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Re: Min. Reinforcement in Pedestals

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Karim,

Your problem is intersting but not simple.

In my opinion we have to establish the 'type' of this platform, that you are talking about, in the light of definitions as spelt out in the code, for me, its ACI 318.

COLUMN:

It certainly doesn't fit in to the definition of a column; because to be a column, " ratio of height-to-least lateral dimension should exceed 3". In your case it is 1.3/6 which is less than 3.

PEDESTAL:

Definition of a pedestal is :

"upright compression member with a ratio of unsupported height to average least dimension of less than 3".

In your case the same ratio is 1.3/6 which implies by virtue of its geometry it surely is a "pdestal".

But, for all practical purpopses, it is more of a slab, elastically resting on the soil, than a pedestal.

You should know this slab/pedestal is embedded in the soil for upto 1 m. This is providing it a lateral restraint. Its not going to move given its passive resistance advantage.

The only portion of it that is exposed is 300 mm. The rest are burried in the body of the soil.

If I were you, I would simply provide a dia 16 mm rebar @ 300 centers, on top only, both ways, to take care of temperature stresses at the top only. This rebar should provide a minimum clear concrete cover of 50 mm. And, I would not worry about any other reinforcement to be provided. This in part agreement with what Darryl earlier proposed to you.

I hope my learned friends would agree/disagree on this. Best regards,

SYED FAIZ AHMAD; MENGG, MASCE
SENIOR STRUCTURAL ENGINEER
SAUDI OGER LTD
RIYADH, SAUDI ARABIA.




From: "Karimzadegan" <struc2(--nospam--at)pidec.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <SEAINT(--nospam--at)SEAINT.ORG>
Subject: Min. Reinforcement in Pedestals
Date: Wed, 26 Dec 2001 10:55:42 +0330

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
PIDEC Co.
Shiraz
Iran




SYED FAIZ AHMAD; MENGG, MASCE
SENIOR STRUCTURAL ENGINEER
SAUDI OGER LTD
RIYADH, SAUDI ARABIA.


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