Shearwall Penetrations every Stud Bay

[CBSE]

I have a school project where we are adding on to an existing school. We are adding enough square footage that I elected not to do any attachments to the existing structure and leave it alone. This week the architect sprung something on me in regards to wall separations. He has to provide a rated separation wall that involves using GP Shaftwall Systems. In order to make this system work, he has to removed the sheathing from the existing building and install breakaway clips to the existing studs.

My issue is that he is removing the entire lateral system on (2) really long walls (100 ft long walls). The total lateral force is only about 800 plf (ASD) along the length of the walls and there are only a couple of man doors.

My question (I have attached details for reference) is would it be problematic to have them punch 8" x 6" holes in my shearwall on the existing building at every stud bay to install these clips? In essence, I will lose about 1/2 of my shear transfer, but the loads are so light that it may not be an issue. I plan on blocking above and below the openings at every bay to help further mitigate issues.

 

[FoxSE14]

Looks like there is an issue with the link.

 

[CBSE]

Try this one?

 

[mike20793]

Is the shear wall sheathed on both sides or just one? That's kind of a lot of shear for just one side to be sheathed and just punch a bunch of holes in it without doing anything. If it weren't every stud, I'd say don't worry about it but it's every stud so I see two options:

1. Add blocking and straps to detail the force to transfer around the openings and keep (or close to) the original capacity.
2. Replace the gyp board with sheathing on the opposite side of the shear wall.

 

[FoxSE14]

I would prefer to keep the shear in the sheathing. Is it possible to add sheathing to the interior face (looks like you're already doing interior work to install the blkng).

I would add straps to call the line of blocking a continuous member.
See attached for my take.

 

[CBSE]

Thanks for the input. Removing sheathing off the inside isn't an option. We aren't doing any interior work. The contractor will have to toe-nail in the bocking.

Mike: Yes, the blocking and straps crossed my mind like a little force transfer situation. I think I will probably add in a combination of your comments in "1" and FoxSE14's.

FoxSE14: I like the idea of the sheathing on the inside face of the 2x blocking I will certainly add that in. That at least provides more continuity. They can just setup a line of blocking with sheathing, edge nail, and then cut the required block widths out...or at least that's how I would do it.

Thanks! I think I'm good to go.

 

[KootK]

My thoughts:

1) Is there really no way to clip the GP shaft wall to the studs nailing through the sheathing?

2) How will you attach the sheathing on the inside face of the 2x blocking if you can't remove interior sheathing?

3) None of the FTAO methods proposed seems to include the vertical chord/drag members required. Adding those would be tough.

4) In general I think that this takes the whole FTAO thing a bit too far.

5) I'd look at each remaining segment of sheathing between opening as a vierendeel truss web without the FTA boundary members. If it works based on in plane sheathing flexure and shear, great. If it doesn't work, back to the drawing board.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CBSE]

KootK: The exterior sheathing will be removed. So I was planning on blocking being installed from the exterior and having the contractor toe-nail the blocking to the studs. I will detail it so the blocking is a bit offset in the horizontal plane.

I would also require the contractor to build the little blocking panel prior to installation. So when they install the blocking, there will be sheathing on the back side of the blocking (as FoxSE14 suggested) and then edge nail the new sheathing to this blocking. I would then add coil strapping along the full length of each row of blocking. In wrapping my mind around this, it doesn't appear it would be much different than relying on blocking from a roof diaphragm to transfer loads to the double top plate. The only difference would be that the load is not taking a 90deg path down the wall, it is staying in the same plane.

I do however get what you are saying with the force transfer scenario. It would be a crap load of work the contractor.

I have researched the clips on the GP website, and there is not an alternative. I was hoping for some sort of square "C" shaped clip, but I couldn't find anything. It's an odd assembly.

 

[wannabeSE]

Help me out, I am trying to understand a few things.

1. How is the new roof supported? Since it is not attached to the new building, does the roof framing cantilever from a wall or beam not shown? I don't think the C-H shaft wall studs have much axial capacity. The heaviest that I have seen are 20 GA.

2. What is the purpose of the clips? If it is to reduce the shaft wall span, it would probably be easier and cheaper to use 4" or 6" studs if they can span from floor to roof without clips that penetrate the existing shear wall.

3. Can another style clip be used that attaches to the face of the existing wall rather removing the existing shear wall sheathing?

4. Are the shaft wall studs really 2"? I have only seen 2 1/2", 4" and 6" C-H studs.

5. Anyway this can work with the new studs at 24" OC? As far as I know, the shaft wall liner only comes in +/-24" width. So the contractor will have to cut 8" off each liner.

6. Has the architect worked out the head of wall detail where the shaft wall meets the (wood?) roof framing.

 

[KootK]

KootK: The exterior sheathing will be removed.

Ah yes. I now see that you mentioned that right at the top. If you could make a go of my vierendeel truss web concept, perhaps you could leave the existing sheathing in place. I won't pretend to fully understand the constraints at play here however.

In wrapping my mind around this, it doesn't appear it would be much different than relying on blocking from a roof diaphragm to transfer loads to the double top plate. The only difference would be that the load is not taking a 90deg path down the wall, it is staying in the same plane.

Interesting observation. Keep in mind that both roof diaphragm blocking and your system here require opposing vertical force transfer at the ends to balance out the rotation on the blocking panels.

I do however get what you are saying with the force transfer scenario. It would be a crap load of work the contractor.

I wonder if something like I've shown below might represent a modest improvement here. You have the same amount of shear wall but:

1) You get it in bigger continuous chunks which I like.

2) It seems less labourious.

3) The required FTAO boundary members occur more or less naturally.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CBSE]

KootK: I do like that idea. I dug through the separation wall documents, and it does appear that it is built for Steel Studs spaced @ 24" o.c. THANK YOU WANNABESE for catching that.

I have attached another idea. I can't remember where I read it, but it is in my memory bank that a shear wall cannot have more than an accumulation of 20% in holes in the length of the shear wall. Since I'm now restricted to studs @ 24" o.c., and I did a field verification of studs and blocking in the wall, I think this option might be the least intrusive and least expensive. The walls have blocking @ 24" o.c. surprisingly. I think if I specify 4" square holes, the contractor will still have room to get the screws in. I'm going to do a test on a piece of OSB at my house and see how difficult it is, but it seems really doable.

 

[CBSE]

For some reason it doesn't like my naming conventions, this attachment works.

 

[CBSE]

KootK: Also, I think your idea is easily justifiable. I will run the numbers on it later and see what it looks like.

 

[FoxSE14]

I like the latest ideas by you CBSE and also KootK's last thought. Trash mine, the OSB/blk assembly is going to be too awkward for the contractor to navigate into the wall panel if he's doing this along 100s of feet.