1/4" Self Drilling Screws in Bending

[druminman]

I am working on the light gauge stud wall design of a symphony hall that features much use of sound transmission isolation. There are occasions where the design calls for attaching light gauge framing clips to structural steel with a 1/4" thick neoprene isolation pad between the clip and the structure. These clips are loaded in shear, and it is assumed that the screws will not be tightened such that the neoprene is compressed, so there will be no tensile force in the screw, only shear and bending.

Does anyone know of a rational analysis method for such a connection? My suspicion is that the threads will lead to significant stress concentration beyond that determined from simple bending.

Thanks in advance,
Patrick

 

[CoryPad]

There is no rational analysis method for such a connection because there is no rational reason to use self drilling screws in a structural application that loads the screws in bending. Sorry, this is not to be judgmental, you just will not find published material on this subject.

 

[BauschSW]

You could investigate the Elco Dril-Flex fasteners, they aren't your typical self-driller.

http://www.tannerbolt.com/default.aspx?page=spec page&specpage=ELC

EAF876.htm

http://www.tannerbolt.com/default.aspx?page=item

detail&itemcode=ELC+EAF876

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

 

[UcfSE]

Look in the Hilti product tech guide, 4.1.8.4. There is some information and equations on bolts in shear and bending due to standoff.

 

[Jounni]

A typical anchor Gap calculation can be used for this type of connection. UcfSe's Reference (Hilti product Tech Guide) is a good reference. Note that if the gap is 1/4" or less, the bending effects can be neglected if the gap is fully shimmed.