Re: earthquakes and tank supports

[Sarah LeGates <slegates@yahoo.com>]

Hello all,
having experienced a couple of small tremors in my new home town in
the East Bay, I've been giving this issue some thought indeed. 
Someone with a little more experience in physics can correct me if I
get this wrong, but I would imagine the two big forces we're
concerned with are inertia and friction, and how our tanks respond to
the energy input from the quake.  The short version is that inertia
is what makes the water slosh, and friction keeps the tank on the
stand and the stand in one place on the floor.  Someone mentioned in
an earlier post that one of their tanks moved nearly 2" on its stand
during a quake, which means that the force of the quake was
sufficient to overcome the friction between tank and stand and shift
the tank by that much.  I know that under normal circumstances I
cannot shift any of my tanks when they are full, so you can imagine
how much force was being applied to that tank and stand during the
quake.  If your tank and stand are both fixed to the wall, the only
way the force of the quake can be expressed is through water motion,
and as mike mentioned that force might burst the seams of the tank,
or if nothing else there will be a lot more sloshed water than if the
stand alone is anchored.  It seems that anchoring the stand is done
with an eye towards keeping the stand and tank from toppling, since
the principle of dissipating energy via tank movement would also
apply to stand movement(though certainly you'll lose much more water
if the tank falls over!).  It was either posted here or on the Krib
that someone had installed "bumpers" on their stands to keep the tank
itself from shifting all the way off, which I think is probably a
better choice than anchoring the tank to the wall with strapping. 
So, do any real physicists out there want to add to my science?  It's
been a while since I took physics...

Cheers from the fault zone,

Sarah LeGates

--- Mike & Diane Wise <apistowise@bewellnet.com> wrote:
> Daniel,
> 
> If the tank were firmly anchored, I'd worry about the sides
> bursting due to the
> pressure of
> "sloshing" water. If the tank can move, "give" a little, I'd expect
> there to be
> less stress on the glass. Just a thought. Hmm. Aquarium air bag
> (like in
> automobiles)?? I wonder if there's a market there? :-)
> 

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