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Re: R-values in Seismic Provisions

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Ronald O. Hamburger, thank you for your thoughts on this - but I am still 
somewhat unconvinced.  Your first comment relates to the "approximate period 
formulae".  But the noted R-value was not specified to necessarily be solely 
for designs using the approximate period formulae.  Some designs could use 
more accurate period calculations or could be relatively rigid structures, 
which are not impacted by the approximate formulae.  (And as pointed out by 
another responder, other features may actually reduce the actual period.) 
 
I do agree with your second comment that "Most structures incorporate 
substantial overstrength."  However, I am not sure this overstrength can be 
generalized and I am not sure whether it is typically by as much as a factor 
of 2.  Thus I would concur that reality is that full elasticity generally 
would occur at an R-value greater than 1.0 (but may not be as high as 2.0).  
This can be a significant issue if one is attempting to keep a structure 
"nearly fully elastic" in a design.  Since yielding is permitted in ultimate 
strength design, an R-value of 1.0 is certainly implied as the "theoretical" 
value for full elasticity.   
 
(The speaker said that an Rw = 3.0 used to be the estimated limit of elastic 
behavior using allowable stress design, now reduced to R = 2.0 for load
factor 
design.)