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RE: Concrete Piles w/ an R = 1.0!!

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Thanks to Gerald and Steve for the input, and, yes, it is an SDC of E. I like the idea of using an R of 2.0 per Table 15.4-2 and have used this for open decks on hillside slopes, but chapter 15 is for "Nonbuilding Structures", and it seems that I am stuck with Chapter 12, ("Building Structures"), if we are underpinning an existing structure.
 
Thanks agian to all,
 
Larry Hauer S.E.
 

From: sgordin(--nospam--at)sgeconsulting.com
To: seaint(--nospam--at)seaint.org
Subject: Re: Concrete Piles w/ an R = 1.0!!
Date: Fri, 24 Jul 2009 10:53:00 -0700

Larry,
 
On top of this, by using the Table 12.2-1 G criterion for ordinary moment resistant concrete frames, your system must be designed/detailed as such.  By the same table, such systems are not permitted in SDC C or higher (where, I presume, your project is).
 
Assuming that the piles considerably project above the ground, I would try to consider the columns as true inverted pendulum structures (similarly to what Gerard is suggesting) per ASCE Table 15.4-2, R=2.  IMO, this will still be conservative. 
 
V. Steve Gordin, SE
Irvine CA
 
 
----- Original Message -----
Sent: Friday, July 24, 2009 10:44
Subject: Re: Concrete Piles w/ an R = 1.0!!

Can't you just consider it a foundation and not a Lateral System? or is this thing sticking up out of the ground a ways?\

Does taking the reaction from the structure above and multiplying it by OMEGA (for the structure above) feasibly? This should accomplish the intent of the code (this member shall not yield)....

-gm

On Fri, Jul 24, 2009 at 10:38 AM, <lrhauer(--nospam--at)earthlink.net> wrote:
To All,

For designing an underpinning concrete pile, (caisson), foundation of an existing structure where the piles are a cantilevered element, (no grade beams at the top), ASCE Table 12.2-1 Item "G" requires an R of 1.0 for seismic loads. Can anyone give me some input on justification to use a higher R value, or am I stuck with the R of 1.0?

Thanks in advance,

Larry Hauer S.E.



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