Bearing Strength - CFS Framing

[phamENG]

I have a somewhat unique condition (thanks, framing contractor!) and I'm realizing that AISI doesn't have a bearing check - am I right or just missing something?

I specified some bypass deflection clips to connect the offset wall to a steel beam. Rather than do that, the framer made their own "clips" out of track. They actually work (barely) in tension, but in compression they have to bear on the flange of the beam. They cut the flanges of the track so it could sit on top of the top track and have the 'lip' of the web slip under the beam and fasten to the flange. So I have .00825in² of bearing area at each track flange.

I'm assuming there's a combined local stability/yielding combination to be considered. Just not entirely sure.

This is mostly academic at this point - I'll be giving them a corrective detail. But I'm curious if anyone has more insight. Thanks.

 

[dik]

Do you have a photo? and what sort of load are they taking?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

dik - sorry. My pen tablet is on the fritz and I got fed up with it. Drew this one with my mouse since I knew it would be necessary.

Taking about 300lbs (ASD) at each attachment.

 

[XR250]

I think I would have to see a photograph to be helpful

 

[driftLimiter]

Are those track flanges up tight to the beam bottom flange? Could be curious how the bearing area at that interface compares to the bearing area of the screws.

AISI can get us the critical stress for those flanges that you could compare. Because of the way the shear will flow out of the flanges and down to the web I would think its more of a shear problem and then a local compression.

 

[phamENG]

drift - yes, they're tight to the beam flange (in most cases, anyway). If anything the bearing area is probably better than screws, but my gut tells me it won't behave the same way since it's out on a free edge.

 

[driftLimiter]

Its on a free edge yea, but the stress at the extreme fiber (top) of the flange diminishes to zero pretty quickly. Its a case of non uniform compression on an element that is stiffened on one edge only. Also a case of shear lag.

I might be thinking of aluminum but I thought AISI had some (fairly) simple equations to get the allowable stress on a leg like that when I get some time I will check.

 

[dik]

Horizontal, I assume?... looks like a 300lb connection... if vertical, then it needs work...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Celt83]

gross

the one in your photo already looks like it has a tear along the track web.

I wouldn't think there is any bearing between the track lips and the steel beam bottom flange, at least not until a fastener failure or web buckling failure occurs. Your not likely to find any direct guidance from AISI on this one you'd probably need to kick to and FEM approach or maybe rationalize some form of stiffened distortional buckling check for the track lips loaded in compression from the anticipated bearing.

 

[phamENG]

Celt - that's precisely what went through my mind when I saw it. The tear in that one is from an overly aggressive attack with a pair of shears. A few of them are actually better, but still not good enough for my taste.

I was thinking of FEM, too, but I'm not going down that road. Of course the alignment of the top track makes any sort of deflection or bypass clip impossible now...it'll have to be a clip angle and a brace angled down slightly to the face of the stud..

 

[Celt83]

you might be able to get something like a Verticlip SLF in there: Link

 

[dik]

Is that a tear or a cut? and what caused it? 300lbs seems too small to do that sort of damage. Is the CFS wall loaded from that assembly?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

Celt - good suggestion, but it doesn't quite fit. They'd be trimming something with those shears again.

dik - it's a cut. It happened when they were cutting the flanges off to make it fit against the beam flange. The orientation is as shown in my sketch. Rather than tie the top of wall assembly to the beam using a bypass deflection clip and appropriately placed bridging with torsional restraint, they put a top track on at the same elevation as the bottom flange and 'strapped' it back with this little custom "fabricated" piece. So that clip is loaded in tension or compression (shear in the screws/PAFs) when the wind blows on the wall.

As for the CFS wall being loaded from that assembly, I'm guessing you're asking about the beam? No. The 'custom clips' are too widely spaced and lack the flexural rigidity to transfer any gravity load from the beam into the wall.

 

[dik]

clips just to brace the top of the wall, so they can be loaded in tension or compression, but no vertical load.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[phamENG]

dik - correct, that is what they are used for.

 

[Aesur]

If what they have there works for tension, I would maybe just add a steel angle/bent plate attached to the bottom of the beam and bearing against the track at some spacing for compression and call it a day. I doubt you would get 300 lbs bearing on what's left. Maybe something like an SCS or SCB could work with shot pins to the beam, but installed opposite of normal, such that the slotted holes are aligned to the beam and the bent leg is against the top track.

 

[phamENG]

Aesur - solid suggestion, but as always there are constraints. I'm doing an angle with pins to the bottom flange of the beam and a small stud (a 1.62S works well enough, and they should have some left over) to the face of the stud for the compression. It's a renovation, and the soffit and eave are existing and not in the budget to rip out and replace.

 

[structSU10]

Is there wall above? If there is I would clip the stud above to the beam and let it cantilever down and connection the bottom track to the studs above.

Why is this not a vertical slide clip? Its probably flexible enough to act as one but that steel above must move vertically due to loading right?

You could also run a stud on the other side of the steel beam and extend it down, double clip it to the steel, and vertical slide clip to the verticals of the wall.

 

[phamENG]

Why isn't it a slide clip, you ask? Well..."Deflection clips are typically used with metal stud walls, not 2x4 wood studs." No joke. That's the reason the contractor's PM gave for why his framer ignored my specified connector and made up his own thing.

I already have the solution - that was never really an issue - I was just curious about some of the finer points of CFS analysis and how that sort of condition would be analyzed (preferably using AISI hand calcs and not FEM). Because on paper it seemed like it could almost sort of work. And, for whatever reason, it's always these little jobs where this stuff happens and then somebody hires another engineer to say it works and they present some half baked analysis that, indeed, says use this many screws and this many PAFs and the track has this capacity and 'in my engineering judgement...' *hand wave with jazz fingers* it works! I take a sort of sick pleasure (my business model is not great, by the way) in turning around and providing a more advanced analysis showing that person's engineering judgement is FUBAR.