Wall Studs?

[abusementpark]

Ok guys,

If you are designing a wall stud as a beam-column and you have a two layers of wood sheathing on each side, is the stud braced for both compression and bending?

What about if you have wood sheathing on one side and gypsum on another? What about gypsum on both sides?

Intuitively, I think we can all see that these studs would not be completely unbraced and the sheathing would offer some resistance to buckling, but it might be hasty assume full bracing. Is there a legal document or code that quantifies this?

 

[DaveAtkins]

Bridging at 4'-0" oc should always be used with steel studs. Then if the sheathing deteriorates, the studs are still braced.

Remember, the studs will still be unbraced in the strong direction.

DaveAtkins

 

[csd72]

and the bending is in the strong direction so the sheathing doesnt help that.

For gypsum I would only take the studs as braced at each bridging.

 

[ash060]

I typically assume that gypsum or plywood will brace the compression flange of your steel studs for bending only. I include the bridging for the torsional restraint and weak axis for compression. I still do a striaght steel design, not a sheathing Braced design, (unless plywood on both sides) for the axial loading.

So for axial load KyL and KtL would be 4'0" c/c or the spacing of the bridging, and the full L for Kx.

For Bending it would be continuously braced. So you could use FySe for the allowable moment.

If you dont count on the sheathing to brace the compression flange for bending you will have trouble getting studs to work for typical wall heights.

 

[dougantholz]

If gypsum can be used to resist lateral loads, to me it can be used to brace a stud for compression and bending. I don't usually use the stud compositely with the sheathing but I understand there are several research reports that indicate this is an acceptable practice.

 

[ssweetland]

Refer to AISI "Standard for Cold formed Steel Framing - Wall Stud Design" Section C3.2. Basically, there is an option to design with sheathing braced conditions, including Gypsum. For axial design, minor axis can be assumed to be braced at 2 X screw spacing. To prevent screw connection failure you must limit the Maximum member Axial load according to Table C3.2-1, (basically 5.8k for 1/2" gyp and #6 screw, etc, etc). For Bending design, you can assume compression flange is brace, hence Nominal Mn = Se X Fy.

 

[abusementpark]

Ok, sorry for the confusion here.

I was referring to WOOD studs.

 

[msquared48]

I would assume the studs as braced in the weak direction for both ply and gyp on both sides of the wall. I would not assume fully braced if only have ply or gyp on one side of the wall, which can happen. Here, I would look to any fire blocking as providing a lateral restraint point. As previously stated, bending in the strong axis would not be affected by the ply or gyp.

Mike McCann
MMC Engineering

 

[DaveAtkins]

My bad! I design with steel studs a lot, so I just assumed...

But I have designed with wood studs a lot as well, and I basically agree with Mike. However, I seem to remember something (maybe in a previous Code) about wood studs being braced even if sheathed on just one side. I know my garage doesn't have sheathing on the inside...

DaveAtkins

 

[DonPhillips]

I agree with Mike on being conservative if a wood stud is only sheathed on one side. If it may buckle, adding blocking should reduce its effective length enough to avoid full sheathing on the interior.


Don Phillips

http://worthingtonengineering.com

 

[abusementpark]

Thanks for all the responses and generally agree with your intuition. I am just wondering if there is any reputable study or governing document that acknowledges these situations and gives you direction on what assumptions to make.

 

[msquared48]

Professional Experience?

Mike McCann
MMC Engineering

 

[DonPhillips]

You can use Breyer's and NDS to determine when the stud will buckely if only sheathed on one side. I am not sure it is worth the calculation unless your are looking at a large building.


Don Phillips

http://worthingtonengineering.com