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RE: Seismic mass

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If you are designing a daylight basement, with the cmu wall retaining a slope on one side only, I would probably analyze that as a two story structure.  If it is a full basement below grade, then I would run the lateral calcs on the one story portion of the house only – and then analyze the basement retaining walls separately, using whatever EFP the geotech gave me.  You need a geotech engineer to give you lateral seismic soil surcharge loads on retaining walls per the IBC.


~~ Eli ~~


-----Original Message-----
From: Jnapd(--nospam--at) [mailto:Jnapd(--nospam--at)]
Sent: Tuesday, February 07, 2006 10:55 AM
To: seaint(--nospam--at)
Subject: Re: Seismic mass


Paul and others:


Another twist to that question..........I have been asked to design a retaining wall for a house that is in the FEMA flood plane of Riverside County.  The county has a spec sheet they give out.


6'-0" retained height,    8" cmu  #4's @ 16oc at center of wall,  footing 12" wide 36" deep

4" slab on grade at top of wall,  house sits on top of this.

EFP 30psf;  1500psf soil Bearing;  Passive 250pcf;  soil 115pcf;   solid grout no inspection.

County claims it is only good 10km from Type B fault)


I cannot get it to calc out as restrained let along cantilevered.


My question is doing a lateral on the project would you do it as two story and use only the cmu wall weight in the analysis or.........


Do the house calc separately and at as load at top of rigid floor slab.


Would you at some weight for the dirt in the analysis for the Retained structure ??




Joe Venuti
Johnson & Nielsen Associates
Palm Springs, CA