Non-Loadbearing CFM walls as LFRS

[RFreund]

I've been seeing this more and more recently where the EOR is specifying that the non-loadbearing CFM wall system be used as a shearwall (either strapped or sheathed) to resist lateral loads.
In concept, I like the idea. There is a wall there, why not use it? However, when you get into the details, it gets hard to justify all the eccentricities involved. How do you put lateral loads into the wall and not gravity loads and resolve all the eccentricities? I'm posting this, hoping that someone comes to the defense of this system. I will try to defend it...
After posting this, I think I'm a believer. The eccentricities are resolved and for single story buildings of relatively short heights, I'd be ok with it. So this started as a rant/problem, but has turned into more of a PSA (too much effort not to post at this point). But I'm open to other ideas and input.

Problems common to both:
If you sheath or strap the outside (which is typically shown like that in the EOR drawing) you have to deal with the eccentricity across the wall thickness. This might be ok, because there is already eccentricity in these types of walls when you only sheath or strap one side. Many engineers forget this when designing strap walls, but you should account for this by applying a moment to your chord studs equal to wall thickness/2 * the strap force.

Situation-1 : No cantilever parapet.
In plane loads are resisted by a slotted connection to a heavy gauge track. Out of plane loads are handled by another slotted clip angle directly connected to the stud.

Situation-2 : Cantilever parapet.
This is a little tougher because you need to add a bunch of blocking. It is probably best to sheath this wall as opposed to using straps. In plane loads are resisted by a slotted connection to a heavy gauge blocking. If a strapped shear wall used, then you need to transfer compression through this blocking. Out of plane loads are handled by another slotted clip angle directly connected to the stud.

 

[KootK]

Some thoughts on your interesting PSA:

1) I concur with your original assessment and don't much like these setups. It always feels as though we're reaching a little too deep to try and please our clients which, of course, is good business.

2) When I review CFM connections for stuff like this, I find that the eccentricities associated with various forms of clip angle connections are conveniently forgotten / ignored. That, no doubt, because they are very difficult to evaluate and deal with.

3) I think that your analysis here is spot on and basically boils down to this:

a) It is pretty much impossible to allow slip connections in any of the parts of your shear wall system that would be considered to be the boundary elements for that shear wall system.

b) The detailing basically needs to be such that the shear wall is complete on its own with non-slipping boundary elements on all sides and the slip connections are separate from that.

 

[XR250]

I also dislike this approach. It takes relatively little red iron to equal the shear capacity of a LGS wall. Why not install some rod bracing or a diagonal instead of dozens of crappy little connections that will likely never be installed properly? The main reason I got out of LGS design was because EOR's are always trying to kick the can down the road.

 

[RFreund]

2) When I review CFM connections for stuff like this, I find that the eccentricities associated with various forms of clip angle connections are conveniently forgotten / ignored. That, no doubt, because they are very difficult to evaluate and deal with.

This is unfortunately true. I've spent a lot of time creating calculations for clip angles/screws to try and get a more reasonable assessment of their capacity.

The main reason I got out of LGS design was because EOR's are always trying to kick the can down the road.

Also, unfortunately true. I'm always surprised when I bring an issue up an there is severe push back. I think to myself, you didn't know or care enough to think this through originally, but now you're the expert?
You also bring up a great point about installation.

My other least favorite detail is when they want a brink lintel to be welded to hanging studs or a CFM box header.

 

[XR250]

My other least favorite detail is when they want a brink lintel to be welded to hanging studs or a CFM box header.

Yes, and also the 25 ft span headers....