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Re: Fundamental Frequency of Tall Steel Tank

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3 ideas:
wouldn't it work to take your cross-sectional inertia, and use L^3/3EI
type factor (for cantilever) for K, and then use lumped mass, and then
sqrt(k/m)?  I think this should be fine, no?

or find a stiffness for your support configuration, applying unit
loads at particular locations ...  it is not a simple equation, it
depends on your support points and what kind of wiggling its going to
do, how many mass lumps you will consider.  if you want a more
sophisticated approach, model it as a cantiliver with the inertia and
E that you have (you don't need to get so sophisticated to model the
tube), then run a dynamic analysis, and find your frequencies.

you could just take a default value, and see if a gust factor is
really going to affect your overall system.
refugio rochin

On 10/6/06, M. David Finley, P.E., P.A. <davidfinley(--nospam--at)> wrote:

I'm doing some preliminary sizing for the foundations for some tall
cylindrical steel tanks - 8'-0" diameter x 66'-0" high.  They will be in a
low seismic area, so wind loading is my concern right now.

I need to estimate the fundamental frequency of the tank in order to
determine the Gust Factor per ASCE 7.  Can someone point me to a good
reference?  Is there a reasonably conservative value I can assume for this
preliminary work?

Since I am just considering wind at this point, the empty tank will control
and therefore I don't need to consider the added effects of the liquid
contents in determining the fundamental frequency, right?


David Finley
M. David Finley, P.E., P.A.
2086 SW Main Boulevard - Suite 111
Lake City, FL  32025

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