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RE: spectral response acceleration definition
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- Subject: RE: spectral response acceleration definition
- From: "daneshvar.ahmad" <daneshvar(--nospam--at)pidec.com>
- Date: Wed, 4 Jan 2006 09:32:17 +0330
Dear Bruce, Hi, I believe the first and third paragraph
is completely right, But there is a misunderstanding in the second one. My comment
is as follow: We need short (0.2 sec) and long (1.0 sec)
period “spectral response acceleration” to construct “response
spectrum curve” accordingly. Short period spectral response acceleration Ss
is similar to Ca in 97 UBC.( as a measure of constant acceleration part of
response spectrum curve for relatively rigid structures with short period), and
long period spectral acceleration S1 is similar to Cv in 97 UBC (as a measure
of constant velocity part of response spectrum curve for relatively flexible
structures with long period). Therefore, after constructing of response
spectrum curve the spectral response acceleration for other periods to be
extracted from this curve. Code permits to evaluate the Ss and S1 for location between
the contours of the maximum considered earthquake ground motion’s maps by
interpolation. Have a good presentation! Regards, From: Bruce Holcomb
[mailto:bholcomb(--nospam--at)brpae.com] I have been having trouble with the term “spectral” in
“spectral response acceleration”, so I’ve been doing some
studying. Can someone verify my findings below? Or set me
straight? I’m supposed to give a presentation at my office and I
want to make sure I have it straight before I try to explain to others. The “spectral response
acceleration” plotted in the “Maximum Considered Earthquake Ground
Motion” maps in the IBC is an acceleration with an annual probability of
exceedance of 2% in 50 years (return period of 2500 years) and is for a site
class “B” soil. The spectral response acceleration is derived
from many possible earthquakes of various magnitudes at various distances from
the site. The spectral response acceleration is
plotted for period of 0.2 seconds and 1.0 seconds because these two periods
encompass most building periods. Periods between these values (and to a
certain extent beyond these values) can be interpolated (extrapolated). The reason the “design spectral
response acceleration” is 2/3 of the “site adjusted spectral
response acceleration” is that the lower bound estimate of the margin
against collapse is a factor of 1.5 (approximate… judged by
experience). Therefore, the “design” earthquake ground motion
is 1/1.5 (2/3) of the maximum considered earthquake ground motion because we
want to prevent collapse, but the construction cost would be too great, if we
designed to prevent all damage to a structure. Bruce |
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- From: Bruce Holcomb
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