Wood Stud Framing - Sheathing & Blocking to achieve stud bracing 1

[StrEng007]

I have arrived at some confusion regarding the role that sheathing and blocking play when it comes to bracing the studs used in wood wall framing.

Below is a list of statements that provide my current understanding of how we apply these materials. Please don't get upset if something I have written is wrong, I'm trying to get things straight and provide a reference for anyone else who searches this topic in the future.

If anyone has codified references, whether from a building code or design standard, that supports my answer or whatever the correct answer is, please let us know below.
If any statement for #1 through #7 is incorrect, please let us know.

Sheathing provided to brace wood studs for axial loading (not flexure/out-of-plane loading)
1) Sheathing must be applied on ONE SIDE only. This will only brace the stud against axial buckling about the stud's weak axis.
2) Gypsum board sheathing is unreliable due to vulnerability to damage. Therefore gypsum board sheathing doesn't provide any axial bracing.
3) If the sheathing also acts as the sheathing panel for a shear wall, you cannot use this sheathing to brace the stud for any axial buckling.

Sheathing provided to brace the wood stud length for flexure/ out-of-plane loading
4) Sheathing must be applied on BOTH SIDES since wind occurs in two directions.
5) Gypsum board sheathing is unreliable due to vulnerability to damage. Therefore gypsum board sheathing doesn't provide flexural bracing.
6) If the sheathing also acts as the sheathing panel for a shear wall, you cannot use this sheathing to brace the stud for flexure.

Blocking provided to brace wood studs for flexural loading, axial loading, and combined bending and axial.
7) Full depth blocking provided at mid-height of stud, reduces the weak axis slenderness ratio by 1/2 AND reduces the flexural unbraced length by 1/2.
8) The blocking from statement #7 must be continuous across the entire wall segment.

Two follow up questions:
Q1: If there is no sheathing at all, and only blocking is provided, how do you handle the build up of brace forces that exist in the blocking?
Q2: If there is sheathing applied, and the sheathing is attached to the blocking, can you disregard the build up of shear forces and accept they are simply handled by the sheathing through vertical diaphragm action? Or do you need a discrete method to resolving that load (similar to the design of cold formed steel stud)?

 

[SWComposites]

3) If the sheathing also acts as the sheathing panel for a shear wall, you cannot use this sheathing to brace the stud for any axial buckling.

Why not?

Sheathing provided to brace the wood stud length for flexure/ out-of-plane loading

flexure in which direction? strong or weak axis of the stud?

 

[phamENG]

2) I disagree. Gypsum is certainly capable of bracing studs. Granted, I call for blocking in interior bearing walls just in case, but that's more to ensure they don't get too carried away during construction and over load the wall before it gets sheathed.

3) Never heard of that one before. The bulk of the lateral shear is being taken by the edge nailing. The field nailing will still brace the studs. If you wanted to really break it down, yes, the small brace force vector required to brace the stud would be combined with the force vector from the lateral load resistance, but it's not going to be enough to change the design values of the shear wall or stop it from bracing the stud.

4) No. It can't brace it out of plane. The stud is stiffer than the sheathing in that direction. You could use adhesives and screws to create a composite section, maybe, but it's not going to brace the strong axis. There's no way to do that without adding a buttress.

5) See 2.

6) See 3.

8) add to that "and has a load path to the foundation." Usually just getting back to a diaphragm is more than sufficient as the design lateral loads are way higher. In wood, the sheathing typically handles that.

 

[Celt83]

1) yep, See NDS section A.11.3
2) nope gyp board is commonly considered for bracing, if it can be used for global shear resistance of the building it can handle the bracing forces.
3) not aware of any language to this effect
4) Nope, sheathing need only be applied to the compression face of the member in bending to provide bracing for calculation of CL or Lateral Torsional Buckling. If you have load combinations that flip the compression face then yes sheathed both faces.
5) nope gyp is commonly considered for bracing
6) not aware of any language to this effect

7) Only if there is a complete load path to ground for the blocking forces
8) ..... and have a continuous load path to ground (this is a commonly missed detailing element of cold-formed stud walls).

Q1: You need to design a full load path for the brace forces to ground, either king studs to receive the blocking and span vertically or diagonal members in the wall plane to kick the force down to the diaphragm. Generally once its in the diaphragm its usually hand waived from this point to ground as the bracing forces should be orders of magnitude lower that the applied lateral loads.

Q2: I gather most would say the sheathing takes over the bracing duties, but can see a pretty solid argument for the self weight loading to be baked into the bracing.

 

[SE2607]

FYI, there is usually fire blocking at mid-height of the wall, but that might be just at 1 hour (i.e., exterior) walls.

 

[ANE91]

Don’t let any crotchety engineers (me included) deter you from posting questions and getting answers that everyone can benefit from. Nothing else to add; @Celt83 ‘s answers covers it.