Re: Exploding glass, unven floors, 90 gallons

[Bill Wichers <billw at waveform_net>]

I quote more than one post here...

> I was refering to inserting a piece of foam or cork which will cover
> the
> entire bottom of the tank.

Very few tanks I have seen except for DIY tanks are supported evenly across
the entire tank bottom. Almost all commercially made tanks (except for
acrylic) are supported only by a rim of less than 1" wide around the outer
perimeter. In a situation like this, the pressures placed on the foam will
be extreme. The foam, however, will compress more in the more loaded places
and less in the less loaded places, thus most of the tanks weight will
still be supported in a few places. Even in those places where the foam is
carrying some of the load, I still don't think it will be enough to be of
significant benefit. There is also the other concern of aging of the foam.
Most plastic foam materials will not remain "spongy" forever. As a result,
the foam will gradually carry less and less load in the areas you are
trying to "even out" until you're back to nearly where you were before the
foam.

>will hold the tank?  I would think it better to rest the weight at the
>rim where the veritcal panels lend rigidity.  I'm no engineer, though. 
>I'll defer to some hard data on weights and structures.  Maybe I can
>get one of the bridge engineers at my agency to give this some thought.

I agree with Scott here. I'll actually go a bit further thinking that
supporting the center panel may actually be *bad* since you will be
pressing it up against the rim and placing making it bow up in the center.
This will add additional stresses to the tank that the tank was not
designed to support.

It would be interesting to hear the input of a structural engineer on this.

> This way the pressure will be distributed
> evenly over the entire bottom.  The foam will be compressed to
> comform to
> the uneven surface.  Without the foam, if there is a bump on the
> surface
> which the tank sit on, tremendous pressure & stress can be
> concentrated on
> that bump. 

This will still result in most of the force resting on the rim. The more a
tank part protrudes from the average level of the base, the more load it
will carry. Bumps are a different matter, but most are likely to be easily
removed before placing the tank on the stand.

>Speaking for myself and not Bill, I agree about the bumps but not that
>foam will help.  Maybe a very small "corn," but those should be
>removed, imo, rather than foamed over.  It won't do enough of what you
>want, it won't distribute enough weight, it won't provide enough
>pressure between the tank and the stand to "eliminate" or fill a gap.

Sounds like I pretty much agree with you, so you've said the same kinds of
stuff :-)

The only thing I could see doing to even out a bad stand, and I still think
a good stand is better than a "band-aid" over a bad stand, would be a rigid
support. Maybe a layer of some material like liquid nails that hardens
could be used since after hardening the tank could be filled, and there
would be a rigid support in all the gaps. It would probably be easier to
just put a new top on a stand though. A piece of pine plywood would work
well with the pine being soft enough smooth small differences out from
pressure, but hard enough to offer some real support.

     -Bill

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Waveform Technology
UNIX Systems Administrator