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Re: Re[2]: Effective Length of Wall Studs

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At 04:34 PM 1/23/97 -0500, you wrote:
>I agree that the studs must be adequately braced against weak axis buckling 
>in order to have sufficient axial strength to resist even minimum specified 
>code live load on floors, snow load, and dead loads. And these loads do not 
>have to act together to easily exceed the allowable axial force based on
>axis buckling. In section A.11.3 of Appendix A of ANSI/NFoPA NDS-1991 
>"National Design Specification for Wood Construction", it states that in 
>light frame construction when stud walls are sheathed on at least one side, 
>the depth rather than thickness of the stud can be used in the l/d ratio, 
>with the proviso that "the sheathing be shown by experience to provide 
>lateral support and shall be adequately fastened." In most residential 
>construction I have seen, there is no bridging between stud walls.
>the exterior and interior sheathing is all that is available to brace the 
>studs in the weak direction. In the case of a house like mine with Celotex 
>and aluminum siding on the exterior, the 1/2 "gyp board interior is all that 
>is available as bracing. This construction is common, and I wonder what 
>testing has been done to demonstrate that the gyp board on one face of a
>adequately braces the stud to allow it to reach its calculated allowable
>capacity of 2100 lbs in the case of a S-P-F 2x4 Stud, as limited by strong 
>axis buckling. I am picturing a test setup with an 8 ft. long 2x4 stud, 
>toe-nailed into top and bottom 2x4 plates, with a 16" wide strip of 1/2" gyp 
>board (both long edges restrained to prevent in-plane lateral dispacement) 
>intermittently nailed to the 1 1/2" face of the stud over the 8 ft. length. 
>Its hard for me to believe that the axial load carrying capacity of this is 
>even the calculated **allowable** value of 2100 lbs, much less 2100 lbs 
>multiplied by a safety factor, which would be its implied calculated 
>capacity. Is there a gyp board industry group that has done any testing on 
>this ?
If you manage to justify the full compression parallel to grain of the
stud, don't forget that the compression perpendicular to grain of the top
and bottom plates will be exceeded.
Paul G. Adams, PE
Frederic R. Harris, Inc.
New York, NY
212 973-2951