shear value for screw into drywall? 2

[Lion06]

Does anyone know where I can find an allowable value for shear (bearing) for a screw into drywall only?
I have an existing condition that I need to put a number to, but can't find any information.

 

[structuralnerd]

Do you know what the structure behind it is? Is it wood? If so, the IBC in the wood section has values for shear for gyp board and sheathing. I believe it is Table 2306.4.5. It includes shear values for screws, nails, and staples. I hope that helps.

 

[Lion06]

No, I know it sounds crazy, but it is truly just into gyp.

 

[renko]

In the absence of a code value, you could always test it.

I assume its a 12mm (1/2") board with maybe a 4.0mm (5/32") screw. Hang some weights on it till it fails - I'd bet 3 bags of sugar (about 3kg (6.6lbs)) will do it.

try it a few times then stick a decent factor of safety, of say 2 or 3, for your working design load.

 

[vincentpa]

HILTI Catalog and Buildex Catalog, Simpson probably too.

 

[Lion06]

Alright,
I am considering this. I have a vertical element coming up to the underside of a gyp ceiling. The ceiling is hung from deck above and is acting as a large diaphragm of sorts to brace the vertical elements at the top.
What I want to do is put a number to what the brace force can be (from the vertical elements into the gyp ceiling).
I can't find a value for a screw into gyp only. If anyone knows where I can find this, I would greatly appreciate it. I know the bearing on the drywall will likely govern, but I would like a number to put to it.
One other thing I am considering is this: Attaching a piece of plywood (say 4' x 2') to the top side of the gyp ceiling, then attaching the vertical element to the plywood through the gyp. I am thinking this will act as sort of a drag strut to help get the out of plane load on the vertical element into the gyp ceiling "diaphragm". Once in the ceiling, I am not concerned about it.
Doing this will allow me to count on many more screws than just from the vertical element into the gyp alone.
Even doing this, I would like to have some kind of number in mind to come up with some number of screws.
Any thoughts?

 

[UcfSE]

Does a hung ceiling have enough out-of-plane stiffness to act as a diaphragm for anything? What happens in a year when the owner/contractor decides to go with acoustical tile?

 

[Lion06]

This is in a LARGE commercial building. The drywall ceiling is attached to a light gauge grid that is hung from the deck above. It also frames tightly into all of the full-height partitions. I have no doubt that this ceiling can take the small interior wind loads (5psf). I just need to make sure I can properly get the interior wind into it.
I don't think the owner will be chaning anything with the ceilng. There is no room to do anything with all of the ducts/ piping, plumbing, etc. running through.

Additionally, individual tenants may do what they want below the gyp ceiling, but the gyp ceiling is staying in place. If, 2 years from now, someone decides to rip it out, I would expect a call from them as to how they will now support this storefront.

 

[rb1957]

skyhooks and magic tape ?

 

[UcfSE]

I assumed you meant drywall attached to framing that is hung.

If you expect someone to call you two years from now about ripping out a ceiling, I think you'll get disappointed. I doubt many people think of a ceiling as structural, and certainly won't remember in two years, or care.

On an unrelated note, the 5 psf interior load is a live load, not a wind load.

In direct answer to your question, check with specific screw manufacturers as well as drywall manufacturers. They may have test data for their screws or drywall. For drywall only - I'm reading as two pieces of drywall screwed together with no other framing involved, I think you'll have trouble finding a capacity. I would expect the failure mode to be tilting instead of bearing given the weak strength of gypsum board. As far as equations, I have none for that case.

 

[vincentpa]

Go to Home Depot or Lowe's. Sometimes the screw boxes give load values on the back. I'm serious.

 

[Lion06]

Ive actually decided to go with the TOGGLER bolt from Hilti. It has shear values into hollow gyp (ableit very small).
Thanks everyone!