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RE: Min. Reinf. in large pedestals

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I didn't write the code [I have made engineer's from Minnesota change their
plans because of what it says].  For a caisson it might not be reasonable,
but then again I am pretty sure off the top of my head they did 1% for the
local airport caissons even though I did not make them and it probably was
not required for strength.  

1% is reasonable for "small" pedestals in most building design.  Where I see
it as an issue alot locally is for foundation pedestals for pre-manufactured
metal building foundations.  




Scott M Haan P.E.
Plan Review Engineer
Building Safety Division 
Development Services Department
Municipality of Anchorage
http://www.muni.org/building
phone:907-343-8183  
fax:907-249-7399
mailto:haansm(--nospam--at)ci.anchorage.ak.us



-----Original Message-----
From: Michael Hemstad [mailto:mlhemstad(--nospam--at)yahoo.com]
Sent: Thursday, December 27, 2001 9:59 AM
To: seaint(--nospam--at)seaint.org
Subject: Min. Reinf. in large pedestals


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
>risk.

>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.
TKDA
St. Paul, Minnesota




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