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RE: Redundancy R-factor and new math

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Tim,
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(--nospam--at)hughes.net>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)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


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