Rigid Polyurethane Foam Load Carrying Capacity
Rigid Polyurethane Foam Load Carrying Capacity
(OP)
Greetings,
A local manufacturer is working on a rigid foam tank pad that would go under petroleum storage tanks. They have a data sheet on the material that indicates a compressive strength of 25 psi and actual test data that indicates a flexural strength of 60 psi and a modulus of elasticity of 1220 psi.
They asked me if I could tell them what the load capacity of a 14" thick piece by 12' diameter piece of this material is.
It's been a long time since mechanics of materials for me, and I've already told them that this wasn't something I felt comfortable doing, but I am still curious about how one would go about this process given the above information. Can anyone explain it to me?
Thanks,
Kurt
A local manufacturer is working on a rigid foam tank pad that would go under petroleum storage tanks. They have a data sheet on the material that indicates a compressive strength of 25 psi and actual test data that indicates a flexural strength of 60 psi and a modulus of elasticity of 1220 psi.
They asked me if I could tell them what the load capacity of a 14" thick piece by 12' diameter piece of this material is.
It's been a long time since mechanics of materials for me, and I've already told them that this wasn't something I felt comfortable doing, but I am still curious about how one would go about this process given the above information. Can anyone explain it to me?
Thanks,
Kurt






RE: Rigid Polyurethane Foam Load Carrying Capacity
RE: Rigid Polyurethane Foam Load Carrying Capacity
Dik
RE: Rigid Polyurethane Foam Load Carrying Capacity
Again, I've pretty much washed my hands of this, but I'm still curious about the process one would go through in analyzing this situation.
Thanks.
RE: Rigid Polyurethane Foam Load Carrying Capacity
From reading the info from Dow and similar, it appears that the compressive strength is rather high, but I would be concerned with punching (small bearing areas).
I have gotten some flak from county officials - "This isn't a structural material". but I haven't had any issues in using it for a uniform bearing condition.
RE: Rigid Polyurethane Foam Load Carrying Capacity
Thanks.
RE: Rigid Polyurethane Foam Load Carrying Capacity
I would be sure to protect that insulation material from UV and any other environmental degradation. Otherwise, you problem description leaves too much to the imagination for a very explicit answer. At the moment your only answer can be 25psi, as a uniform load, with some factor of safety. Are they trying to keep the heat of the fluid out of the soil or visa-versa? Otherwise, a compacted 10-12" sand cushion will probably be cheaper. 14" thick insul. and 12' dia. must be based on something that they’ve cooked-up, what are those constraints? What are the soil conditions and the tank construction? You should have no problem imagining that a steel floor plate in the tank should cause something less than 3.6kips/s.f. Some subgrade cushion and the rigid insul. should not be phased by a few protruding 1" round rocks; a 12" round conc. pile, in a swamp would be another matter. But, what do you do at the tank wall where the loads are in kips/lin.ft. and concentrated immediately below the shell? The insul. probably can’t take this and it shouldn’t be exposed out there anyway. You have to design your foundation (&/or tank) to distribute any concentrated loads to the insul. at less than 25psi.
RE: Rigid Polyurethane Foam Load Carrying Capacity
thread507-359119: Strength of polystyrene
RE: Rigid Polyurethane Foam Load Carrying Capacity
As I stated earlier, the tanks will hold a petroleum product. They will be located within a secondary containment system that is lined. The polyurethane pads will be placed on the top of the liner (which will be on the top of the soil). The idea of the pads is to provide a uniform surface to place the tanks on.
I'm not sure where the 14" depth came from. Actually, that's what I'm trying to reconcile in my mind. Based on the tank volume and footprint, 25 psi will be more than adequate (with a factor of safety). I'm just trying to understand what role the thickness of the material plays. For instance, would a pad made out of the same material only 1" thick have the same load capacity? The area would be the same.
Another factor that I know must be considered is the wind loading on the tank. I would expect it to produce a non-uniform load distribution on the pad (which I can easily calculate).
I'm really just curious how one goes about calculating the thickness of a material (whether it be foam or concrete or whatever) required to generate it's rated compressive strength. That's the bottom line.
Thanks.
RE: Rigid Polyurethane Foam Load Carrying Capacity
RE: Rigid Polyurethane Foam Load Carrying Capacity
RE: Rigid Polyurethane Foam Load Carrying Capacity
RE: Rigid Polyurethane Foam Load Carrying Capacity
Among other things I would be concerned about lateral loads, any time I use foam fill I typically have side walls that stabilize the slab that I am putting over the fill.
RE: Rigid Polyurethane Foam Load Carrying Capacity
RE: Rigid Polyurethane Foam Load Carrying Capacity
Here in SoFla, the stuff decomposes to sticky crumbs, in unstressed, indoor, dark, air conditioned storage, in a year or two.
I wouldn't use it for a structural anything.
Mike Halloran
Pembroke Pines, FL, USA
RE: Rigid Polyurethane Foam Load Carrying Capacity
RE: Rigid Polyurethane Foam Load Carrying Capacity
As for analysis, I would look at it as an elastic layer in a multilayer system....similar to pavement analysis. You have the mechanical properties, plug and chug as a layered elastic system. Check Witczak or other pavement analysis/design texts for examples.
hokie66...stop that! I read a post, I jump to potential failure modes (since that's mostly what I do), settle on something and then read the posts only to find you nailed it before me...happens too often!.....can I at least claim great minds think alike?
RE: Rigid Polyurethane Foam Load Carrying Capacity
RE: Rigid Polyurethane Foam Load Carrying Capacity
One is more durable.
I forget which.
Mike Halloran
Pembroke Pines, FL, USA
RE: Rigid Polyurethane Foam Load Carrying Capacity
Quick primer on some different products out there. There are specific foam panels designed for load bearing applications as the OP indicated. Besides in nearly every flat commercial roof, the other use structurally I have seen is to build up a structural floor slab to a different height without adding significant dead load. Then you top it with concrete.
Also in Florida, injectable polyurethane (similar to Great Stuff that comes in a can) has become popular in the last few years as a soil improvement and foundation stabilization method.
http://www.uretekholdings.com/about/the-uretek-met...