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?
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
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
RE: LVL Sagging
I would at a minimum stick a moisture meter in the LVL to see what you have.
RE: LVL Sagging
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
RE: LVL Sagging
RE: LVL Sagging
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
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
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
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
@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
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
EIT
www.HowToEngineer.com
RE: LVL Sagging
@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
RE: LVL Sagging
RE: LVL Sagging
RE: LVL Sagging
Brainless moment, clearly... Serves me right for posting while distracted by my two year old! lol...
RE: LVL Sagging
http://www.csgnetwork.com/emctablecalc.html
Pretty interesting
RE: LVL Sagging
RE: LVL Sagging
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
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
RE: LVL Sagging
"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
Thanks for the info.
FWIW, the sagging due to moisture story came from the manufacturers engineer as well in many cases.
RE: LVL Sagging
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
RE: LVL Sagging
RE: LVL Sagging
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
RE: LVL Sagging