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RE: EQ forces- Retaining Wall

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I don't think I would assume a filter plant is a non-building structure. You
need to assume something for seismic soil design, but treating a backfilled
wall as a retaining wall may or may not be appropriate, since the walls of
backfilled treatment plant structures often have a lot of top restraint,
either from floors or intersecting walkways, or from their shape in the case
of circular tanks. 

I would recommend that you assume at-rest soil pressures for the design of
buried structures like this, unless your geotechnical engineer feels
comfortable telling you otherwise. Monanobe-Okabe methods assume active
earth pressures and may understate the seismic soil pressure. The AASHTO
Standard Specifications for bridge design recommend that you use a
significantly higher seismic factor (1.5 x seismic coefficient for
non-yielding walls compared to .5 x seismic coefficient for free-standing
retaining walls) when using the M-O method. 

Use of Wood's method for seismic pressures on non-yielding walls is another
alternative. For deep structures, the pressures predicted by these methods
are pretty high. The UBC has nothing in it that will help you define seismic
soil pressures. You should be getting recommendations from your geotechnical
engineer for this kind of thing.


-----Original Message-----
From: Lakhani, Sid [mailto:slakhani(--nospam--at)ebmud.com]
Sent: Tuesday, January 23, 2001 7:02 PM
To: 'seaint(--nospam--at)seaint.org'
Subject: EQ forces- Retaining Wall


Is retaining wall a non building structure(NBS) ?.  Is it mentioned any
where in UBC-97 ?

I am designing a filter plant structure.  For soil seismic force I am using
a formula with  R value of 2.7.  So It appears that I can assume  the
retaining wall as NBS

I would like to know if there is a standard practice to assume the retaining
wall as a NBS.  Or should I determine the EQ forces per UBC-97 section
1632.2 for element  Also please let me know a reference which has design of
retaining wall for EQ forces.    

Thanks in advance.    Sid LaKhani