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Re: earthquakes and tank supports


What the situation calls for is a structural engineer. I'm an architect,
which is not quite the same thing, but I know that there are a few solutions
used in buildings to maximize life safety and minimize damage in the event
of seismic activity (a.k.a. lateral forces and uplift).

    The ideal solution for aquaria, it seems to me, should include some type
of dampening of forces as they transmit themselves thru the building. I
don't know exactly how this could be accomplished with a tank stand, but at
the building scale it is sometimes done with large steel springs and
pneumatics. This is used only in steel and concrete construction, as far as
I know.

    Here's an over-simplified explanation (this is actually fairly new
technology and hasn't become standard in construction yet): A building would
have two steel frames. One is rigid, to resist lateral forces - it's
basically a vertical truss of steel columns, beams, and diagonal members,
braced to the ground. The other is more flexible - columns and beams (no
diagonals) which support concrete floors and roof, and the connections
between the members are allowed to 'give' a little, i.e. no moment
resistance. The walls sit on the concrete and are nonstructural. At various
points between the two frames, you put steel disk springs and large
pneumatic shock absorbers. When lateral forces transmit from the ground
through the rigid steel frame, the rigid frame moves but the force is
dampened before being transmitted to the more flexible frame, so the
periodicity of the seismic activity is reduced. Thus the building doesn't
move so much, giving you less damage and more safety.

    I imagine a system like this could be developed for tank stands. Perhaps
you make a rigid framework - steel or wood - and anchor it firmly to the
floor and wall. Then you 'float' a shelf on top of the framework, so that
there is minimal friction between it and the frame. Leave space at the edges
and put...oh, say, neoprene padding between the shelf and the vertical
members of the frame. Attach the tank firmly to the shelf somehow.

    That might help mitigate the shock of lateral forces.

    The only other force you need to be concerned with is uplift, because
earthquakes move in both horizontal and vertical directions. The only thing
you can do about that is make sure the shelf and tank are restrained from
moving upwards somehow - perhaps a piece of wood or steel that runs over the
top surface of the shelf, attached only to the framework. This would allow
the shelf to move in the horizontal direction but not in the vertical.

    Unfortunately, seismic engineering hasn't come up with a really
effective way of dealing with uplift, for minimizing damage to buildings. We
can do a pretty good job with lateral forces, and we can deal with life
safety issues in terms of uplift, but damage is just going to happen when
you have one of those rolling up-and-down type of earthquakes. Just keep
things restrained, i.e. tank lids, filters, etc.

    Hope this helps!


ps welcome to the bay area!

</end delurk>

-----Original Message-----
From: Sarah LeGates <slegates@yahoo.com>
To: apisto@listbox.com <apisto@listbox.com>
Date: Sunday, March 04, 2001 11:14 AM
Subject: Re: earthquakes and tank supports

>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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