Rational basis for the R value used in seismic calculations 1

[engrdon]

I think this is the correct forum to address this subject. If not, please reply with the right one.

I need a little help with the background on the developement of the R value used in seismic calculations. Has the R-value ever had a rational basis? That is, has it be quantified and validated through analysis and testing?

It seems to be rather arbitrary.

 

[Qshake]

You should check out Earthquake Engineering Research Institute's abstract database for the Earthquake Spectra. They did an article on "R" values.

The essence is R is the difference from the Elastic response to the anticipated and agreed upon inelastic response level.

This recognizes that structures generally cannot resist large earthquake induced forces elastically and therefore some level of yielding is acceptable.

Additionally, the more redundancy and ductile detailing the greater the R value since it is perceived that yielding will be in a more controlled fashion and due to redundancy the overall structure will not fail.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[WillisV]

engrdon - See pages 185-188 of the PDF file in the link below for a more involved technical discussion of the origin of R values (page 158-161 of the paper itself).

http://scholar.lib.vt.edu/theses/available/etd-05152003-171138/unrestricted/01_THESIS.pdf

Unfortunately what it boils down to is that R values are largely empirical and are heavily influenced by the committee members representing the various materials (e.g. if Concrete vs. Steel nobody wants the other to have the upper hand in R values).

 

[JStephen]

"what it boils down to is that R values are largely empirical and are heavily influenced by the committee members representing the various materials"

Not that this will keep us from calculating seismic loads to 8 decimal points!