Brian,
The first concept I present when I teach seismic protection for
sprinkler systems is to avoid doing the work of the site engineers,
soils engineers, structural engineers, or architects. Heading down that
path increases your chances of sitting in the witness chair to defend
what you've done. A decided negative all the way around.
As for the process itself, it's not quite as simple as it used to
be, as I'm sure you've learned. The USGS software forces you to
designate applicable design codes, the appropriate soil classification,
and perhaps the risk category or earthquake hazard level as well, prior
to determining the Ss value for you. Steve Leyton is correct, in that
finding the exact lat/long of a project site is fairly easily
accomplished thanks to numerous websites. The one I use most frequently
is latlong.net.
There are nine different design code reference options in the USGS
software. I know which one of those options is applicable here in
California, however, unless you're sure of what's applicable for your
specific project the results might not work out the same. The site soil
classification could be better or worse than the default value for the
calculation, which is "D". A lower letter (A-B-C) shows a much more
stiff soil, while a higher designation (E-F), shows a much less
resistant to motion parameter. You may have to enter a "risk category"
which identifies the building use, or the "earthquake hazard level",
which has four separate categories, or a custom set of parameters to
generate the information.
Now if you can, with some degree of accuracy, establish those
variables, then the USGS process can give you a reasonably accurate Ss
value. If you can't, then why are you trying to do that in first
place? The only reason I follow the process is to verify some value on
a set of plans - either from a sprinkler contractor or a structural
engineer - that just doesn't match what I've seen before in a specific
area. And, when I come up with a different value, my question is
always, "I came up with this value, which is different from yours. Can
you check my figures/parameters to see where we might be coming up with
different numbers?"
I'm not trying to tell you to run and hide, however I am suggesting
that you're taking on a liability that doesn't match the work you're doing.
The above is my opinion as a member of the hanging and bracing
committee of NFPA 13, and doesn't reflect the official position of NFPA,
which is contained in the standard, or that of anyone other than myself.
sincerely,
*Ken Wagoner, SET
*Parsley Consulting***
*350 West 9th Avenue, Suite 206
*Escondido, California 92025
*****Phone 760-745-6181*
Visit our website <http://www.parsleyconsulting.com/> ***
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