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LVL Sagging

LVL Sagging

LVL Sagging

(OP)
Have any of you observed LVL's sagging significantly more than calculations would predict.
I am seeing a case of this every few months. About half are in crawlspace but with what seems to be normal moisture levels.
Many times, the deflection is three times of what the calculations predicted.
Anytime I have contacted a manufacturer about their product, they send a field rep out.
They conclude the LVL's were installed wet and the deflection happened very quickly.
I am not buying it in all cases. The beams seem to have a wax coating to prevent moisture absorption.
I believe there is a widespread problem with the testing or manufacturing of the beams.
Fortunately, I have had only one case on a beam that I designed and it was two sizes larger than code minimum.
The contractor ended up sistering it with steel channels.

Thoughts?

RE: LVL Sagging

There was a very common problem with steam processed Glulam around here (Ottawa, Ontario, Canada) in the 1980s... The members would deflect excessively and the glue joints would eventually separate if left unaddressed. Maybe the glulam industry in your area has tried to accelerate their cure process through steam?

Or, alternatively, someone isn't keeping the LVLs dry... Installed with elevated humidity (to say wet is a bit much) is very likely to be your issue regardless of who's at fault.

RE: LVL Sagging

If that's true, and the deflection is 3x what you calculated, then that means the modulus of elasticity is reduced by 67%? I'm not buying that as a result of slightly moist conditions.

RE: LVL Sagging

Also, if you are talking about a house , design floor live loads are usually WAY more than the actual/normal live loads being applied. If you have witnessed large deflection in the built condition, I think you have a real problem, as most likely when you inspected it there was only a small percentage of the design live (and dead) load being actually applied.

I would at a minimum stick a moisture meter in the LVL to see what you have.

RE: LVL Sagging

(OP)
Calculations were based on estimates of actual loads, not design loads.
I have not stuck a meter in any of them, but many were inside houses so they could not have elevated levels except during construction.

RE: LVL Sagging

Are they all from the same manufacturer?

RE: LVL Sagging

(OP)
Seems to vary. I recall Truss Joist, Weyerhauser, Willamette

RE: LVL Sagging

I've understood there to be a drying of the wood elements of LVL as a very early step in the LVL manufacturing process. Then the fibers are oriented and then glued(generally with exterior glue, I think interior glue is hardly used anymore, if at all, by the big fabricators)and then assembled and pressed and cut as required.

I think it would take a significant amount of time to introduce enough moisture to infiltrate into a finished LVL to induce a deflection under load much different than it would off of the assembly line. In other words, I don't think that LVL getting wet on an uncovered truck ride to the jobsite, or getting a few days rain before installation on a jobsite, would be enough. It takes a long time for wood to dry and I think it takes a long time for wood to "undry".

RE: LVL Sagging

What region are your jobsites in?

My engineered wood guru tells me some folks have been bringing in some low grade off brand stuff. The names you mentioned are all major brands though....
Sometimes, of course, contractors buy the cheapest they can from a yard and ass u me that they are all equivalent.

RE: LVL Sagging

(OP)
North Carolina.
They seemed to all be name brand.

RE: LVL Sagging


Just curious, were the suspect beams stamped with the grade and modulus of elasticity?

RE: LVL Sagging

I am not a wood guru, but could it be related to poor quality timber, ie if they have been using SYP but not at the 2012 reduiced values (reduced by some 30%) then that could explain a good sag under 'normal' conditions. I would also be curious as to the type of crawl space, (conditioned, vented, or semi). If vented and in a humid environment (James Hardie has a good table for Zone 5 or 10 in humid conditions) then their easily could be condensate forming on the plywood, running down joists and to the LVL girders... I know it seems like a stretch but not uncommon in the south.

The other thing relating to if they were too wet when installed would just be if the sag is new or old. if it was old then all the settlement would have happened in first year, have been repaired and then a dip would have been left with no new signs... if it deflects later then it wasn't from bad construction.

You can always load test one :)

RE: LVL Sagging

(OP)
@Triangled - They were all 1.9 or 2.0E. Do not recall the grade
@Eric - Crawlspaces were all vented and did not seem to have a moisture problem. I'll leave the load testing to the manufacturers :>
I think on the next one, I will push the manufacturer to send out one of their actual "Engineers" and let them observe it first hand - rather than just their normal rep.

RE: LVL Sagging

1. Hard for me to believe the wet installation story as I noted above
2. I could believe a contractor installed wrong materials - as LVL and LSL and rimboard and timberstrand are called by some people all the same thing, and E can vary from 2.1 to 1.3 to 0.6 for rimboard. BUT you observed grade stamps on your boards.
3. Could believe that bogus, ie miss-stamped, materials have been installed as my engineered wood guru said some off brand materials have made their way into some yards. BUT you're think they are major brands.
4. LVL has been performing well for years now and I've never heard this problem. I'd triple check my calcs, and then, absolutely get their licensed guy to the field.

RE: LVL Sagging

I wonder if they were overloaded at some point and now have permanent deformation? I have heard contractors 'believe' that LVL's are more susceptible to creep over time, but I cannot attest to this. Seems odd...

EIT
www.HowToEngineer.com

RE: LVL Sagging

(OP)
@Triangled - The LVL's appeared to be genuine.
@RFreund - I agree with the contractors that they seem to creep.
In all cases when I contacted the manufacturer I was given the same story -"if you put them in wet, they will creep alot until they dry"
Anyhow, I guess the moral of the story is to not go anywhere near code minimum deflection design - seems to hold true for all modern wood products.
Don't get me started on creeping floor trusses!

RE: LVL Sagging

I think you are all significantly underestimating the effect of moisture on LVL. Some manufacturers go so far as to stipulate that their products can only be used in environments under 15% humidity... That's really quite dry!

RE: LVL Sagging

Under 15% humidity...... isn't that unrealistic in a real world application?

RE: LVL Sagging

(OP)
Do they not mean 15% moisture content? - not the same as humidity

RE: LVL Sagging

SteelPE & ExcelEngineering... Yes, of course, Moisture Content (of the LVL), *NOT* humidity! My apologies.

Brainless moment, clearly... Serves me right for posting while distracted by my two year old! lol...

RE: LVL Sagging

Article in Structure mag April 2012
Engineered Wood Products Exposed to Floodwaters.

"Elevated moisture contents can also affect the stiffness and creep performance of wood members. Creep is an increase in deflection that occurs over time under sustained load or exposure to moisture; this increase is typically only applied to dead load deflection because the live load applied is considered too transient to produce creep. Raising the moisture content from dry in-service conditions to fiber saturation decreases stiffness up to 25%, thereby causing an additional deflection of about one-third more than calculated."

RE: LVL Sagging

regarding LVL from Russia from my guru.....

Imported LVL from Russia; it comes into USA in North Carolina and is distributed up-down the East Coast. It’s values are 25%-30% lower than equivalent LVL from USA & CANADA. Many folks have made the mistake of using it expecting it to perform like DF or SYP LVL; it doesn’t. I also don’t know if it has any sealer on it to limit moisture absorption.

See ICC-ES attached
See Advisory attached

Good luck!

RE: LVL Sagging

from APA-EWS.
"To the best of my knowledge all LVL producers' technical literature and APA Product Reports limit the use of LVL to dry service conditions where the average moisture content of sawn lumber is less than 16 percent. However, that is not to say that LVL cannot withstand incidental moisture exposure due to reasonable construction delays or other conditions of similar severity. E.g. the following is copied from the Moisture Effects section of APA Form E705: Proper Storage and Handling of Engineered Wood Products (attached), "When engineered wood products are exposed to normal jobsite wetting and then dried to long-term moisture conditions the structural properties are not compromised. It's important, however, to minimize excessive moisture exposure with proper handling and construction techniques." "

the attachment has their chart (page 5) relating relative humidity varying from 10% to 90% to a corresponding LVL moisture content varying from 1.2% to 19.4%. The dry service condition limit of <16% mentioned above occurs when relative humidity is somewhat over 80%, and, I would suppose, for some length of time.

The OP indicated 3x calculated deflection. I still don't buy the sales rep story of moisture.

RE: LVL Sagging

(OP)
@Triangled
Thanks for the info.
FWIW, the sagging due to moisture story came from the manufacturers engineer as well in many cases.

RE: LVL Sagging

Excel,

This isn't a one time incident is it? If this has happened multiple times I don't know if I would buy the moisture argument either. Something isn't right with what is going on here. Is this happening with the same mfr or different mfr's?

RE: LVL Sagging

(OP)
Multiple occurences over the years, different manufacturers

RE: LVL Sagging

I'd take your calcs, plus field measurements, plus sales reps licensed engineer's comment that 300% deflection is not surprising when "wet", whatever he means by "wet", plus Struct mag article indicating "up to" 1/3 more deflection maximum when saturated, to APA-EWS and request support. It's their mission to support the Engineered Wood industry. It's not making sense.

RE: LVL Sagging

Quote (ExcelEngineering)

This converter gives an estimate of wood moisture content versus humidity

http://www.csgnetwork.com/emctablecalc.html

Pretty interesting


Quote (wannabeSE)

The Forest Products Laboratory has a publication that includes equilibrium moisture content for place around the world (mostly US cities) http://www.fpl.fs.fed.us/documnts/fplrn/fplrn268.p...


Find this odd as I don't see moisture content higher than 30%. We have used moisture meters in wood on a multitude of inspections into attics that weren't properly ventilated and found 40%+ MC. I think our moisture meter may be faulty lol

RE: LVL Sagging

Jerehmy - or a leaky roof!

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