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RE: Philosophy: Seismic Design Standards

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Yes, the commentary to the SEAOC Blue Book and ATC-19, "Structural Response 
Modification Factors," both describe the method in which the response factor, 
R, was developed, and both indicate that all it did was take the K 
coefficients between the extremes, 1.33 buildings and 0.67 buildings, and 
manipulate the formula, modifying some other factors, to come up with 
approximately the same answers for 1.33 buildings, 1.0 buildings, 0.80 
buildings, and 0.67 buildings.

Rationality?  Experience showed that using (ZIKCS)W, 0.67 buildings (ductile 
steel and concrete) buildings performed well, 0.80 buildings (dual steel and 
concrete) buildings had performed well, 1.33 buildings (shear wall 
buildings, aka "box") had performed well, so the coefficients were about 
right, so they shouldn't be changed.  And they weren't changed, just put in 
another form, consistent with the form in ATC-03, to give the same answer.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Bill Sherman wrote:


Actually, Rw is 8/K.  But the simple act of moving the coefficient to the
denominator improves the formula by identifying the coefficient more
directly with a structural property.  

Following is a conversion from the "old UBC" formula to the "new" formula,
that I developed a number of years ago; the "new" formula has changed some

V=ZIKCSW can be converted to the new formula by replacing the coefficients
with the following: 
        Z=2.5*Z  (e.g., 2.5*0.40=1.0 zone factor)    
        C=C/20   (e.g., CSmax=2.75/20=0.14)    
        K=8/R    (e.g., 8/6=1.33 for shear walls)    
so: Z=ZIKCSW=(2.5*Z/)I(8/R)(C/20)SW=ZICSW/R. 
(Based on the SEAOC Commentary.)   

> -----Original Message-----
> From: Roger Turk [mailto:73527.1356(--nospam--at)]
> Sent: Wednesday, January 19, 2000 6:36 PM
> To: seaint(--nospam--at)
> Subject: RE: Philosophy: Seismic Design Standards
> Bill Sherman wrote:
> >>Code formulas and coefficients should correspond to 
> identifiable quantities.
> This is one area that I think improvements have been made in 
> the seismic
> codes over the years, e.g. I couldn't relate to "K" in the 
> formula ZIKSW,
> but I can relate "R" to ductility in the formula ZICW/R; and 
> I can relate to
> Aa=0.40 better than "Zone 4".  Also, commentaries and design 
> examples help
> greatly when trying to interpret the real purpose of code language.<<
> R is simply 1/K!  And was developed that way so that the 
> results of the 
> formula wouldn't change.
> "A rose is a rose ..."
> A. Roger Turk, P.E.(Structural)
> Tucson, Arizona