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Re: Seismic Design of Nitrogen Storage Tank

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Rich,
 
There is no magic here, the "industry standard" is to apply ASCE7 Chapter 13 and 15.  It should be noted that, in spite of the presumed engineering simplicity of the problem, there are several issues in this design that are usually missed, including - but not limited to: 1) "diagonal" direction of the lateral force; 2) punching shear on thinner pads; 3) asymmetric location of three legs on the pad (while the tank may be centered on the pad, the moment arm for concrete design is longer in one direction). 
 
Also, the pads for this type of installations tend to accommodate more equipment than just the tanks (for example, vaporizers that may become quite heavy).  In these instances, a beam-on-elastic foundation approach may be suggested for more accurate evaluation of moments (watch the pad uplift, though - soil does not provide resistance in this direction).  In some complex cases I use the FEA for the pad as supported by the one-way springs.
 
HTH,
 
V. Steve Gordin, SE
Irvine CA
 
 
 
 
 
    
  
 
 
----- Original Message -----
Sent: Tuesday, November 04, 2008 09:03
Subject: Seismic Design of Nitrogen Storage Tank

I need to design a foundation for a nitrogen storage tank.  The tank is 8
ft diameter x 37 feet tall.  It is supported on 3 legs, about 2 feet off of
the base.  I wondering which guidelines are used for the seismic force
analysis.  FEMA 450 (2003) section 14.4.7.12 that refrigerated liquids are
beyond the scope of the standard and references commentary section
14.1.2.2.  In the commentary they list a bunch of standards but none seem
to apply to refrigerated pressure vessels.  Can someone point me in the
right direction of which standard to use to perform a seismic analysis for
this type of tank?

Thanks.

Rich



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