CFS Fasten Joist Thru Gyp Bd to Stud 2

[RPMG]

Are there special considerations when fastening through gyp bd? I would say that it is not permitted because it places screws in flexure.

 

[BridgeSmith]

Yes, the fasteners are in bending, which would have to be accounted for in the design of the fasteners. There would also be increased displacement at the connection, and potentially increased flexibility of the connection due to the low crushing strength of the gyp board.

 

[Ceinostuv]

Have a read through the attached document from Structure magazine(and CFSEI), it should provide a neat answer to your question. OSHPD also has a document out there where they did their own testing and came up with similar reductions for different gaps. Hope that helps!

Judgement-In-Training

 

[RPMG]

It seems to me that a 5/8" long metal spacer/sleeve/bushing would reduce the tendency for the screw to tilt.

I looked into toggle bolts, and they seem to have low load ratings. This is probably because they're tested on gyp bd only attachment. They would also place a 1/2" diameter hole in the stud.

Does anyone have a recommendation for specific fasteners?

 

[BridgeSmith]

The small toggle bolts I've seen are typically flimsy pieces of junk, which wouldn't hold much regardless of how strong the substrate was.

I don't know much about what fasteners would be available or suitable for your situation. The sleeve idea could probably work with a bolt that was strong enough, but what is the problem with just cutting the gyp board out so you can attach the joist directly to the column (stud?)?

For this attachment to a stud wall, what I've seen done (and what I've done myself) is to attach ledger (rim joist?) to the ends of the joists, cut out the gyp board for the ledger, and attach the ledger to the studs. That way, I don't have to try to line up the joists with the studs, and I have redundancy in the support system.

 

[Ceinostuv]

RPMG, out of curiosity, do you find issue with the factors explained in the article I had attached?



Judgement-In-Training

 

[Ron]

Reducing the tendency to tilt with a bushing only concentrates the bending at its worst point. Reduction as suggested by LaBoube seems reasonable.

 

[RPMG]

HotRod, add a ledger and repair gyp bd for fire-rating. That's what I was looking for. Thanks.

Ceinostuv, the tests were done on 43 mil CFS with 1/4" screws, but the recommendation is to use a reduction factor of 0.74 for 33 mil or thicker with any diameter screw. I think that's a serious red flag. The paper makes very strong conclusions that are simple to understand, but it requires a lot of faith in the authors.