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Min. Reinf. in large pedestals

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Scott, you wrote:
>ACI 318-99 Section 10.9.1 says the minimum
>compression member reinforcement is required to be
>between .01*Ag and .08*Ag.  ACI 318-99 Section 10.8.4
>says you cannot reduce the minimum compression member
>reinforcement to .005*Ag in areas of high seismic

>Scott M Haan P.E.

OK, let's think about this for a minute.  What would
you use for Ag?  If it's the 6 meter circle, its area
is 28.3 square meters and its perimeter is 18.9 m. 
Translating into units that we Americans (and we
alone) understand, 0.5 percent of the area is 219
square inches over a perimeter of 61.8 feet.  That
works out to a #11 bar every 5 inches or so.  I know
the "T" in the T&S that you have to deal with is more
than most of ours, but do you really want to do that?

Area goes up as diameter squared, perimeter only as
diameter.  At about four foot diameter I usually stop
worrying about it and throw some reasonable
reinforcing at it.  Like #6 at a foot.  I would use a
good deal more reinforcing on the top and bottom
surfaces, but it will still be a very small
reinforcing ratio.

Mike Hemstad, P.E.
St. Paul, Minnesota

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