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Re: Code changes to amplification of ground acceleration

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Good question!  I have been wondering this for several years and could not
get anyone to give an answer (and most could not understand the
question....).  I hope you get some answers....

Mark

----------------------------	

you wrote:

I have been trying to track down the basis for changes to the
code-prescribed amplification to ground acceleration between the 1994 UBC
and the 1997 UBC (which carried over into the 2000 IBC). I've looked thru
the NEHRP Commentary (1994 and 1997) but could not find an explanation for
one of the changes made: 1. In the 1994 UBC, Section 1628.2.1 placed a
maximum value of 2.75 for the value of C as used in V=ZICW/Rw. This would
indicate a peak response of 2.75 times the ground acceleration. (However, it
is curious to me that Figure 16-3 showed a maximum amplification to ground
acceleration of 2.5?) 2. In the 1997 UBC, Section 1630.2.1 places the
maximum base shear value at V=2.5CaIW/R. (For soil type B, Ca is similar to
Z from the 1994 UBC.) This would indicate a peak response of 2.50 times the
ground acceleration. What is the basis for the reduction in the peak
response amplification relative to ground acceleration, when using the
static force procedure? William C. Sherman, PE Camp Dresser & McKee, Inc.
Denver, CO Phone: 303-298-1311 Fax: 303-293-8236 email: shermanwc(--nospam--at)cdm.com
</ym/Compose?To=shermanwc(--nospam--at)cdm.com&YY=27527&order=down&sort=date&pos=0>


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