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RE: Concentrated Load at Edge of Pedestal

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Here’s another way to look at it.


Concrete strength, f’c is based on compression testing of a concrete sample with zero edge distance all around.  The allowable bearing stress of Section 10.17 takes f’c and reduces it by two factors – f and 0.85.   It seems like Section 10.17 must take into account the condition that you are concerned about.




Nels Roselund, SE

South San Gabriel, CA


From: Mike Zaitz [mailto:mzaitz(--nospam--at)]
Sent: Thursday, July 20, 2006 4:05 AM
To: seaint(--nospam--at)
Subject: RE: Concentrated Load at Edge of Pedestal


Not sure I classify it as a problem or more of a concern.  The bearing pressure is fairly low  (as the loads are) and fall well within the bearing pressure for 10.17.  The concern I have is that with the column being so close to the edge of the pedestal; there is the possibility of breaking off the edge of the pedestal (bursting or maybe the proper term is confinement failure).  Something similar to the failure that can occur with horizontal forces in anchor bolts near the edge of a pedestal that does not have enough ties. 

-----Original Message-----
From: S. Gordin [mailto:mailbox(--nospam--at)]
Sent: Wednesday, July 19, 2006 6:50 PM
To: Seaint@Seaint. Org
Subject: Re: Concentrated Load at Edge of Pedestal



I am not sure if I understand your problem.  The bearing pressure under the baseplate is easily calculated, and then compared to the one available from the pedestal.  ACI formulas are quite old, and proven to work for small and large pedestals, high and low loads.  For example, look at ACI318 Section 10.17 and Fig. 10.17 - if this is your case, you are going to be OK by checking the bearing pressure.


According to PCI "Notes on ACI318", reinforcement to "transfer excess loads" "must be provided" "when the bearing strength is exceeded."  In order to have this condition, thought, you have to have something really exotic going on.


Steve Gordin SE
Irvine CA


On Mon, 17 Jul 2006, Mike Zaitz wrote:

> I have a condition where I will have concentrated loads near the edge of the
> concrete pedestal under some latticed columns.  The pedestal is 4'-0" x
> 2'-0" with 2-W14x43 columns with the webs parallel to the short dimension.
> The centerlines (parallel to the web) are only 5 inches from the edge.  For
> this case my factored load is only 157 kips but on other areas they will be
> higher.  I have checked the bearing for the concrete and am trying to find
> anything for verifying that I will not spall the edge of the pedestal.  I do
> not find anything in the code (ACI 318-99) that addresses this condition
> (other than the concrete bearing).  Is there something I am missing?

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