CFS Stud Bracing Confusion

[StrEng007]

I found a CFSEI Technical Note that discusses bracing for light gauge studs. One particular section seems to go against the consensus that I've read here.
The generally accepted idea being that, providing sheathing on wall studs would cut down the unbraced length for axial loads.

This is disputed by the note that brings up a topic I haven't seen discussed here before:

https://cfsei.memberclicks.net/assets/docs/technotes/tn-559.pdf

"if the load-bearing wall also serves as a shear wall, the sheathing should not be relied upon to provide bracing for members under axial load."

With that being said, I'm sure that a majority of exterior load bearing walls also serve as shear walls. Also, no matter what direction the MWFRS wind is blowing, you're always going to have either windward, leeward, or side wall pressures. So should we really be designing walls studs as being COMPLETELY UNBRACED for both gravity and lateral loads? How can an exterior load bearing wall ever really be subjected to ONLY bending or axial?

 

[KootK]

Yikes. One would think that similar logic would also apply to wood studs.

And it's not as though the non-shear walls in a building actually respect that classification. Stud walls, like me, are notoriously bad listeners.

I suspect we'll have to ignore this unless it surfaces as a hard code requirement that can be enforced.

 

[phamENG]

I typically call for discreet bracing of metal studs simply because they're so spindly. With wood studs, you can usually get away with letting them go unbraced during construction. Not so with a lot of metal studs, and so requiring that bracing gives the contractor more flexibility with phasing the sheathing attachment.

Regarding damage at design lateral loads - I suspect this is more a concern with steel studs. When we're talking about gypsum joined to a 0.0625" thick piece of steel with a screw, there's a lot that can happen locally to degrade the connection. A nail shot through plywood into a wood stud? Not so bad. And even if it is damaged, my 'gut' tells me there's a bit more residual capacity in the damaged connection in a wood assembly than in a steel stud with a screw that disengaged or a stud flange that yielded.

I had not heard of that concern, though.

 

[StrEng007]

Putting that CFSEI note aside, is it fair to say you agree that bridging as shown below will cut the weak axis compression buckling by half when located at mid wall. It will also do nothing to improve the unbraced length for flexure?

So KL/ry is reduced by 50%, while Lu for flexure remains at the full stud length?




... and then if you're inclined to use the sheathing for something, let it help with Lu?

 

[Celt83]

Bridging by itself no, bridging with either end jamb studs or end diagonal/K bracing designed to transfer the force from the bridging into the diaphragm yes.

 

[StrEng007]

End jamb stud meaning you take the collection of 2% loads and push the summation into the end stud for weak axis bending?

 

[KootK]

Regarding damage at design lateral loads - I suspect this is more a concern with steel studs.

I would like to see some testing on that as my instinct is the reverse.

Based on what I've seen of steel deck seismic testing, I would expect to see some screw plowing through the CFM but no pullout and no outright separation of the fasteners from the studs.

With wood studs, I fear the situation shown below.

If we are to have this shear wall limitation, I would hope that it would eventually take the form of "sheathing may brace studs so long as drift < XXX".

 

[EngDM]

Bridging by itself no, bridging with either end jamb studs or end diagonal/K bracing designed to transfer the force from the bridging into the diaphragm yes.

I'm curious as why Bailey provides load tables for axially loaded studs and specifies the capacities are applicable to walls braced at 4' on center, but doesn't say anything about restraining the bridging at the ends.