self tapping screws to aluminum - design value?

[frogit22]

Does anyone have a resource for attaching a self tapping steel screw to an aluminum skylight girt?

I am looking for some pullout and shear values and how to specify the screw for attachment of some curtain wall.

thanks!

 

[port125]

Hilti makes a screw called the Kwik-Flex self drilling screw that has some data for aluminum. This is the only one I know of that has loads on aluminum available.

 

[IceNine]

The following publication is very useful:

"AAMA TIR-A9: Metal Curtainwall Fasteners"

It gives values for different grade screws in different types of materials.

You can purchase it from the AAMA website.

 

[frogit22]

the Hilti published data is just what I was looking for. thanks a lot.

 

[Ron]

frogit22...keep in mind that the Hilti fasteners are STEEL, not STAINLESS STEEL. Even though they are touted as corrosion resistant, they will corrode when in contact with aluminum.

Use stainless steel fasteners. The pullout values will still be close, since the fastener will usually fail the aluminum in pullout, not the other way.

 

[frogit22]

this is in an interior environment. i would venture that the galvanic action is not much of an issue in this case.

do you agree?

 

[Ron]

No. It will eventually be an issue, even inside. Ambient humidity is enough electrolyte, and aluminum has a tendency to be cooler than surrounding materials, thus is usually the first to experience condensation.

 

[IceNine]

Several years back I worked for a company that performed curtain wall calculations for high profile projects. We generally specified Elco Dril-Flex self drilling fasteners with stalgard finish. Check out the website, they give allowable shear and tension for attachment to aluminum.

http://elcoconstruction.com/products/catalog/drilflex.pdf

 

[IceNine]

Actually, the values given in the table are Ultimate values, not allowable.

 

[ash060]

All the design requirements for screws in aluminum are in the Aluminum Association Design Manual.

If the screw is exposed than stainless steel or aluminum screws are required. If inside you can use coated steel screws. Check section J.5.1 of the aluminum specification.

I would not recommend using aluminum screws as the heads tend to pop off if too much torque is applied by the drill and it does not require too much more for this to happen. There are several limit states for aluminum screws including pull-over and tiliting which may not be covered in the Hilti book.

 

[frogit22]

http://www.lightmetalage.com/PDFs/LMA-2009-04-040_PullOver.pdf

here is a resource for pull over.