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- Subject: [SEAOC] Re: [SEAOC] Buried or partially buried structures
- From: smthengr(--nospam--at)sirius.com (Jeff Smith)
- Date: Tue, 11 Jun 1996 10:50:42 -0800
I am also very interested in what other engineers are doing regarding this subject. Latley I have been taking a "poll" when I get the chance to talk to different geotechnical engineers. What I have found is that the UBC only makes a vague reference to required seismic forces due to soil loads and as far as I can tell there is not actual prescribed code load. Seed and Whitman(1970) and ATC(1979) addresses this issue and refers to it as a seismic increment. The loads can range from a rectangular distribution of 10-40H psf *plus* EFP. I have seen cases where the seismic increment will dominate the wall design. Add traffic surcharge and maybe a wall Fp and you will end up with quite a bunker. Some soils engineers will provide a seismic increment, others will only provide it if requested and some do not beleive it exists. The seismic increment was apparently tested using shake table studies. I have also heard that the seismic increment may not be appropriate for walls less than 10 feet unless the walls are finish spaces with very little tolerance for deflection. I beleive that within the last 5-10 years, it is more common that structures with two to or more story basements, in Zone IV are designed using a seismic increment. Do other engineers agree? What do you think? Any Geotechnical engineers have any comments? >To All: >I am wondering what the standard practice is for adding seismic loads from >soil to buried or partially buried structures? In the past, we have added >such loading when doing DSA and OSHPD work per Title 24. As far as I can >tell, the new 1994 UBC makes no mention of it. The 1995 California Code >requires that it be considered if there is more than a 6 foot differential in >soil height on opposite sides of the structure. >I am looking for some feedback as far as what other Engineers are doing, or >what is "usual and customery" for practicing consulting structural engineers >to do in their designs. >To be specific (if this will help), we are doing a design of some man made >"wine caves" for a local Santa Barbara winery. This is an area where the >public will go and taste wine and get tipsy before they go on to the next >winery down the road :) >Some of the cave is completely buried on both sides, some of it is buried >only on one side, and everything inbetween. So what do you say, are we being >too conservative if we throw in some soil loading? It does make a >substantail difference in our desgin, and will cost the Owner significantly >more if we do it. I obviously don't want this thing to come down in an >earthquake, but at the same time, I don't want to spend the Owner's money >needlessly. > >Lynn > >... Regards, Jeff Smith. S.E. phone: (415) 543-8651 fax: (415) 543-8679 email: smthengr(--nospam--at)sirius.com Smith Engineering 27 South Park San Francisco, CA 94107 ...
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