I presume that the R factor to which you refer is the response factor.
There have been a lot of changes in the path of code development. Many of
the developers that worked on the old SEAOC Blue Book, ATC, etc. are the
same ones that worked on the NEHRP Provisions which morphed into the ASCE 7.
What has changed is the evolution to the seismic spectral ordinates which
allowed us to sharpen our pencil and real earthquakes which served as test
studies to expand on testing in the lab and show us where we were wrong.
The establishment of the response coeficients are not all that arbitrary.
They are predicated on comparrisons to other systems, testing, some limited
computer nonlinear modeling, and observed behavior. Evidence is presented
to various committees and it moves through a fairly well defined process.
It is not a perfect process as many R value studies have indicated.
Good nonlinear performance is generally rewarded with high R factors. The
importance factor will not necessarily assure linear behavior. In theory an
R of 1.25 will result in linear performance, but willl induce higher
accelerations to the supported components. Many components such as
electronics can be suseptable to damage at higher accelerations.
You may wish to refer to the UFC 3-310-04 on the Whole Building Design Guide
to observe the lengths required for a facility to remain operational
following a design earthquake. It is the first document in a long time to
address the issue.
Using an importance factor was opposed by some on committees because it
created the false impression of "operational" performance. The code's focus
is on life safety. Operational capability and servicability is beyond the
intent of the code.
The US Military had to address the issue and developed the UFC 3-310-04 in
which a SUG IV class of buildings was created.
If this is of further interest you may wish to refer to:
http://www.wbdg.org/ccb/browse_cat.php?o=29&c=4
Scroll down to the UFC 3-310-04 and click on the downloadable pdf.
It is almost 250 pages long and builds from the IBC / ASCE 7.
You will see some familiar names in the credits. The main man on the
committee was Dr. Jack Hayes who is the current director of the NEHRP at
NIST.
Regards,
Harold Sprague
>From: "Pinyon Engineering" <Pinyonengineering@hughes.net>
>Reply-To: <seaint@seaint.org>
>To: <seaint@seaint.org>
>Subject: Redundancy R-factor and new math
>Date: Mon, 23 Jul 2007 12:15:09 -0700
>
>
>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
>
_________________________________________________________________
http://liveearth.msn.com
******* ****** ******* ******** ******* ******* ******* ***
* Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
* This email was sent to you via Structural Engineers
* Association of Southern California (SEAOSC) server. To
* subscribe (no fee) or UnSubscribe, please go to:
*
*
http://www.seaint.org/sealist1.asp
*
* Questions to seaint-ad@seaint.org. Remember, any email you
* send to the list is public domain and may be re-posted
* without your permission. Make sure you visit our web
* site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********