Deflection of stud walls at ends (where wind pressure is higher)

[alhawk]

At my firm we calculate the out of plane deflection for stud walls. The deflection is limited so that the stucco will not crack. Because of the increased wind pressure at the ends of walls, when we get above 9' tall walls we almost always use 12" spacing or tighter for the first 5' of the wall to limit deflection. (The interior studs are typically 16" spacing.)

I understand why the wind pressure at the end of a wall is higher than at the interior. However, it seems that when we are calculating the deflection in a stud, the studs near the end of the wall should benefit from the return wall at the corner. I think that even though the wind pressure is higher at the end, the defection of the stud a mid-height will decrease as the studs get closer to the corner.

Do we need to worry about the stud spacing at the ends of walls?

We are based in Utah and the majority of our work is for homes in Utah and Salt Lake Counties.

 

[msquared48]

I would think that would only apply to the first one or two studs where any exterior plywood or interior sheetrock could add the the bending resistance. More than a couple of feet away, I would do what you are currently doing...

Mike McCann
MMC Engineering

 

[jittles]

I agree with Mike.

Remember to take your .7 reduction factor on C&C pressures for the purposes of deflection calculations (if you are using the IBC).

 

[structSU10]

You can also account for the wind area per stud as the stud length, L times no greater than L/3 according to the commentary of ASCE 7. This, along with the 0.7 coefficient helps a lot too.

 

[a2mfk]

Also remember how cheap studs are, at least the standard 8' variety was $3 yesterday @ a home improvement store in Florida...

But I think your increased stiffness at corners thinking may be from CMU and tilt panels, where I know many engineers use returns in the walls to help brace the edge zones in those types of assemblies.

 

[alhawk]

Thank you all for your input.

structSU10 do you have a section or page for your reference to L/3 in the ASCE 7 commentary?

 

[structSU10]

First page of commentary for wind (Section C6), under the section for component and cladding a few paragraphs in it reads "The secon case arises where component such as roofing panels, wall studs, or roof trusses are spaced closely together;...".

 

[UcfSE]

alhawk, That's in the definitions in the ASCE 7, main code. 7-10, p243. 7-05, p22.

 

[Jerehmy]

if it's ASCE 7-10 wind loads, you take 0.42 reduction instead of 0.7 for deflection.

 

[DST148]

@Jerehmy: ASCE 7-10 wind loads are given at strength level. It basically amounts to the same thing as ASCE 7 - 05,
i.e. 0.7 / 1.6 ~ 0.42.

 

[Jerehmy]

@DST148 - I know but it doesn't mean he knows the IBC factor goes to 0.42, which is why I made the comment lol.

 

[alhawk]

We are definitely using all the applicable reduction factors. We use the final factor ends up being 0.7*0.6=0.42.
Really I was just hoping we could benefit from the return walls.

Thanks for your thoughts
-Alex

 

[TDIengineer]

The return wall is braced by the top track of the perpendicular wall. The top track of the studs you are checking can span some distance which will act as a support for those end studs. What about using a boxed track at the top of parapet for the first 8' or so? What is your a dim? You could provide double or triple studs set back from your a dim, and span the built up top track to the jamb you created.

Just a thought.