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RE: Min. Reinforcement in Pedestals

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Something 6m (~20 ft) in diameter and 1.3m (~4 ft) thick with only .3m (~1 
ft) protruding above ground looks more like a thick slab to me rather than a 
column or a pedestal.  Therefore, I would reinforce it as a slab, not as a 
column or pedestal.  Without running any numbers, it would seem that 
temperature and shrinkage would be a concern as well as any stresses produced 
by vibrating machinery.  Circumferential reinforcing would be prudent if the 
machinery is producing any significant vibration.  It is difficult for me to 
conceive compression as a controlling factor and with a thickness to diameter 
ratio of 1.3:30, bending certainly shouldn't be a factor.


A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Daryl Richardson wrote:

. > Karimzadegan,

. >         Unless you can find some code requirement to the contrary or some
. > loading that requires greater reinforcing I would be inclined to use #6
. > (20 mm diameter) bars at 12" (300 mm) each way on all exposed surfaces.

and Scott Haan 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.

In response to A. Karimzadegan's post:

> I have a question regarding the Min. reinforcement which we shall use
> for the large pedestals. The question is the for the pedestals under a
> large equipments (e.g. 6~7m in Dia. ) we need to construct a pedestal
> to reach to the required elevation ( e.g. from -1.000m below ground to
> 0.300 above ground with 6m dia. pedestal ). It seems that application
> of about 1% or even 0.5% reinforcement is very large and unnecessary
> and in these cases the pedestal action is more close to a foundation (
> for which the main reinforcements shall be top and bot. bars instead
> of vertical bars ) instead of column action. If anyone have any useful
> suggestion in this regard, please let me know.
> Best Regards,
> A. Karimzadegan
> Shiraz
> Iran

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