnly-1805.pdf). Looking at some values for LVL, Westfraser lists fb for their lowest grade of LVL as 2750, a little more than twice as strong as coastal Sitka spruce. Their highest grade is listed as 3100 for fb (source: https://www.westfraser.com/sites/default/files/products/LVL/LVL Users Guide - Canada v0415.pdf) There are of course other strength values to consider as well. Also, other vendors will have different specifications for their LVL products.

With regard to weight, a year or so ago I picked up a couple of scraps of LVL from a construction site. I measured the density of the pieces and they came out to be 35.0 and 35.2 lb/ft3, which is heavier than Sitka spruce (typically 27 lb/ft3) and close to but a little heavier than douglas fir (typically about 32 lb/ft3). It is lighter than another aircraft wood, white ash (about 42 lb/ft3). I should say that I don't know what the strength specifications are for the two random pieces of LVL are that I picked up at the construction site because they weren't big enough to read the full stamp information on the boards, but the wood in the LVL I picked up looks like douglas fir.

Also, the laminations in the pieces I picked up are about 1/8" thick, so a piece cut to, say 3/4", will have 6 laminations. If one layer were bad it might decrease the strength by about 17% worst case (naive calculation, assuming the bad layer had 0 strength). Actually, it typically wouldn't be that bad.

One more thing, this with regard to weight. I just calculated the density of the 3100 fb listed by Westfraser and it came out to be 40 lb/ft3, which is a little heavier than the two pieces of LVL that I picked up. However, in terms of strength to weight ratio (3100/40=77.5) that is still quite a bit better than sitka spruce (roughly 1300/27=48)
 
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Aerowerx

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Why not just use aircraft grade plywood? It has well documented properties.

And, as mcrae0104 said, LVL will probably be heavy for the strength.
 

alr

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Why not just use aircraft grade plywood? It has well documented properties.

And, as mcrae0104 said, LVL will probably be heavy for the strength.
Please see my edited post of a few minutes ago. I added some info on strength/weight ratio.
 
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