Notching Cantilevered Beams

[smokiibear]

NDS says that notching for a beam at the bearing point can be 1/4 depth per Figure 4A, NDS 2018. Does this same figure apply when cantilevering a beam, for example a house to deck, where the notch would occur on the top face where the deck steps down. When cantilevering from house to deck the simple span portion would have unnotched bearing. Is there different criteria to follow?

Thanks,

 

[KootK]

I think mid span, tension side notching rules would apply as the support is a location of high moment in a cantilever.

That said, people do this all the time in my market

 

[smokiibear]

Are you saying this is what you do all the time? Over 4" of notch?

 

[KootK]

I haven't done it personally but, yes, that is something quite common in my area.

It's a pretty serious no-no from a fracture mechanics perspective I think. Big old tension stress at a high moment location etc.

That said. I really do not see it failing catastrophically. I would expect that you'd just develop a crack from the notch up to the the top of the full depth section at a relatively shallow angle.

 

[phamENG]

Are you saying this is what you do all the time? Over 4" of notch?

View attachment 3275

Is that sawn lumber or an LVL?

Sawn lumber: you're nullifying the visual grading of the lumber by ripping it like that.

LVL: you're putting an LVL outside in a deck? That's a bad idea whether it's notched or not.

 

[XR250]

I usually sister it up with a 2x8 in this situation

 

[smokiibear]

I haven't done it personally but, yes, that is something quite common in my area.

It's a pretty serious no-no from a fracture mechanics perspective I think. Big old tension stress at a high moment location etc.

That said. I really do not see it failing catastrophically. I would expect that you'd just develop a crack from the notch up to the the top of the full depth section at a relatively shallow angle.

That's why I think NDS has the 1/6 Notch limitation.

 

[smokiibear]

Is that sawn lumber or an LVL?

Sawn lumber: you're nullifying the visual grading of the lumber by ripping it like that.

LVL: you're putting an LVL outside in a deck? That's a bad idea whether it's notched or not.

Unsure of what you mean, nullifying visual grading. Can you clarify?

It's a PSL with 3 layers of waterproofing at deck side.

 

[smokiibear]

I usually sister it up with a 2x8 in this situation

Yes...I would agree. Wasn't an option in this case. Needed 4 7x10.33x 18' long PSL's stitched together to take a point load. Client wants Trex on deck over living, so that's why the 11.875 depths are notched down to 7.75" and then sloped to 5.75".

I didn't want to do this, but what we did to account for notch requirements in NDS is put a horizontal cut at 7.75" for 24" back to keep stress cracking from occurring. Then, left the 11.875" depth joist in interior to flush with rest of the floor.

I just couldn't find any research on cantered notching for my situation.

If 1/6" notch works, and I simply add fur strips to the top of cantilevered joists to flush with the floor, what is the difference if I left the full depth of the 11.875? Does the stress fracture occur in the 11.875" because the neutral axis is higher than the depth required for 1/6 notch, (9.3"), which would then lower the neutral axis and push it further from the tension face at top of peak moment region?

 

[KootK]

That's why I think NDS has the 1/6 Notch limitation.

Yes, of course.

 

[phamENG]

Unsure of what you mean, nullifying visual grading. Can you clarify?

It's a PSL with 3 layers of waterproofing at deck side.

Well if it's a PSL, visual grading doesn't apply. But for sawn lumber, its grade (and, therefore, it's allowable stresses) are based on things like size of knots, location of knots relative the edge of the member, slope of grain, etc. If you rip a 2x12 down into a 2x4 and a 2x6, the grade stamp and, therefore, their permissible use under the IRC or IBC in jurisdictions that have adopted them goes away until the new pieces have been regraded. Same would apply if you rip it down to make that step.

As for the treated PSL...well...ask @XR250 why that's a bad idea.

 

[jerseyshore]

Ripping down a treated PSL is not allowed.

Unfortunately the client just isn't going to get a 6" deck at the perimeter if it's anything more than a juliet balcony. I would tell them they are going to have to live with 2x8's

 

[smokiibear]

Ripping down a treated PSL is not allowed.

Unfortunately the client just isn't going to get a 6" deck at the perimeter if it's anything more than a juliet balcony. I would tell them they are going to have to live with 2x8's

Were not ripping treated members. It's 3-layers of waterproof deck.

 

[jerseyshore]

Were not ripping treated members. It's 3-layers of waterproof deck.

I'm confused because above you say they are notching 11 7/8" members to 7 3/4" then sloping to 5 3/4".

Treated PSL's only come 3.5" & 5.25" widths and 9 1/4", 11 7/8", 14", & 16" depths. How are you getting from 11 7/8" to 5.75" without ripping them down?

 

[rb1957]

why not terminate the heavy beam at the support, and extend (sister?) with 2x6 pieces ?

what is the reason for the notch ? what is filling it ?? so narrow decking ??

I guess you're calling the overhang a cantilever ? I guess you're emphasizing the moment at the end of the notch ? which wouldn't be much ??
The heavy load is to the right of the support, no?

 

[smokiibear]

Because there is no room to sister with 4 7x11.875 beams stitched together to take the load at the end. Too much deflection at the end to put a large joist in there. So, either notch, or just fur up shorter joists, or use full size and put a horizontal cut at the deck notch to prevent some kind of fracturing at that point.