Suspended load from bottom flange of CFS blocking

[P205]

This seems like a simple question but I can't find the answer or anything addressing it anywhere.

I would like to suspend a light load (less than 1 kN / 225 lbs) by through-bolting to the bottom flange of an 16ga or 14ga 12" deep CFS blocking. The blocking is in between floor joists that are 12" deep, 14ga.

My concern is that the load would tend to pry open the "C" shape.

Is this just not recommended at all?
If not, is there a better way to do this?

 

[KootK]

You might use a pair of 8" blocking pieces back to back-ish and run a bolt up between them with a washer plate on top of the flanges. You might check your original scheme by looking at the CFS blocking flange in bending using an assumed effective widtth.

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.

 

[BSVBD]

Do you have to use a bolt to support the suspended load?

Could you TEK screw a sufficient thickness of sheet or plate to the web of the blocking? Then fasten the bolt, if necessary, to the plate by welding or other method...

I would also prefer you sandwich the suspension plate between (2) C's as Koot similarly recommended, but, perhaps that's not necessary either.

I assume the end connections of the existing blocking are more than sufficient to support this load?

 

[dhengr]

P205:
Actually, screwing a plate to the back side of the “C” web (outside of the web) and bolting and hanging the load from that plate would be better, as suggested by BSVBD. This does several things: it gets the load up into web where you want it; it applies the load nearer the shear center of the “C”, thus reducing any twisting; and it gets the point load (bolt load) off the flange which is not thick enough to handle it, or distribute it into the flange and web without bending locally. A hanger btwn. two back to back channels would be a good solution too.

 

[dik]

dhengr: I would think the load located as far below the shear centre would be best.

dik

 

[Lomarandil]

Yes, if you can make the load path into the web work, below the shear center is ideal (since the load will self-stabilize a little against buckling). For most applications though, the effect is minor, less than 10%.

I agree that back-to-back is the cleanest and simplest option (maybe not cheapest)

----
The name is a long story -- just call me Lo.

 

[dik]

You might want to model it with CUFSM...

Dik

 

[P205]

Thank you for all the replies.

The floor joists are existing, but the blocking will be new, so I have the choice of blocking size, type, fastening, etc...

Back-to-back angle would work, but I feel it's a bit messier when connecting back to the main joists. Using a steel angle on the back side sounds pretty good. If things line up just right (they never do), I may be able to simply install the steel angle to the back of the floor joists instead of introducing blocking.

As for the TEK screw instead of bolt, I feel a bolt is more appropriate for a permanent load. No chance of pullout.

 

[XR250]

You could also simply run a 3 5/8"x14 ga stud flatwise between your joists and support the load from that. You could fasten it with light gage clip angle at each end.
Much easier to analyze as well although my gut says it is fine.

 

[P205]

I checked the bending of the blocking flange, as KootK suggested, and it appears that a 12ga flange, with the bolt load in the middle and assuming a width of twice the flange depth, can take a load of 1.36kN. I can space the blocking as such that the load is well below 1.36kN to take care of any unknown (like the bolt load being closer to the edge of the flange) and that should do it.