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# Re: Redundancy R-factor and new math

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Redundancy R-factor and new math
• From: "Gerard Madden, SE" <gmse4603(--nospam--at)gmail.com>
• Date: Mon, 23 Jul 2007 12:48:10 -0700

When you say R factor, you are referring to the structural system factor, not the "redundancy factor" which is normaly called "rho", correct?

Have they changed the terminology?

The Omega Factors (the 2.8) are to make sure that certain elements are not the weak link in the load path (i.e. collectors won't fail before shearwalls they load deliver to fail).

To design for elastic behavior, R=1

HTH,
-g

On 7/23/07, Pinyon Engineering <Pinyonengineering(--nospam--at)hughes.net> wrote:

Hi
I was looking at some APA test of plywood shearwalls see that the saftey
factors ar for 2.8 to 3.5 for the testing to the ultimate load capacity.
Then I looked at my enercal software that fits with the 2003 IRC and now
plywood shearwall get a R of 6.0 where the 2001 california building code
(1997 UBC) gives them a R of 5.5. the Redundany value reduces the earthquake
forces based on the type of system to be used.(Iknow the R is made by
comittee not by "science")  While we use the chosen system at with a safety
factor applied to the ultimate load capacity of that system.  I know we
design to a code that is for life safety and looks to design for the big one
at the "near colapse level" . is the difference in the R=5.5 and the 2.8 to
3.5 safety factor made up in reducing the building peroid thru damage so
then the force on the building is less?  If I am to design an addition to a
fire station then the importance factor makes sure that everything remains
elastic thus no damage and the facility remains operational?

Tim Rudolph
Pinyon Engineering
Bishop CA

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