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RE: Soil report seismic acceleration minimums??

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Just out of interest where did he/she get the data from, and exactly what
did they give you.

John Nichols

At 13:55 21/05/98 -0700, you wrote:
>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)]
>	Sent:  Tuesday, May 19, 1998 7:51 PM
>	To:  seaoc(--nospam--at)
>	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
>	     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
>	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%
>	is not a significant cost increase and one story wood frame to L.A.
>	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 ? )
>	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?