Wood Diaphragm Question 1

[Lion06]

I have two questions about wood diphragms that I would like to get some opinions on.
I have not had a formal wood design class, but have done some wood design and read a lot from Breyer's "Design of Wood Structures ASD/LRFD".
The first question is regarding the diaphragm attachment to the joists. The tables in IBC all give nailing requirements. If you wanted to use screws to decrease the likelihood of squeaky floors down the road, is it simply a matter of making sure the screw shear meets or exceeds the nail shear or do you have to consider other things (such as ductility of the fasteners)?
The second question is regarding the chord members. Breyer's book says that the chord members are designed for teh axial forces resulting from the moment in the diaphragm. This makes sense, however, would you consider teh deflection of the diaphragm couled with the axial compression to design for the axial compression and a resulting moment equal to the compression times the deflection of the diaphragm? I know the deflection may be small, it seems like this should be accounted for, after all you don't have that axial compression without the deflection of the diaphragm.

 

[DaveAtkins]

I agree with your approach for substituting screws for nails, and I would not worry about ductility.

No one (that I know of) worries about second order moments in diaphragms.

DaveAtkins

 

[COEngineeer]

StructuralEIT, I also heard from Simpson Hanger representative that facemount hangers squeak less. Plus the installation is as easy as top flange due to the 2 teeth.

 

[Lion06]

COEngineer-
I was talking about squeaking from the nails attaching the plysood to the joists working their way loose 10 years down the road. I know some people glue the plywood to the joists in addition to nailing it, but I would like a more positive connection. I think the screws would help stop squeaking more than anything else.
That is good information to have about the hangers, too. I didn't know you got squeaking from the joists on the girder, but I learn everyday. I am trying to soak up as much as possible of this sort of stuff that you don't learn in school.

 

[UcfSE]

Screws are less ductile than nails so if you're in a high seismic region or one than requires consideration of the fastener ductility you may not be able to make the substitution without due consideration, if you're even permitted to do so.

You're second question soulnds like a p-[δ] effect for the chord. I've never heard of doing this but I don't see anything wrong with trying it, espcially to learn. I think what you'll find is the resulting difference is negligible and not worth the extra effort.

 

[Lion06]

I know that screws are less ductile than nails, but (and this may be my lack of extensive design with wood fasteners) I haven't seen anything in NDS (or similar) that quantifies the required ductility of a fastener for use in diaphragms.
If I did find that information, where would you find information on the actually ductility of the screws to see if they would meet this criteria?

 

[Boiler8019]

I'll just point out that APA's squeak free guidelines dont include screws. They focus on the details of the panel joints, glue application, glue type, and give basic nailing patterns.

I would guess the ductility of the system is affected more by the glue than the nails.