Sagging Exterior PSL Deck Beam

[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.