Another Wood Moment Connection Question... 5

[XR250]

The Architect wants a 3 ft. awning over a large portion of this house. Rather than get into using exposed diagonal rods, I suggested we use a system as shown...

Was going to attach with 10d nails but could also use bolts or screws. The loads seem reasonable and the majority of the time it will only have dead load.

I appreciate some feedback.

Thanks!

 

[jayrod12]

I don't see an issue here in that regard.

What would concern me is the building envelope details at the joint. I've had to repair way too many wood awnings/canopies where more attention was paid to how it looked than how well it shed water.

 

[Celt83]

you can create a connection that can handle moment but you can rarely create a moment connection in wood.

Your 30 psf seems light does that include drift from the roof above?



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[DaveAtkins]

Agree with jayrod12. Structurally, it looks OK.

DaveAtkins

 

[phamENG]

This is exterior, I'm assuming? I think it's going to sag over time. It'll be installed, the wood will dry out some, and then wind variations will cause an irregular cyclical movement over time that will ever so slightly "wiggle" the nails in the connection. Add to that creep inat the nails, and I don't think you have a connection that will last the life of the rest of the structure. If there's any leak at all in the flashing then it'll really be toast.

I don't think bolts will be any better as the holes will necessarily be larger than the bolts to put them in.

If this is the only way, I'd say use a high strength, creep resistant construction adhesive with the nails, and make sure the nails are ring shank or some other withdraw resistant fastener.

 

[KootK]

If it works by the numbers, especially wind in a low snow region, that's good enough for me. How does it drain? I like to tilt things like this upward a bit so that they don't look shabby when they start to creep downward. But, then, maybe you don't want the water running that way.

 

[Celt83]

This looks like a decent paper on the topic: Link

and another: Link

My Personal Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

Open Source Structural GitHub Group:

https://github.com/open-struct-engineer

 

[XR250]

@Jayrod - Noted

@Celt83 - The roof above is flat and protrudes the same amount

@phamENG. - I like the idea of using construction adhesive. Seems like that would mitigate short-term cyclical movement - which should help preserve the connection.

Thanks!

 

[XR250]

If it works by the numbers, especially wind in a low snow region, that's good enough for me. How does it drain? I like to tilt things like this upward a bit so that they don't look shabby when they start to creep downward. But, then, maybe you don't want the water running that way

It is a low snow area. I imagine we will tilt it downwards 1/4"/ft. That way it will drain and look intentional when it does sag

 

[KootK]

I also like the adhesive idea.

 

[EngineeringEric]

If you want a pair of suspenders, feel free to throw a Simpson A35/A34 clip on the top and bottom of this after you glue and nail it. It'll give a bigger moment arm and likely give you a FS=4 when taken with all the systems you have

 

[kipfoot]

I'd take your moment arm back to the centroid of the fastener group.

I think that taking the couple from the top and bottom row will give you a conservative fastener load, so that's fine. You'll get some contribution from all fasteners based on the distance from the centroid of the group.

 

[XR250]

@EE - Good idea

@Kipfoot - Good point

-Thanks

 

[kwinner]

I would think about using SDS screws to reduce number of fasteners (avoid splitting) and add some compression between the members.

 

[jayrod12]

Less fasteners isn't always ideal in wood moment connections. More likely to allow unreasonable slip in the connection. More fasteners (provided you can meet all the minimum spacing/edge distance requirements) would result in a much more rigid type connection with minimal slipping.

 

[dik]

Careful for end distances and by fixing the material at the edges, the wood can split by shrinkage strains...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[JoshPlumSE]

I don't like it. Too many failed wood balconies in recent years. You get people partying up there and jumping around. Combine that with Wood's poor behavior in cross grain bending and tendency to damage over time (dry rot, moisture issues).

If it were me I would have a strong preference for one of the following:
1) An extended back span that could take the moment instead of trying to transfer it to a post.
2) A kicker brace (up or down to stabilize it).
3) A hanger from above at the cantilever tip. Maybe to a steel beam with a backspan above.

I'm not saying that it can't be done. I'm just saying that I'm not personally comfortable with that detail. There's no redundancy and we're relying on an effect that's been problematic in the past.

 

[jittles]

I'm not saying that it can't be done. I'm just saying that I'm not personally comfortable with that detail. There's no redundancy and we're relying on an effect that's been problematic in the past.

I agree with Josh, even if this isn't a balcony condition here.

It's not something you will find on my drawings.

 

[HouseBoy]

The bending moment doesn't seem too large but I would wonder about the flexibility of the 2x6.

 

[Agent666]

Last time I did something like this I used a glulam/laminated member and laminated the central ply right into the column, so it turned up as one piece. No fasteners needed. They were also doing glued/laminated portals on the job, so adding this in was easy. Architect had an aversion to using any visible fasteners on the entire job (came up real sweet though).

Had to design joint using fracture mechanics as it's glued, apart from getting my head around that it was fairly painless.

EDIT - photo of said detail

https://engineervsheep.com