Freezer floor, column insulation options 1

[Benelli]

I am installing a Zero degree freezer in Tidewater Virginia (mud slab, gravel, forced air venting, etc) into an existing building. One of the buildings existing metal support columns is inside the freezer area and rests on a footing appx. 5 feet square with a raised concrete pedestal, appx.18 inches square and 24 inches high, in the center supporting the column.

My question/concern is: What is the proper approach to insulating the existing column to prevent eventual frost heave under the column? The final grade on the the finished freezer floor is to be level with the bottom of the column, which will also make it, therefore, level with the top of the concrete pedestal upon which the column rests. Currently of course there is no insulation or other material separating the concrete footing and concrete pedestal from the metal column.

Thanks for any information or insights. Benelli

 

[JAE]

Typical detail for freezer column support is to set the column baseplate on top of a wood blocking - usually treated oak. The wood is aligned with the underfloor insulation.

There are alternative products - we've seen some type of fiberous plastic blocking that is an attempt to replace the wood blocking. You might try some Google searches for it. Some of our clients indicated that the wood blocking was cheaper than these plastic blocks.

 

[cfloor]

Hello
Pleae, excuse my ignorance, but can someone explain (diagrams would help) the construction aspect of "setting the column baseplate on top of wood blocking"? Would not the column load "crush" the wood and/or once the wood disintegrates (being biodegradable) cause the steel column to settle thereby resulting into deifferential settlement?

Also, how much significance is there for "heat/cold" tranfering throught the steel columns into the subgrade? Can the cold (after years of exposure) cause the sugrade to heave and cause damages? Should the column footing be significantly lower that the top of the finished slab-on-grade?

 

[JAE]

cfloor - the wood used is a hardwood, like oak, that will not crush under the baseplate pressure.

Say you have a 32' x 32' bay - with DL = 16 psf and RLL = 20. The column load is about 37,000 lbs. If you have a 14" square baseplate - the compression on the wood is

37000 / 14^2 = 189 psi. pretty manageable.

The wood is treated so it won't deteriorate.

The wood is a thermal break that limits the cold from penetrating through the column to the footing and on to the subgrade. In most freezers, there is also an under-floor heating system that is located below insulation layers which are below the slab. So no heaving.

A typical floor cross section would be:
Concrete Slab
Insulation (usually about 6 to 8 inches of rigid)
Vapor barrier
10" granular material
Glycol or other heating grid system placed at midheight of the granular material
Subgrade.

So the footing is usually placed so that the top of footing is at the bottom of the granular material to allow the heating system to not be interrupted by the footing.

This usually requires a concrete pedestal to extend the top of concrete up to the bottom of the insulation so the wood blocking under the column is in line with the insulation.

 

[cfloor]

JAE, thanks for the quick and informative response. Typically, would the wood baseplate be in the 1" thickness or less?

In your opinion, what would be the consequenses should the contractor (or previous engineer) NOT recommend/install this wood blocker? Do you think that this negligence is crucial?

In this particular floor composition, the construction profile is as such:
6" concrete slab
4½" rigid insulation
vapor barrier (?)
6" concrete slab w/ heating system (I think it's electrical)
10" compacted subgrade

It's a strange effort to double up the concrete slabs, but then again...

It's now about 8 years later and the building owner is witnessing some major slab fissures. I'm wondering if the rigid insulation (I don't know its brand name yet) began to fail in compression thereby causing the top slab to settle differentially, or the heating system failed. I will investigate this warehouse next week.

 

[JAE]

Wood block thickness is usually 3 1/2 to 4 1/2 inches thick.

Slab problems - yes, could be the insulation - depending on the rigidity of the insulation used.