Steel Deck Diaphragm Fasteners

[wallerdf]

I'm trying to figure out the appropriate wind interaction loading on a roof deck fastener when calculating the attachment pattern.

By ASCE definition I know diaphragms are main wind and fasteners are C&C. So do I use main wind for shear loading and C&C for uplift loading and use that in the interaction equation. Or do I use main wind shear and uplift for the interaction and then check the fastener separately for pullout, pullover, etc. using C&C uplift.

Can you even combine MWF and C&C in same interaction?

 

[Ron]

Work it both ways and use the more conservative. Keep in mind the tributary area of a fastener is small. Remember that the building will react from the way it is loaded, not necessarily from the way we model or compute it.

Think about the interaction....even though a purist might consider that you wouldn't mix the two for any reason, think about what is causing the loading. For instance, if the shear is being caused by movement of the frame (diaphragm) and tension is being caused by C&C uplift, then apply those.

 

[UcfSE]

Combine MWFRS diaphragm shear with MWFRS uplift. Then check for C&C uplift. Both need to work. You don't mix MWFRS and C&C pressures together at the same time.

 

[KootK]

I vote for combining MWFRS diaphragm shear with C&C uplift pressures. When you've got your max MWFRS loads pushing your building over, there's a pretty good chance that you're also dealing with your max C&C uplift. It seems reasonable to me that they should be considered to stem from the same wind event. C&C loads are more intense to reflect less tributary area averaging for a phenomenon that varies spatially. This should apply during the MWFRS wind event just as it would apply to any other wind event.



The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[wallerdf]

Thanks everyone. I've been doing it the way UcfSE described. Combine MWF and then check C&C.

My question stemmed from a seminar I sat through and the new roof deck design manual. In their example, although they don't actually do the wind calc, they provide zone 1, 2 and 3 pressures which is obviously C&C.

The fact that MWF loads are an average pressure like you said KootK makes me believe you can have MWF and C&C in the same event. It just depends on what you are checking. Therefore using MWF for shear and C&C for uplift seams reasonable.

 

[KootK]

If there's a argument to be made for not considering peak C&C and peak MWF together, I think that it stems from directionality. I suspect that the wind direction producing the peak uplift in a particular corner is probably not the same wind direction that produces the peak MWF. I've no idea how to take advantage of that however.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.