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RE: Soil report seismic acceleration minimums??[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaoc(--nospam--at)seaoc.org'" <seaoc(--nospam--at)seaoc.org>
- Subject: RE: Soil report seismic acceleration minimums??
- From: "Estes, Kent R." <kent_estes(--nospam--at)wdi.disney.com>
- Date: Thu, 21 May 1998 13:55:28 -0700
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?
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