Metal Stud Plywood Sheathed Shearwalls

[sgs114]

Hello,

I am working on a building that is to be framed with metal studs. The building is contains wide flange roof beams and metal decking. We are planning on using the exterior walls as shearwalls. These walls are non-load bearing and at some points the roof deck is approximately 35 feet above the floor slabe. I looked and I did not see any limitations as far as shearwall height goes with the exception of aspect ratio. As long as I am not violating aspect ratio requirements are there any other limitations to using metal stud shearwalls as a lateral system? The hold-down forces will be quite high, but we can manage those. We are in Seismic Design Category D and this is a risk category IV building. Thanks for your comments.

SGS

 

[KootK]

Neat. Any chance your boundary stud packs will wind up being HSS and thus be tricky to fasten the sheathing to? I suppose one could fasten the sheathing to a stud fastened to the side of the HSS.

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.

 

[sgs114]

Yes, I think we were planning on using HSS's for the boundary elements. I don't think we had gotten to the sheathing connection to the HSS yet, but your idea seems like a plausible one.

 

[XR250]

Never done one that high, but Kootk's ideas seems good if you choose to go that path. Are your studs really free-spanning 35 ft. or are there intermediate floors to brace it?
I am not a big fan of using metal studs for lateral stability of a structure of this height. Much safer to use red iron as the quality of metal stud construction is pretty poor and the detailing involved is pretty high. Then when they screw it up, you have to figure out a way to fix it and it ain't usually easy.

 

[KootK]

One thing that I've always found odd about sheathed shear walls is that, it seems to me, all of the studs will really see some axial load. I think that the studs nearest the ends of the wall will take the most load of course. But still, I see no reason why the second, third... fifth studs in wouldn't still take nearly as much compression load as the designated boundary member. In a wall 35' tall, I might start to wonder about the axial loads in those non-boundary member studs. I'd be concerned that you'd get a failure in the sheathing that would look a bit like shear buckling in steel plate. Essentially, a failure of the studs to properly stiffen the diaphragm panel.

This is just a thought that has occurred to me on occasion. I'm not sure that I'd even let it stop me from proceeding if this were a wall on one of my projects.

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.

 

[XR250]

I have had the same thoughts as well but could never quantify it.
This is one of my favorite things about metal studs design (not) - The EOR will delegate the design of a mess like this to me when it should most reliably handled with red iron IMHO.

 

[RWW0002]

Since you do not have the option for an R=3 system, make sure that all boundary elements and connections are designed for amplified seismic load (over-strength factor), or the maximum load the system can deliver per AISI. These are going to be some giant holdowns.

 

[SAIL3]

what type of sheating is being considered?

 

[sgs114]

We were planning on using 15/32" plywood. I am not familiar with red iron, that you guys have mentioned. Do you have a link of what you are referring to?

 

[KootK]

Red iron`s just another term for hot rolled steel. In this situation, it would probably require beams and columns inboard of your wall system.

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.

 

[jimstructures]

In the PEMB market red iron refers to anything painted/primed with red oxide structural primer including hot rolled and cold formed steel. In the last 15 years or so some manufacturers have switched to a grey water based primer for environmental reasons so maybe it will be called grey iron in the future. At the same time some of the same manufacturers switched to G30 galvanized secondaries, i.e. purlins and girts,etc. So I guess they are no longer red iron either.

Jim.

 

[sandman21]

DO NOT provide a slip track at the top of the shear wall, no product has been tested for in-plane shear and when tested they have performance issues. You are going to have slip tracks and some locations make sure that you have it clearly shown that above shear walls receives a normal track connection with screws or welds.

 

[mike20793]

sandman,

Great point about the deflection tracks; I didn't realize they performed so poorly for in plane shear. When you provide the normal track with a screwed/welded connection, do you design the studs to take some axial load as the steel beam deflects above deflects?

 

[sandman21]

Sadly I had one project which received a slip track, the retrofit was not pretty. Yes, for the load the studs will receive, the walls are typical installed after most of the dead load has been placed on the roof. That limits the amount of axial load on the wall.

 

[XR250]

Sadly I had one project which received a slip track, the retrofit was not pretty. Yes, for the load the studs will receive, the walls are typical installed after most of the dead load has been placed on the roof. That limits the amount of axial load on the wall.

Even more fodder for using structural steel for these applications. The metal stud installers will always come up with more creative ways to screw up your design. If nobody is paying attention, then you can have a big problem. To answer m20793's question, yes, you would need to design the studs as load bearing without a slip track.

 

[KootK]

Here, I took "non-load bearing" to mean an end bearing wall parallel to the roof framing that would see a modest axial load. Other than as a screw up, I don't see how a slip track could be used. The boundary fastening to the top track would interfere with the intended vertical slip, would it not?

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.

 

[sandman21]

We assumed that they would pay attention to the detail but since they saw slip at areas outside of the shear walls. We had a long talk about how they have done this on other project, etc.. I assumed that it was just talk but don't want someone to believe they can make it work, as fixing it was not fun.

 

[sgs114]

How do you figure an axial load to the wall as The beam above deflects? Do you assume all LL to the beam gets dumped into the wall below to be conservative?

 

[XR250]

yup

 

[sandman21]

Plus whatever dead load has not been installed. Walls typically go up after deck but before everything else.