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RE: Free Standing Concrete Wall Seismic Design

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Tom,
 
For free standing walls, I've used Formula 15.4-5 although it is probably not technically a "rigid" structure. My logic has been, (other than using a "simple" formula for the siesmic forces), that under the old UBC codes in a high seismic zone, (4), the seismic force was allowed to be 0.2 x dead load. Using an Sds of about 1.4, (common in my area), you get a strenght seimic force of about 0.42 load, or 0.3 ASD. I think using formula 13.3-1 gives too high a seimic force, (unless that is what you want), for a cantilevered non-building element, (unless you just use formula 13.3-3 which is the same as 15.4-5).
 
Regards,
 
Larry Huaer, S.E.
 

To: seaint(--nospam--at)seaint.org
Subject: Free Standing Concrete Wall Seismic Design
From: Tom.Hunt(--nospam--at)fluor.com
Date: Mon, 8 Mar 2010 14:21:23 -0800


I think this may have been discussed previously but I could not find it.  I have a 14 foot high free standing concrete wall that looks like a typical retaining wall with 2 feet of soil on both sides (i.e. the wall sticks out 12 feet above grade).  The only purpose of the wall is to provide secondary containment if a large steel storm water tank inside the walled area fails (i.e. a once in life time event).  From a seismic standpoint (i.e. neglecting any water and assuming concrete dead load only) would the seismic loads from ASCE 7-05 be determined from Chapter 13 using Fp or from Chapter 15 using V.  If considering Chapter 13, I would assume an ap of 1.0 and an Rp of 2.5 for an exterior nonstructural cantilever wall.  If from Chapter 15, I would assume an R value of 3 for all other steel and reinforced concrete distributed mass cantilever structures.  Any comments?

Thanks,

Thomas Hunt, S.E.
Fluor
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