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RE; Slab on grade

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Dick

Agreed it will cost more to increase the distance between joints.  My point
was that we should choose the approach that was appropriate for the
situation.  

In this case we have an owner who wants as few joints as possible and yet
the majority of the responses did not even consider the possibility of
fewer joints at the expense of more reinforcement.  Maybe Phil is willing
to pay for the added quality.  Should we not give our clients an option?

As far as the loading criteria is concerned, it appears that the contents
of this storage building are very similar to the vehicles that would be on
a private runway.  "Use will be for planes less than 3200#, plus dump
trucks, backhoes, and any other toys my wife acquires."  Admittedly the
dynamic loads are probably not as high, which would probably translate into
a thiner slab than proposed, which in turn might offset some of the cost.

I have just looked in Fintel's "Handbook of Concrete Engineering" and find
that a lower safety factor is used for the central portion of the runway
than is used for aprons and taxiways.  This is because "..the number of
stress repetitions at one location on a runway will be much lower than on
taxiways..".  The article further states that normally the steel ratio is
about 0.6%.

I would recommend to Mr. Hodge that he read this article since it addresses
issues such as the subgrade as well as pavement design issues for both
roads and runways.  The selection of the thickness of the slab is very much
a function of the quality of the subgrade and the strength of the concrete.
 Failure to provide a proper subgrade could result in an un-economic early
failure of the slab.

Why did none of us address the issue of the subgrade?  Did we (myself
included) have blinders on?

Mark Gilligan, SE
markkgilligan(--nospam--at)compuserve.com