Pole Barn Metal Ceiling Diaphragm - hitting the mark

[ThorenO2]

Hello,

I am looking to install a 26 gauge metal ceiling diaphragm with trusses spaced 4'-0" o.c.. My question is do the trusses require 2x4 purlins at the underside of the trusses for panels to attach to or can the panels attach directly?

One of the pole barn manufacturer's says additional framing is needed if the truss spacing exceeds 4'-0"; however, it seems it would be difficult to hit the mark with the fasteners. With the 2x4 purlins, there's room for error. For large barns, omitting the purlins would save thousands of feet of lumber. I appreciate any input, thank you.

 

[phamENG]

That'll mostly depend on the requirements of the ceiling. 26 gauge could be flat sheets or it could be profiled - this will affect how far it can span. You say diaphragm - are you really using it as a diaphragm? If so, the in-plane shear capacity is directly influenced by the support and fastener spacing.

So I'd say no one size fits all answer.

 

[ThorenO2]

PhamEng, thanks again - panels are ribbed profile. Using it as a diaphragm to supplement the roof diaphragm. Following NFBA design example with both roof + ceiling. Fastener spacing given in ESR for diaphragm values with 4’ spacing. Problem is if they miss the mark, it won’t work.

 

[phamENG]

Got it. Well, that's an issue with all diaphragms - and I've rarely seen a building that didn't have a line of nails an inch off of a roof truss or some extra pins next to an OWSJ. It'll come down to QA/QC. Is the contractor any good? Will you have inspections? If so, do you have a means of getting into the attic safely to look for missed fasteners?

At 4' spacing, if they miss the truss, there should be a noticeable sag in the ceiling that's now trying to span 8'. Since this is an overhead application, they'll have a hard time keeping it in place if they miss the truss with the fasteners.

 

[ThorenO2]

Actually, I’m certain now they can line it up and get pretty accurate - they just draw a string or similar. It’s means & methods and won’t be a problem. No additional lumber. Saves a ton.

 

[Lomarandil]

I agree -- missed fasteners should be pretty obvious if you are able to get up to them during inspection (certainly from above, or maybe from below -- would a missed fastener turn freely?).

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just call me Lo.