Gypsum sheathing diaphragm

[BadgerPE]

Good Afternoon All!

I have a little bit of a tricky situation that I am trying to deal with. What I have is a 60' x 100' building made exclusively out of cold-formed members, including the roof trusses. Two sides of the structure are adjacent to a taller PEMB building so wind loads do not apply to those two sides. Based upon the geotech report, it is in seismic category A. The issue I am having is with the diaphragm design. The trusses will have a standing seam roof applied to hat channels at 2' o.c., which is not able to transfer diaphragm shear to the shear walls. Due to the classification of the structure, non-combustible materials are required for all structural elements and therefore to sheet the top chords of the trusses and create a true diaphragm, fire-retardant plywood/osb would be required. Currently, using fire-retardant sheathing is cost prohibitive (approximately $10,000), which is a small drop in comparison to the overall cost, but nevertheless I have been given the task of finding something that works. I have approached the truss manufactures about designing a diaphragm using x-braced strapping at the top chord. They said they can but that it will be quite labor intensive and thus drive the cost up again.

So what I am looking to do is utilize the gypsum ceiling and a series of drag struts to transfer the wind load into a number of interior walls. Thus far I have not been able to locate any information regarding the design of a cold-formed diaphragm which utilizes gypsum. Does this idea sound like it may work? Am I missing something easier or is this method in violation the 2009 IBC? As it stands now, using 6 interior walls as shear carrying walls, I can get the diaphragm maximum shear down around 100 plf.

 

[spats]

First, I have to say that "ignoring" wind load on two sides because of adjacent PEMBs doesn't sound like a good idea to me, unless they basically part of the same building. Regardless, you still need at least stability bracing, unless you're physically tied into one of the adjacent buildings.

Even if there is no literature on light gauge with gypsum, it seems you could use wood framing/gypsum diaphragm numbers as long as your fasteners have a least the same shear resistance as the wood/gypsum fasteners.

 

[MiketheEngineer]

Agree with Spats and yes IBC does address this. See chapter 25 - 90 plf or 70 plf depending on fatneners.

 

[woodman88]

The 2009 IBC Chapter 25 Table 2508.5 only applies to wood framed diaphragms.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[jimstructures]

Exterior components and clading loads do not apply to those two sheltered walls. Interior components and cladding loads or minimums do apply. However the IBC does state that Main Wind Force Resisting Systems will have their respective loads applied to the frames and bracing. You can not shelter a building and reduce the MWFRS loads to the Frames and Bracing.

Jim

 

[BAretired]

I don't like the idea of a gypsum board diaphragm. NBC does not permit it. You really need a deck under the standing seam roofing capable of acting as a diaphragm. It can be a low profile steel deck, plywood or OSB.

BA

 

[MiketheEngineer]

IBC does have one for cold formed - just can't find it off hand`