Calculating Deflection for Gypsum Shear Wall
Calculating Deflection for Gypsum Shear Wall
(OP)
I have a single-story modular building that has a sidewall that is full of holes, and therefore I assumed the diaphragm to be rigid and have a (3) wall lateral force resisting unit. The diaphragm is light-gauge steel with a plywood decking. The walls are light-gauge with gypsum sheathing.
To validate the assumption of a rigid diaphragm, I am calculating the diaphragm and shear wall deflections. This is fine for the roof using deflection equations found in AISI Lateral Design, but I have found no equation for calculating deflection for a gypsum sheathed wall.
I would appreciate any suggestions.
To validate the assumption of a rigid diaphragm, I am calculating the diaphragm and shear wall deflections. This is fine for the roof using deflection equations found in AISI Lateral Design, but I have found no equation for calculating deflection for a gypsum sheathed wall.
I would appreciate any suggestions.
Juston Fluckey, E.I.
Engineering Consultant






RE: Calculating Deflection for Gypsum Shear Wall
As for the deflection of a gyp SW, I will have to look further in my "stuff"...
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Calculating Deflection for Gypsum Shear Wall
I will be assuming the diaphragm is rigid if the diaphragm deflection divided by the shear wall deflection is less than 2.
I haven't had an issue like this yet, but once it is resolved I will be adding it to my "stuff". Thanks for your help.
Juston Fluckey, E.I.
Engineering Consultant
RE: Calculating Deflection for Gypsum Shear Wall
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I strongly encourage you though, to consider using plywood in lieu of GSB, as, if you are in a high seismic or wind zone, these deflections calculated will only be applicable to the first event, not subesequent events.
You have to remember that with GSB, the nail holes work and become less effective in shear with each event. Hence the reduction in values for seismic loads.
I will keep looking...
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Calculating Deflection for Gypsum Shear Wall
Equations per AISI Standard - Standard for Cold-Formed Steel Framing- Lateral Design:
Δv = (ω1*ω2*v*h)/(ρ*G*t)
Δn = ω15/4*ω2*ω3*ω4*(v/0.00290*β)2
I am assuming the omega, rho, and beta factors are present because of the way Plywood and OSB are graded. A quick look at the omega factors show they are less than or equal to one, so ignoring them would be conservative (for wood sheathing applications). I haven't found the values of the shear modulus for gypsum and fastener deformations under load.
Juston Fluckey, E.I.
Engineering Consultant
RE: Calculating Deflection for Gypsum Shear Wall
A little bit of moisture/water and gyp assemblies fall apart (ie storm events with lots of rain that can last 24 hours+). I would be reticent to ever use them except maybe for the lightest of interior shear walls, I would run away from using them as my primary MWFRS for a hazardous material storage building!
Just my two cents.
RE: Calculating Deflection for Gypsum Shear Wall
A little off topic here as I was looking for suggestions for calculating the drift of a gypsum on light gauge framing shear wall.
Juston Fluckey, E.I.
Engineering Consultant
RE: Calculating Deflection for Gypsum Shear Wall
RE: Calculating Deflection for Gypsum Shear Wall
I have discovered that the studs are welded to the tracks instead of being pinned, so I have decided to use the studs as an ordinary moment frame (this oversight will be reflected in their bill, so hopefully they will decide analysis shouldn't be demanded until their drawings are complete). Redundancy is accounted for and construction doesn't need to change. Thanks for participating in my thread.
Juston Fluckey, E.I.
Engineering Consultant
RE: Calculating Deflection for Gypsum Shear Wall
With a safety factor of 3 it has an allowable racking strength of 218 PLF when used with 18 Ga. steel studs at 16"c/c.
It is a fiberglass reinforced gypsum sheathing.
Obviously you can get higher values with OSB sheathing but the DensGlass is about twice as strong as regular gypsum sheathing. IBC allows 90 PLF for 1/2" gypsum board for wind but only 45 PLF for seismic.
RE: Calculating Deflection for Gypsum Shear Wall
RE: Calculating Deflection for Gypsum Shear Wall
Juston Fluckey, E.I.
Engineering Consultant
RE: Calculating Deflection for Gypsum Shear Wall