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RE: Philosophy: Seismic Design Standards
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- Subject: RE: Philosophy: Seismic Design Standards
- From: Roger Turk <73527.1356(--nospam--at)COMPUSERVE.COM>
- Date: Thu, 20 Jan 2000 11:18:12 -0500
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 since. 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)compuserve.com] > Sent: Wednesday, January 19, 2000 6:36 PM > To: seaint(--nospam--at)seaint.org > 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.<< > > Most AMAZING! > > 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 =-=-=-=-=-=-=-=-=-=-=-=-=-
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