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Re: Mat Foundation

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George Simmon,

	In the early 1980's I was the Chief Civil/Structural Engineer for an
engineering procurement construction (EPC) company which built a number
of buildings like the one you describe in Western Canada (mostly
Alberta) for the petrochemical industry.  Usually the slab was only one
foot thick with the perimeter thickened to two feet except when the
installation also supported a compressor (usually 400 to 800 horsepower
gas or diesel powered reciprocating compressors) in which case we made
the whole mat two feet thick.  We provided ground insulation for four
feet around the facility to prevent frost from getting under the
foundation since frost under the foundation could have been disastrous.
The largest of these buildings may have been 50 by 100 feet but most
were 30 or 40 feet by 60 or 80 feet or smaller.  We never used control
joints and, to my knowledge, all of the buildings performed
satisfactorily.

	A word of warning.  Our foundation conditions were generally hard clay
or gravel which was relatively stable with changes in moisture content
and relatively uniform with respect to depth.  If you have a swelling
clay or a site where part of the building will be on hard foundation
(dense gravel or bedrock for instance) and part will be on soft clay
this is probably the wrong type of foundation.  The mat you propose is
excellent for spanning small local soft spots but quite poor in
accommodating large differences in settlement characteristics.

	Hope this helps.

				Regards,


				H. Daryl Richardson

GEORGE SIMIAN wrote:
> 
> This is a pre-engineered metal building (typical 25 ft column spacing) with
> 2-1/2 ft thick mat foundation which will also serve as finish floor.  Would
> you provide control joints? Do not want to cut reinforcement which will make
> mat less effective.  Just cutting concrete will not necessarily provide
> weakened planes at those locations.  Any thoughts.  Thanks.
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