Rigid Board Insulation Elastic Modulus

[271828]

Yeah, I know, my google-fu is weak. I've spent a half hour looking now, and give up.

Can someone grant me an estimate of the elastic modulus for typical rigid board roof insulation?

While you're at it, how about E for typical gypsum board?

Thanks in advance,
100000e

 

[SlideRuleEra]

Be careful with the units. E is in "pounds per inch", since the thickness of material tested is defined.

For 2" thick Expanded Polystyrene: E = 1300 to 1900 lb / in

For 1/2" thick Wood Fiberboard: E = 18600 lb / in

Here is the source:

http://docserver.nrca.net/pdfs/technical/327.pdf

Note: Google Time = Approx. 5 minutes

Typical Gypsum Board: E = 0.15 x 10^6 psi to 0.38 x 10^6 psi
Calculated from information (Effective Stiffness) in this source:

http://www.gypsum.org/pdf/GA-235-10.pdf

That one wasn't too difficult, either.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Ron]

Perhaps a bigger question is ..... why?

 

[271828]

Thanks SRE. I knew it must be there. Not sure how I kept missig it. Probably look at ten sites.

Ron, I have a unique application. Roof with B-deck, 3 in. of rigid insulation, air-space, pedestals, and concrete pavers. Need to do vibration analysis. With only the B-deck, there is so little connectivity between the purlins that they vibrate almost independently. Tests indicate that's not the case. Looking for whatever EI I can find to add to the deck. Pavers are in 24 in. discrete modules and are not flexurally connected to each other, so can't use them. Insulation is the only other thing and that might be enough to bring the model's modes similar to the measured ones.

I bet if you had three guesses, you would've guessed that second, right? LOL

 

[271828]

Drat. Fourth sentence should've read:

"With only the B-deck, there is so little connectivity between the purlins that the model thinks they vibrate almost independently"

 

[Ron]

271828...nope, wouldn't have guessed that one.

Look at stiffness compatibility. You have none. EI of the deck and EI of the rigid insulation are going to be vastly different with almost no composite contribution by the rigid insulation. The fasteners holding the rigid insulation to the deck will bend and locally compress the rigid insulation before you mobilize a composite action.

You have a couple of choices. One, you can add mass by a poured topping instead of pavers. You could add mass by replacing the rigid insulation with lightweight insulating concrete. This would act compositely as well, increasing the stiffness of the deck system.

Two, you could reinforce the deck from the bottom by welding or mechanically fastening stiffeners in the flutes.

One other possibility is to fill the flutes under the rigid insulation with cellular concrete, pumped from the bottom. Difficult, but can be done.

 

[271828]

Thanks Ron. All of those are good options, I think.

I was thinking of adding the EI for the deck, insulation, etc., not assuming composite. Not looking for much here, just the most accurate modeling.

 

[wannabeSE]

271828,
If you are still interested in gyp board properties the Gypsum Association has some information:

http://www.gypsum.org/pdf/GA-235-10.pdf