Wood Connection Help

[TRAK.Structural]

Hi All,

Need help figuring out the best way to connect a wood beam to a wood post. See attached. This is at the corner of a structure where beams spanning opposite directions meet over a column. Currently the beam spanning in and out of the page is shown through bolted to a notched section of the column at the top. The beam spanning left/right on the page is where I am having issues. Both beams are part of knee braced frames so there are some loads to resolve but I don't have any good ideas at the moment of what makes the most sense in terms of general connection scheme here.

Any and all suggestions are appreciated.

 

[phamENG]

It's bearing, so I'd go with toe nails and a strap for whatever uplift comes from the brace load.

 

[dik]

Can you notch the post for the beam to bear on. Use a single bolt near the bottom... two bolts with moisture change may cause the beam to split... pham's idea of a strap is good for any uplift.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Eng16080]

I don't think I would notch the post at all. Rather, cut it flush and set both beams on top with the beams butted together at a 45 degree miter. For the uplift, use one strap centered on the outside face of the post for each beam. Nevermind, didn't read the detail correctly. Assumed both beams are flush, which they're not.

If you use thru bolting, I definitely agree with dik concerning the moisture change issue. With the bolts oriented in the perpendicular to grain direction of the beam, they will want to move with the beam as it shrinks/expands perpendicular to grain (especially as it dries out initially). Meanwhile, with the same bolts oriented parallel to grain in the post, they will generally not move in the post since parallel to grain dimensional change in wood is negligible. This difference in movement between the beam and post could result in one or both members eventually splitting. As dik says, one bolt near the bottom would be better. The NDS code, Section 12.5.1.3 limits the max. distance between fasteners perp. to grain to 5" for this reason.

 

[phamENG]

The orthogonal beam is sitting on top. Mitering won't do anything. For wood-to-wood connection like this I don't usually worry about differential shrink/swell. Between the slop that is typical in these connections and the fact that the post will move with moisture too (though obviously not nearly as much), I've never known these to be an issue. A metal connector or anchoring to another material with vastly different properties, absolutely.

If anyone does have experience with these wood to wood connections over restraining one another and causing splitting, please share. But for the sake of stability and restraining the beam from rotation at bearing you'll need a bolt up high.

 

[TRAK.Structural]

Pham - I like your idea about the strap

Dik - The beam is already bearing on the post so I'm not sure what you mean about notching it further.

Eng16080 - Straps will work for uplift, but I also have some amount of axial load in the beams that transfers to the posts. That's the main reason I have notched the post and through bolted the first beam. I am using small diameter bolts (1/2") and keeping the spacing perp to the grain for the outermost bolt rows to 5" for the reason you noted about shrinkage.

Wood Works has a connection design tool that I am using and its surprisingly difficult to get the connections to work even with small magnitude loads.

 

[XR250]

Very hard to get this to work with orthogonal knee-braces happening at the corner (I assume this is what you were talking about). Can you move one of the knee-braces to the next bay?

 

[ChorasDen]

What's the LFRS here? Is there a shear wall running into/out of page that is not shown in the detail? How are you getting lateral loads from the roof diaphragm into the beam, and then out of the beam into the foundation below?

 

[dik]

It's already notched, then... the comments about the number and location of bolts is good.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Eng16080]

The orthogonal beam is sitting on top. Mitering won't do anything.

Yup, I missed that. Should have looked at the detail a little closer. Forget the idea about the miter then. Makes no sense.

For wood-to-wood connection like this I don't usually worry about differential shrink/swell. Between the slop that is typical in these connections and the fact that the post will move with moisture too (though obviously not nearly as much), I've never known these to be an issue.

I can't say that I've personally observed this being an issue either, although the thru bolted connection shown by OP is generally not recommended by lots of wood connection design literature that I've come across as well as the NDS code (assuming the 5" overall spacing is exceeded here). My own judgement call is to try to avoid this type of connection, in lieu of something more along the lines of dik's suggestion.

Straps will work for uplift, but I also have some amount of axial load in the beams that transfers to the posts. That's the main reason I have notched the post and through bolted the first beam.

Perhaps I misunderstand your lateral system, but with a knee brace, shouldn't the axial force be resisted by the knee brace with there being minimal axial force transferred from the beam to the column?

Wood Works has a connection design tool that I am using and its surprisingly difficult to get the connections to work even with small magnitude loads.

Wood connections in general can often be a struggle. I don't think this is specifically an issue with Woodworks software. Without knowing the specific loads you're dealing with it's difficult to comment further.

 

[phamENG]

I can't say that I've personally observed this being an issue either, although the thru bolted connection shown by OP is generally not recommended by lots of wood connection design literature that I've come across as well as the NDS code (assuming the 5" overall spacing is exceeded here). My own judgement call is to try to avoid this type of connection, in lieu of something more along the lines of dik's suggestion.

It's also precisely how it is 'detailed' in prescriptive codes for decks and porches. As long as we're dealing with reasonably sized wood here (built up sawn lumber or perhaps a timber up to 12 or 14" in depth), I wouldn't be concerned.

I've seen the cautions not to restrain shrink/swell in these sorts of connections, too...but I've never seen that caution with respect to wood to wood connections. It's always involving steel saddles or straps or knife plates or other metal components that will decidedly not move with moisture changes. What in the NDS are you referring to specifically?

 

[TRAK.Structural]

XR250 - Unfortunately I don't have much opportunity to shift braces around.

Choras - Blocking and perimeter beams with transfer the diaphragm loads to the LFRS, which is knee braced frames (all sawn lumber members)

Eng - See attached snips from my model, one shows axial loads and the other shows shears. Shear in the top of the post as well as axial force in the beams at the post/beam intersections indicate a shear transfer is happening there. I am using compression only braces as a measure of conservatism, not sure how that affects the frame behavior in this regard.

Pham - Posts are 8x8 and beams are 4x12 so generally I feel comfortable with the sections I have.

I'm not an expert on wood connections (obviously) but for similar loads a handful of through bolts would have to be replaced by 12-20 wood screws, I would have concerns with splitting/damage to the wood members in that scenario as well.

 

[Eng16080]

What in the NDS are you referring to specifically?

I'm referring to NDS 2018, Section 12.5.1.3:

In terms of various prescriptive requirements for this type of notched connection, most guidelines that I've come across seem to respect this 5" maximum distance. For example, here is a deck post to beam detail from AWC DCA6: "Prescriptive Residential Wood Deck Construction Guide." You'll notice that the max. perp to grain distance is <=5".

 

[phamENG]

Got it. I thought you were saying there was something that said you couldn't have bolts on both sides of the neutral axis or something in line with the glulam connection guide and other popular documents.

We're in agreement. Like I said - reasonably sized lumber. 12" or less and you meet the 5" rule easy, larger lumber takes a bit more thought but still isn't hard.

 

[ChorasDen]

Someone out there help me out. I've never liked knee braces in wood, and never use them. How do you develop a capacity for the assembly, and what kinds of loads are you resisting with the brace?

 

[jayrod12]

For true knee braces, I only consider them active in compression and have both the post and beam notched to allow direct bearing transfer of the forces from the brace to each element.

 

[Eng16080]

If all else fails, I think a connection like this may work, with a steel angle wrapped around the outside corner:

 

[SE2607]

I really like screws (like Simpson SDS screws) in lieu of bolts for wood connections. They don't have the spacing problem of bolts (avoids the > 1/4" issue) and doesn't have the slop of bolt holes.

Wood connections in general can often be a struggle.

I officially nominate this as the understatement of the year!

 

[Aesur]

Disclaimer: I didn't read all the responses, however why not use a Simpson CC or CCQ type attachment, or even make one? If the beams are at different elevations, make a custom steel bracket with wood filler beneath the upper beam.

 

[SE2607]

Aesur - Those buckets are pretty expensive, especially a custom fabricated one. A standard CC for ECC is over $100.