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RE: Rho, Rho, Rho your boat (foundation)

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Logical argument: Where does the code (ASCE 7-05?) say you "don't" need to apply rho to the foundation?
Section 12.3.4: Rho applies to the seismic force-resisting system - does your foundation resist seismic forces?
Section, "Conditions where value of rho is 1.0": "Foundations" are not listed here.
The code doesn't need to list every element rho applies to.  It applies to seismic resisting elements unless otherwise "excluded".
Bill Sherman

From: Garner, Robert [mailto:rgarner(--nospam--at)]
Sent: Tuesday, August 19, 2008 10:22 AM
To: seaint(--nospam--at)
Subject: Rho, Rho, Rho your boat (foundation)

I'm designing a steel framed structure in Seismic Category D.  For the steel framing, Rho will be 1.3.  For the foundation (a concrete mat foundation), we are using a Rho of 1.0 - our reasoning being that the purpose of Rho is to assure that no single seismic force resisting element above the foundation (the building frames) will likely fail in an earthquake.  Nowhere in the Codes can I find a statement that Rho is to be applied to the foundation.  Can anyone challenge me on this with a Code quote or logical argument?


Thanks for any help you can offer.



Bob Garner, S.E.


R. Garner

Moffatt & Nichol

Tel.:  (619) 220-6050

Fax.: (619) 220-6055

e-mail: rgarner(--nospam--at)