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[SEAOC] Re: [SEAOC] Buried or partially buried structures

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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 

Jeff Smith. S.E.
phone: (415) 543-8651
fax: (415) 543-8679
email: smthengr(--nospam--at)

Smith Engineering
27 South Park
San Francisco, CA 94107