Wood Flitch Beam - Notched Bearing?

[DigiAlmond]

Hey all!

I'm working on a higher end residential home, and the goal from the architect is to "use as much wood as we possibly can". I'm all on board with that. Now I'm running into an issue where a wood "girder" is supporting a beam that is approximately 10" above said girder. Both beams are approximately 16" deep. Now one solution would obviously be to move the girder down so that the beam can bear directly. This would work but it has some issues I'm trying to skirt around, but notching the beam would be such an easy solution... That got me thinking: a notched beam bearing is usually pretty big no. Notching a beam effectively reduces the depth of the beam by however deep the notch is. However in a flitch beam, couldn't the bolts start to engage that "lost" depth? I'll probably still try to find a better solution, but what do you guys think? Am I missing something?

Thanks!

 

[ChorasDen]

Depends on how you're designing the flitch beam. Is the beam sized in such a way that the steel portion can support all of the design loading, and the wood is used only as the visual piece on the outside, and/or to provide some nominal buckling resistance, or is the assembly designed where some of the wood itself is required to support the load?

 

[driftLimiter]

Can you provide a sketch of what the condition looks like? Notched beams bearings can be done just need to be carefully detailed.

 

[KootK]

1) The notches can be reinforced with GRK screws and the like. That said, if there's a way, I'd certainly seek to avoid the notches.

2) The notching is really worse than just a reduction in the available shear depth of the cross section. It's more of a fracture mechanics issue where the notch becomes an unpleasant stress concentration. For this reason, if you're still using the wood structurally, I think that the only way to avoid dealing with the notch at all in the flitch beam scenario is to arrange your connectors in such a way that all of the shear in the wood pieces gets transferred to the steel plate ahead of the notch. This could be a bit awkward in that the normal way to detail flitch beams for shrinkage is sort of the reverse: the shear in the steel often gets transferred back into the wood prior to being transferred to the support.

3) If your project budget could support a flitch plate, perhaps it could instead support some custom fabricated steel connection hardware that would allow you to, effectively, deal with the notch within the hardware.

What prevents you from raising the low beam up in this situation?

 

[TidePoolJunkie]

I would definitely check KootK's option 1. For shear design, you lose capacity due to the reduced depth, then a Cvr factor of 0.72, and then a (dn/d)^2 (reduced depth over gross depth)^2.

If you're shear doesn't work with the notch and you're willing to rely on non-North American design standards, there are lots of guidance (MTC Solutions, Eurocode, NZ code) out there for reinforcing notches with self-tapping timber screws (GRK, Assy, Rothoblaas, Schmidt, Simpson SDCF screws).