Sagging Exterior PSL Deck Beam 1

[XR250]

I have a project where a 10-year-old exterior 3 1/2x16 PSL beam is sagging. The beam spans 18’-8” and supports 10 foot span floor joists. The beam is measured to be sagging 11/16”. I calculated it should be sagging no more than 5/16” supporting dead load only using a modulus of 1.4E6 per Weyerhauser and including a long-term creep factor of 2. I do not know who actually manufactured this beam, however. I probed the beam and it does not appear to be rotten. As such, I assume it is pressure treated,
About 15 other beams in this townhouse community are sagging similarly.
The sagging echoes what I have seen in other exterior treated engineered beams and have heard anecdotally from other contractors.

I don’t want to be the guy to condemn this beam and then have all the other townhouse owners calling me about theirs. How would y’all proceed? I’m leaning towards doing nothing.

 

[cec17]

How does it check out for strength? I've done some FRT and PT wood balcony stuff, from what I remember there are some hefty strength reductions (beyond the incising factor) for engineered lumber.

If it's fine strength-wise, you could chalk it up to creep and excessive deflection, set it up to be monitored periodically and do nothing for now. With a disclaimer that you can't account for continued deterioration. If its blown up, that answers it. It shouldn't too crazy difficult to replace.

 

[XR250]

D/C is about 50% so strength is fine.
"you could chalk it up to creep and excessive deflection"
How do you chalk it up to this? Why is the creep and deflection greater than calculated?

Thanks.

 

[Tomfh]

The fibers seem to be delaminating, which could indicate longitudinal shearing which may be contributing to the increased deflection. Weather damage might be a factor.


I’d exercise caution. Without conducting a proof test, I wouldn’t approve it.

 

[XR250]

Good call, Tomfh.
Probably cheaper to replace than test.

 

[ChorasDen]

Email their tech support, they may be able to help you further.

https://www.techsupport.weyerhaeuser.com/hc/en-us/categories/200165264-Contact-Tech-Support

 

[JAE]

I thought most PSL beams weren't supposed to be used in exterior conditions.

 

[atrizzy]

Agree with JAE.

 

[Tomfh]

Yeah, the glue is probably failing.

 

[XR250]

I thought most PSL beams weren't supposed to be used in exterior conditions.

Pressure treated PSL beams and columns are readily available. They have reduced design values though compared to non-treated ones.
I'll give Weyerhauser a call today and report back.

 

[PlinkoEng]

I would never use an EWP for exterior use unless it was fully sealed. The adhesives are vulnerable to temperature, moisture and UV. I've been trying to get Weyerhauser to tell me a safe temperature range for along time. Generally I will only install composites on interiors. Big exception is GLB but I have pretty detailed instructions for exterior use with flashing and sealing.

Here's Weyerhausers thing on moisture https://www.weyerhaeuser.com/woodproducts/document-library/document_library_detail/tb-112/

I don't necessarily know if the PT is actually meant for exterior service or if it's for higher risk service like a crawl space subject to flooding, direct installation on concrete or maybe to ward off pests.

Other weird material things I've found:

- GLB and LVL do much better than strand products in exposed uses.
- Don't let architects fly your glb beams past the roof/sealed deck line without serious capping. They break down over 5-10 years and become a rot path.
- PT is not a good exterior choice in dry environments or environments with big humidity/temp/sun exposure differences by season.
- Box frame pedestals around a column are a bad practice. It's not a matter of if it will destroy the column but when.

 

[XR250]

FWIW, Weyerhauser thinks this may be their beam. They are going to send a sales rep out to take a sample to test if it is treated. If so, they said they will replace it. '
Funny - apparently, they peruse this forum as when I called them they said were expecting to hear from me.
Unfortunately, my XR250 cover has now been blown
I have been really impressed with their help on this issue.

 

[PlinkoEng]

FWIW, Weyerhauser thinks this may be their beam. They are going to send a sales rep out to take a sample to test if it is treated. If so, they said they will replace it. '
Funny - apparently, they peruse this forum as when I called them they said were expecting to hear from me.
Unfortunately, my XR250 cover has now been blown
I have been really impressed with their help on this issue.

See if you can get a service temperature range from them! I've tried a few times over the years and never really got an answer.

 

[XR250]

See if you can get a service temperature range from them! I've tried a few times over the years and never really got an answer.

10-4

 

[TRAK.Structural]

I've always had good luck with Weyerhauser support. Report back with what you find out.

 

[XR250]

So I finally heard back from Weyerhauser. They sent a sales rep out there to take a sample. The beam is, in fact, pressure treated. They have chosen to do nothing about it however. Here is the gist of their response....

"Published creep deflection and member stiffness for wood products represent averages. It is reasonable to expect larger adjustments in higher moisture conditions and where wet-dry cycles can occur."

I don't even know what to say about this statement. This beam is located in central NC, not the PNW. We get an average amount of rain.

My take away from this is to design with an E of less than 0.5x10^6.

 

[TRAK.Structural]

Did they go as far as to give an opinion on the condition of the beam? Or are you still in the position of needing to address that with the client? If you are inclined to do something could you stiffen the beam, which would also strengthen it, to remove the unwanted sag instead of replacing.

 

[phamENG]

You should reply by quoting this back to them: Weyerhauser TB-101: Information about Creep

It essentially says "meh..don't worry about it"

 

[kissymoose]

No, if that is what they have to say, the take away is that no one should be specifying treated PSL products anymore. It's 10yo and falling apart, look at the picture.
Ludicrous response from Weyerhaeuser.

 

[XR250]

No, if that is what they have to say, the take away is that no one should be specifying treated PSL products anymore. It's 10yo and falling apart, look at the picture.
Ludicrous response from Weyerhaeuser.

For sure. I was being nice

Did they go as far as to give an opinion on the condition of the beam? Or are you still in the position of needing to address that with the client? If you are inclined to do something could you stiffen the beam, which would also strengthen it, to remove the unwanted sag instead of replacing.

They do not consider it an issue. I think the contractor may replace it regardless as it will hard to convince a future buyer this is OK.