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Soils Reports under CBC 1802.2

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I keep hoping to find a loop-hole....

Section 1802.2.7, item 2, Exception states:  "A site-specific study need not
be performed, provided that peak ground acceleration equal to (S-sub-DS)/2.5
is used, where S-sub-DS is determined in accordance with Section 21.2.1 of
ASCE-7"

The above exception *looks* like it's intended to let you "over-design"
(GOD, I hate that term...) for seismic and avoid having a site-specific
soils report.  BUT--  when you go to Section 21.2.1 of ASCE-7, there is no
mention of S-sub-DS.  In fact S-sub-DS is barely mentioned in Chapter 21 at
all.   Chapter 21 deals with site-specific accelerations anyway, so this is
sort of a circular argument ("you don't need a site-specific soils survey if
you have done a site-specific soils survey").

Could it be that the reference to Section 21.2.1 is incorrect?  If so, which
section should be referenced instead?

Thanks for any hints....

Our office is hoping that reports from the Natural Resources Conservation
Service (NRCS, part of the US Dept of Agriculture) website will be
acceptable for 'run-of-the-mill' projects.  They give the USCS soil types of
SM, GP, SW, etc. that can then be cross-referenced with IBC/CBC Table 1804.2
for soil bearing values.

The NRCS "Web Soil Survey" site is:
http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx
You might have to go to this site first to load the application:
http://websoilsurvey.nrcs.usda.gov/app/
I have not spent too much time there, but it has an *amazing* amount of
info.  We all paid for it---can we at least USE it now, please??

Thor Matteson
www.shearwalls.com


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