Stud Shear Wall for Steel Frame 1

[RG88]

FYI...I have posted this on the Moment Frame and Shear Wall Forum, but decided to post it in this forum as well to maximize possible responses.

I am working on a single story conventionally framed steel building. The roof system will be standard barjoist framing supported on wide flange beams. Due to some architectual limits on the placement of internal columns (which subsequently limits 'K' bracing placement) and the client's desire to keep the framing & connections simple as possible, I have run into an issue that I haven't really seen before. Has anyone ever used steel stud framing (curtain walls) as a shear wall for structural steel framing? I have not seen this before and the architect is asking that I do my homework on why it cannot be done before he reworks the interior framing to place the braced frame where I feel it should go.

I have worked on similiar structures with exterior masonry shear walls and other 'stud skinned' steel framed structures with braced frames, but this project cannot have braced frames in the exterior walls. The next location for an internal braced frame parallel to this exterior wall is pushing the limit for using the roof diaphragm to transmit the shear back to the interior braced frame. In other 'stud skinned' steel framed buildings, I have been able to use the roof diaphragm to transmit the shear to an internal frame and resrict the drift of the exterior wall within allowable limits.

I am aware of the moment resisting frame option, but I would prefer to use that as a last resort because of the difficulty in obtaining easily constructed connections between HSS columns and wide flange beam sections. Also the dead load on this particular exterior wall is very small so uplift becomes another issue with moment resisting frames. It might help to understand my dilemma by knowing that this is design build and the client is a steel erector with their own thoughts; however, they cannot find any past projects that disagree with my position...that it is not an acceptable or documented practice to use steel stud curtain walls to brace a steel frame structure. The studs are not infill so they are on the outside of the steel framing. The exterior columns are of course inset from the studs so K bracing on the exterior will eat up valuable space and will send the architect into a fit. I have also worked with CFSM on residential projects and am versed in developing shear panels with those members, but this idea of using the steel stud framing as a shear wall for the frame just doesn't sit well with me. I am open to any references or ideas that others may have.

 

[DaveAtkins]

You can certainly use a non-load bearing steel stud wall as a shear wall. Section 2211 of the IBC covers this. You can use OSB for the sheathing, but most often GWB is used. Since the wall is non-load bearing, you will probably need holddowns each end of the wall to resist overturning. Check the Simpson website -- I think it is the HTT that can be fastened to a steel stud with screws. To get the load into the shear wall, I use the slide clips -- they are attached to the steel beam or rake angle, and to each stud. I have never seen values published for the sideways capacity of a slide clip, but generally each clip takes a small load, which can be justified by inspection.

DaveAtkins

 

[CSEllc]

I'm using the similat system on a project right now. The difference is my roof is framed with light gage metal roof trusses.

I am using plywood (or OSB) for the walls.

 

[Indianola]

It's a perfectly fine method. As mentioned above, IBC covers gyp, plywood/osb, and gauge metal steel panels. Be sure to read the text. The table is full nominal strength before factor of safety reduction. The seismic R value for such systems limits you to 4 stories.

There is also a listed (ER report)product, which is gypboard bonded to gauge metal steel sheets. It is installed like gyp, but gives the higher steel values.

If higher values are needed, in the cold-formed section of the code, metal diaphragms are allowed by calculation (Section D). The commentary for the cold-formed section refers you to the Steel Deck Institute for calculation method.

There are also some ER reports for metal deck screwed to steel suppports that could be used.

My recomendation is to avoid using strap x-bracing. This is sometimes seen in low seismic areas. It performs poorly under dynamic load. - it is hard to get tight and it can't be pre-tensioned. The lateral load will freeling move the building until the slack is taken up. The sudden load hammers the bracing, further streching it. The ATC-20 field guild has a great after-earthquake picture, that is very effective in convincing clients not to use the system. There is such a seismic penalty place on the system, that seismic will control regardless of what seismic zone you are in. It often gets built in low seismic areas simply because they don't think to check seismic, because it doesn't control for anything else on the building.

I have tested a number of light gauge steel stud shear assemblies. They have excellent ductility. Very similar load curves to plywood on wood stud.

ALLWAYS double-stud at the ends of shear walls. They are prone to end-stud buckling & track end uplift. If you don't take care of those details, you won't get your anticipated strength.

While simpson lists values for their HTT (called S/HTT when used with steel), a better holddown is their PHD series. Throw away the wood screws and use #14 (1/4&quot tek-screws. The values are allowed to be calcuated. (look for the equation in the cold-formed chapter. in the UBC'97 it's section 2218.) This gives higher values than the HTT, is easier to install, and has less in-service deflection.

Needless to say, I've done a number of these, several have been through a 7.0 quake and come through unscathed.

 

[RG88]

Dave,

I agree with your thinking 100%. That is how I originally approached this problem. When I couldn't find an example in my overwhelmingly vast collection of books and reference materials I began to have some concern. Thus is why I posted the thread to seek the input of others. I have seen alot of different ways to frame steel, but using a stud wall to brace a structural steel frame caught me off guard. I have used light gage straps to brace steel studs with light gage steel roof trusses but not a structural steel frame. Do you have any thoughts on using light gage diagonal straps in-lie of OSB and securing the straps to an L bracket? The L bracket would be anchored to the foundation with J-bolts and the bracket would fit inside the bottom track. The upper portion of the diagonal would be secured to a double stud that is in turn clippled to a rake angle and wideflange steel perimeter beam. I would probably use L sections in-lieu of clips at the double stud...this way I can develop a stonger connection at that point.

 

[RG88]

Indianola,

It appears that you have posted while I was replying to earlier posts. Your thoughts on diagonal bracing are well taken. I am in low seismic (North Carolina). Wind dictates for most of the state with one & two story strucures. I like the plywood idea...I use it on timber framing all of the time. The trick for me is to get the client to agree to plywood. As I mentioned in the response to Dave, I am curious as to what others have done when they have to brace a structural steel frame when standard rolled section K braces are out of the question and moment resisting frames are the last resort. Thanks to everyone for their replies thus far!

 

[Indianola]

If you go the the strap bracing option, be sure to check seismic. Because of the extremely low R value for the system, and the additional requirement that tension-only bracing has to be designed with the Omega multiplier, you will find that seismic will often control for the strap bracing even in North Carolina. (With a building aspect ratio of 4:1, it will control over a 110 mph wind load in seismic catagory A.)

 

[unclesyd]

Here are a couple of links that have some very good information on steel framing.

http://www.ssma.com/technical_library.htm

http://www.dietrichindustries.com/