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Re: Heavy line loads on thin slabs on grade

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I think that Stan hit on the thing that I was going to point out...the
real issue is what is the soil/fill below the slab.  Since it is a slab on
grade, in theory the slab does nothing other than transfer the load for
the soil (in reality, the slab will contribute some resistance in
bending...which will help distribute the load "outward" from where it is
applied).  If the soil below the slab is good and well compacted, then you
may not have an issue.  In general, if it were me, I likely would not have
much of an issue with doing it (slabs on grade can take rather significant
loads in general).  The one concern that I would have would be the
potential for differential settlement between the two rails of the system,
which could cause the system to not function properly.  So, to a large
degree, I am not sure I see too much of a life safety issue (unless the
system not functioning properly could cause to move unexpectedly when
someone in between the stacks), but there could definitely be some
servicability issues.

Do you have any idea of the actual soil parameters (i.e. did they or could
they do a soil boring at the file system location by coring a hole?)?  If
you have a soil subgrade modulus, then you could do some approximate model
in your analysis software of choice (i.e. the old beam on continuous
spring foundation problem).  Checking against bearing capacity does not
help all that does help some if the soil report has what the
theoretcial settlement is estimated to be at that bearing load, but still
not nearly as much as doing some sort of beam or mat on a elastic


Adrian, MI

On Wed, 30 Aug 2006, sscholl2(--nospam--at) wrote:

> I suggest that you consider using pavement formulas from a highway design book. The capacity depends greatly on the density of the material under the 4" slab. Also the capacity greatly depends on the edge distance.
> I will never forget a plan checker who wanted me to do calcs. for a 250# air conditioner which was to sit on top of a non-bearing wall on a slab with no footing under. I did a calc. using pavement analysis and found it would take about 4000#.
> Stan Scholl, P.E.
> Laguna Beach, CA

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