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Re: Concentrated Load at Edge of Pedestal

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Of course it is not "your problem", I meant - it is an engineering problem you are trying to solve.
Look at the referenced ACI picture; if bearing stresses are low, you have nothing to be concerned about.  Same thing happens with the anchor bolts - if the stresses are low, you do not have to worry about anchor failure. 
It should be noted, however, that in shear or tension (anchor bolt) condition, we have such thing as a minimum edge distance; in the subject condition (if I understand it correctly), it is compression only, so the pedestal may theoretically be of the same size as the baseplate, and still be OK.
So, you may use 3D FEA analysis or just rely upon the ACI data - the time spent will be different, the result will be the same.
Steve Gordin SE
Irvine CA
----- Original Message -----
From: Mike Zaitz
Sent: Thursday, July 20, 2006 4:04 AM
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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