Light gauge exterior wall overhang

[jturley]

I've come across a question from contractors a couple times which I don't have a clear answer for. Many time a light gauge exterior wall will slightly overhang past the edge of an elevated slab. Usually its an inch or so, so no big deal. I've had the question raised about what the maximum overhang is. I know that using PAF's has edge distance minimums and that controls for fastening into concrete. However just pertaining to the wall its self assuming a normal one story wall what would be the limiting factor for overhang. Would you look at the cross sectional area of the stud and the amount of bearing they have? I'm sure there's got to be some kind of local crippling or some thing. For instance I have a particular location where I am fastening a LG wall to structural steel so the PAF edge distance isnt a problem but there are only leaving me like 2 inches of bearing. Not sure how to check that other than engineering judgment.

 

[XR250]

What demand and what gage studs and track? You also end up with an outward force at the top of the wall due to the eccentricity. it usually ain't much, but still should be added to any other demand at that connection.

 

[CANPRO]

If the stud wall is being installed to the underside of an elevated slab, or in your specific case, structural steel, is the stud wall load bearing (gravity) or just there for wind? It sounds like your studs are wind only (some dead load from cladding), so the bearing stress on the overlapping portion of the studs should be very minimal anyway. Can you clarify the nature of loading on the specific wall in question?

 

[MotorCity]

If its a load bearing wall, I'd be inclined to check local bending of the track that overhangs the slab based on the axial force in the studs. Otherwise, if it just resists out of plane loads, I might allow 25% to 30% as a reasonable amount. The edge distance of your track fasteners to the slab may control also.

 

[jturley]

The question was meant to be more general in nature but the specific case I have on my plate currently is an infill wall for gravity only. I was thinking along the lines of MotorCity but the studs and the track work together as fastened so checking the track for bending about the axis parallel to the track is kinda weird. The stud fastening into the two flanges of the track would stiffen the track against bending but I have no clue how much. Maybe you could treat it like a point load applied to the end of the stud at the flange. You would have like a non-linear region until the load distributed into the full cross section. I'm thinking like D region B region in concrete. Seems like it would need some empirical data. Cant think of any relevant sections in the AISI. What does everyone use conventionally as a personal maximum overhang they allow?

 

[KootK]

I believe that you rarely have your studs in full contact with the web of the track. 1/8" gap or something like that. Either by way of fasteners or hangup on the track radii, I think that you're almost always flange supporting your stud work. You'd think that would have some kind of consequences for local crippling in the studs but, to my knowledge, that's not a thing that gets checked. As far as the cantilever goes, the fact that the studs never actually touch down makes checking the track in bending appealing. Of course, then you're back to having to eyeball an effective width unless somebody know of specific guidance that applies. And, by virtual of relative stiffness, it probably means that most of your load ends up being transferred through the interior stud flange.

I recently reviewed a submittal where studs were supporting 0.6" form deck above with no track and the deck flutes running perpendicular to the stud webs. I asked about local buckling as it seemed to me that all the load would be delivered to just a couple of spots on the studs where there was actual contact. They thought I was nuts and I'm quite sure that they still do. It's interesting how specialists in a field eventually stop thinking about that field's idiosyncrasies. It just morphs into accepted dogma.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.