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RE: Soil report seismic acceleration minimums??

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I have just run into this exact situation.  I have received a soils report
that, unsolicited, gives maximum ground accelerations with no explanation as
to probabilities, return periods, etc.  I am used to a full and separate
seismicity study, if it is merited and requested.  Your message prompted me
to give the geotechnical engineer a call.

The response was that this is an issue of disclosure and, you guessed it,
protection against lawsuits.  It is safe to say that almost no homeowners
are familiar with the philosophy of considering inelastic action and
allowing some structural damage for major earthquakes.  More often than not,
a Type V building is a calc and sketch job so that the owner never even
interacts with the structural engineer, who may or may not discuss this
philosophy.  This soils engineer now puts a maximum possible ground
acceleration in his soils reports so that no one can come back later and say
they were not informed that the ground motion could be so high and that
their home could sustain major structural damage.  Apparently, this is the
reason for a fair number of lawsuits after the Northridge earthquake.  It
seems that we may need to do a better job of educating the public as to
expectations of building performance in earthquakes.  I believe the '97 UBC
now makes some statements in the beginning of Section 1626 to make this
issue a little clearer, but of course most cities are not using it yet.
Pretty interesting.

Kent Estes, S.E.


	----------
	From:  Harris3803[SMTP:Harris3803(--nospam--at)aol.com]
	Sent:  Tuesday, May 19, 1998 7:51 PM
	To:  seaoc(--nospam--at)seaoc.org
	Subject:  Soil report seismic acceleration minimums??

	     A fellow engineer called me today to ask what others are doing
now that
	soil reports have expanded into discussing seismic accelerations for
design.
	     This case is a one story wood frame office in Piru. The soil
stated a
	maximum near fault earthquake of magnitude 7 with an acceleration of
1.3G . 
	     My experience plan checking other projects of this type is
nearly all (
	all . ? ) design for '94 UBC Z= .4G and ignore the soil report . The
building
	department can only enforce the code with local amendments so this
will get a
	permit.
	    The '97 code will require a 30% increase since it is a near
source fault
	type b area. 
	     The engineer wanted my opinion but i was not sure of my advice
: Design
	to the '97 code requirements since for this type of structure, a 30%
increase
	is not a significant cost increase and one story wood frame to L.A.
city
	standards ( Ventura Co requires this ) should do well anyway. 
	     Is there a way to equate an acceleration from a soil report to
a design
	force for wood frame?
	     I would appreciate any opinions on how you would ( will ? )
handle
	similar situations.
	     Thanks in advance.

	     Tom Harris , SE
	     Thousand Oaks, CA

	    P.S. Should there be a surcharge for providing '97 code design
now (
	optional ) since it takes more time?