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# Re: Seismic Design of Nitrogen Storage Tank

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Seismic Design of Nitrogen Storage Tank
• From: <seaint04(--nospam--at)lewisengineering.com>
• Date: Tue, 04 Nov 2008 15:01:59 -0700

```Steve,

Thanks for the response.

I think I found that I can use ASCE 7-05 15.7.8 for my design.  I believe
the exception of 15.7.13.1 will let me do this for a liquid nitrogen tank.
What I'm wondering is just how to get the Impulsive force (tank) and the
convective force (sloshing) for my system.  I reviewed the example problems
of FEMA 450 and they seem to refer to API 652, 650 and AWWA D100 at just
the critical time of explaining something.  Unfortunately I do not have
these publications.

I seem to have one hangup that I was hoping some Standard would solve.
That is to calculate the fundamental period of the tank structure.  To
calculate the impulsive force I need to know the fundamental period of the
tank.  The only information I have of the tank are the dimensions.  I'm
researching how I can calculate the fundamental period of the tank vessel.
I have a copy of '2006 IBC Structural/Seismic Design Manual'.  Example 53
gives an equation of T=7.65x10^-6*(L/D)^2*(wd/t)^0.5.  It doesn't say where
this equation came from some I'm not sure it is valid in my case.

To calculate the convective force I again need to know the fundamental
period of the tank.  Any insight on this would be appreciated.

Rich

On Tue, 4 Nov 2008 10:23:33 -0800, "Steve Gordin"
<sgordin(--nospam--at)sgeconsulting.com> wrote:
> 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 --

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