New deck joists sistered to existing cantilevered joists?

Question

New deck joists sistered to existing cantilevered joists?

shacked (Structural)

(OP)

18 Oct 19 19:23

I am working on a project, 2 story residence with an existing 8 to 10 foot cantilevered deck. All wood framed construction in Southern California. The existing floor & deck consists of 2x10 DF joists that sit directly on top of 11-7/8" TJI joists. The first span is 18ft, which is the interior house floor & then they both cantilever from 8 to 10ft as an exterior deck. Please refer to the attached pdf that shown the existing and proposed condition.

If I sister new deck joists spanning the full new deck length to the existing 2x10 upper deck joists and remove the lower TJI joist at the deck I have some concerns about the actual loading to the new beam supporting the deck and wall above.(noted on attached pdf). Note that there is also a new wood framed shear wall approximately 16 inches behind the new dropped beam, so not the existing 2x10 will be a multi span condition.

The reaction for this condition is what you would expect with a larger gravity reaction on the wall and an uplift over the beam.

The more I think about this solution the more I think that there may be another better/cleaner solution.

What are your guys thoughts, opinions?

Thanks

https://files.engineering.com/getfile.aspx?folder=b118d7db-2b50-4d28-9bb1-5

jayrod12 (Structural) · Answer 1 · 2019-10-21 14:47:55

I'm not sure why you are removing the existing TJI, could you elaborate?

Also, can the existing 2x10 joists support the shearwall load at the location noted? I feel like 2x10 spanning 18ft are pushing the limits at the best of times, throw in a point load and you're asking for trouble.

shacked (Structural) · Answer 2 · 2019-10-24 03:22:49

No, the TJI's are remaining below the existing 2x10's at the 18ft span, but after the new dropped beam where the deck begins they will be removed. Then I will add new LSL deck joists from the new dropped beam to the front of the deck. I had planned on sistering(wrong term) the new LSL joists to the existing 2x10 so that the 2x10's can remain in place in order to protect the existing deck surface. As I started thinking about the 2x10 now being supported at 3 places, the back of the garage, the new shear wall and the new dropped beam, in addition to the sttachment to the new LSL's I begin second guessing the reactions and how the deck will perform.

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New deck joists sistered to existing cantilevered joists?