Foam insulation under concrete floor. Compressive computations

[fastline12]

I am working on some numbers for one of our new shop buildings. We want to pour a 6" floor and will have some pretty heavy loads on it. We will have some CNC machines that weight approx 30K lbs loading into 6 point loads at the padded feet which works out to a foot print of 6ft x 10ft approx and each point load on the feet at 715psi per foot.

I realize there is a lot of design work to do in the rebar structure and concrete blend but I am having a hard time finding data on deflection of concrete to determine interactions with the EPS foam board below. It is my understanding that concrete deflection is very low so very reasonable to consider EPS for this application.

We will also have some wheeled machinery in from time to time that will easily weight 50K lbs but due to the tires footprint, the point load is actually much less. I am not sure if we need to be looking closer at total load on the floor or point loading and deflections?

Obviously I am trying to determine our margins and capacities by using EPS under the concrete pad.

 

[Denial]

You have a relatively stiff concrete slab sitting on top of a relatively compressible bed of EPS foam.[ ] If you are able to adequately represent the support the foam provides to the slab as an equivalent "modulus of subgrade reaction" (see below*) then there are analysis methods available to you.[ ] Some Finite Element software has direct element formulations for plate elements on an elastic foundation.[ ] There are design charts for the slab's deflections and bending moments for both an interior location and an edge location, called "Pickett & Ray influence charts" after the researchers who developed them.[ ] Finally (shameless unpaid commercial) I have written a pair of spreadsheets that automate the Pickett & Ray procedure, available as free downloads from my web page rmniall.com.

[super]*[/super]The "modulus of subgrade reaction" approach is also known as the "Winkler foundation" approach.[ ] Its key assumption is that the vertical pressure that the supporting medium exerts on the slab at any particular point is proportional to the vertical deflection of that point, and depends on absolutely nothing else.[ ] The constant of proportionality is called the modulus of subgrade reaction.[ ] This approach is equivalent to viewing the supporting medium as a bed of closely spaced, completely independent springs.[ ] It tends to be embraced by structural engineers but abhorred by geotechnical engineers.

 

[Tmoose]

http://www.in.gov/dot/div/contracts...d/10English/Part6/ECh62/figures/EFig62-1A.pdf

Concrete vs aluminum.
Similar densities (yet concrete is often percieved as "heavy" and aluminum as "light", concrete is about 3X stretchier, with ~ zero tensile strength and ductility