A question on forces on a tank (joining two)

[Anonymous]

Hehehe you're assuming I want to use that saved money on a high tech alternative See when I save money, I want to keep that money saved

 

[Anonymous]

Mike, seven is right. Contact Mikeo or Al G Blenny on the BAR site, or RC. They have a name of a cheap fabricator that has done many local welded stands.

 

[Anonymous]

Cough cough, gag

(blowing the dust off my Formulas for stress and strains fifth edition (Roark and Young))

Refrenc page 389 table 26 case 7

A flat plate with two sides simply supported, the bottom rigidly supported, and the top unsuppported. Simply supported means the end can rotate slightly but does not "bow" outward. Whereas rigidly suported means the edge can not bow or rotate. Further, there is a uniformly increasing load from the top to the bottom. The max stress is (beta)qb^2/t^2. Where b is the height, q is the pressure which is density times height. t is the thickness, and beta is the ratio of the width to the height. That stress is located at the center bottom edge.

Assuming the tanks are about twice as long as they are tall beta on each tank is 2. after assembling the two together beta increases to 4. Betta for 2 is .667 for 3 is .866 and not listed for 4.

Everything else is constant except the width of the tanks So from 2-3 the stress increases .866/.667=1.29. Not as much as I first expected. A 50% increase in width only resulted in a 29% increase in stress. So doubling the width may mean a 50% or so increase. A simliar increase is predicted in the force in the silicon joint holding the glass to the bottom of the tank.

But that still is very significant. After all the glass thickness has not increased for the additional stress. Nor has the area for the glue joint on the bottom either. Plus the stress is now at the worse possible location. Right at the bottom joint where the two tanks meet.

To be on the safe side it would be better to place the tanks together with all the glass still intact.

 

[Anonymous]

To be on the safe side it would be better to place the tanks together with all the glass still intact.

Say what? So basically just have two tanks side by side with no missing panels? If so what would be the point of putting two tanks together?

 

[Anonymous]

PLB, thanx for looking up the Roark & Young reference.

The steel frame should still be a viable solution, all you need to find out is the thickness and shape for the steel tubing.

If you must put the tank end to end like what PLB suggested, you can use one of those fish highway... I meant aquaduct/siphon for it. I suggest you use the following design for best result:

You may want to save these images before they are deleted.

 

[Anonymous]

I think we are all on the same page and I did like dusting off my old roark's.

My 'gut feel' is that you either have to:


1) keep the tank ends in place.

2) add external structure to take the forces the ends would have taken.

3) use thicker glass in the longer tank

To maintain structural integrity.

what you should not do IMHO is just but the two panes together and expect a silicon bead to be sufficient.

 

[Anonymous]

I think the fish hiway would be not a good idea. In order to hold water, each tank would have to be sealed. Which means the maximum water pressure would be from the top water level at the top of the hiway to the bottom of the tank. Obviously the tanks were not designed for water pressure from that height.

 

[Anonymous]

PLB, I think you may want to verify the extra pressure with a siphon and see if I am wrong on this. It does not add more water pressure to the tank since all siphon is sealed. If the siphon is held up by a separate structure (that is, the siphon does not touch the tank directly), there is no detectable property for the existence of such structure in the system unless the siphon broke, or the water flow is strong.

Put it simply, if you put a static siphon (that is, siphon's water levels on both ends are the same, and there is no water flow between the containers), no matter how tall is the siphon, the water pressure is equal to the depth of the water depth in the container.

You can think of a static siphon as a long tube that is sealed on the top. See pressure diagram of a mercury barometer, for example.

 

[Anonymous]

ummm I know there's some nice debate going here, but I will NEVER go for the fish highway

 

[Anonymous]

PLB, I think you may want to verify the extra pressure with a siphon and see if I am wrong on this. It does not add more water pressure to the tank since all siphon is sealed. If the siphon is held up by a separate structure (that is, the siphon does not touch the tank directly), there is no detectable property for the existence of such structure in the system unless the siphon broke, or the water flow is strong.

Put it simply, if you put a static siphon (that is, siphon's water levels on both ends are the same, and there is no water flow between the containers), no matter how tall is the siphon, the water pressure is equal to the depth of the water depth in the container.

You can think of a static siphon as a long tube that is sealed on the top. See pressure diagram of a mercury barometer, for example.

The pressure is going to be the density of the water times the height of the water. Neglecting friction (ie a very large cross section syphon) that is going to be the pressure at the bottom of the syphons.

Therefore, regardless of the shape of the tank a 10' tank will have the same forces at the bottom if it is just single vertical column or a u shaped column. As from roarck above narrow flat plates require less force at the bottom center to resist that pressure. But the pressure on the plates are there still the same. But don't expect a 10' tall hiway to have the same forces as 1' tall 10g tank. The water pressure at the bottom is still 10'.

And I agree that I personally would never want one of these things.

 

[Anonymous]

I agree with your analysis if the siphon is broken. In a regular siphon (no air inside) that is supported by a separate structure, it give no additional pressure or weight to the water its ends are in. Again, take a look at a pressure diagram of a mercury barometer, and that should convince you that.

 

[Anonymous]

ummm I know there's some nice debate going here, but I will NEVER go for the fish highway

There is no debate here. But from past experiences, I guess people can debate over rather 9+4 is a prime number.

 

[Anonymous]

I agree with your analysis if the siphon is broken. In a regular siphon (no air inside) that is supported by a separate structure, it give no additional pressure or weight to the water its ends are in. Again, take a look at a pressure diagram of a mercury barometer, and that should convince you that.

And i agree with you also.

If you suck out the air there no longer is atmospheric pressure on the top or the water. So the atmospheric pressure on the sides of the siphon help support the water. and if the syphon is tall and skinny more and more of the pressure forces are reacted by the siphon joints/walls with less being reacted at the bottom joint. And with no bottom joint none is reacted out at the bottom. So you should be able to get by with thinner siphon material.

Hopefully the tanks at the bottom could handle the water if siphon is broken.

 

[Anonymous]

No matter what shape the siphon/water highway is, there is no additonal pressure on the tank if it is supported by a different structure.

Glad that this "debate" is over.... or it is not? :? :lol:

 

[Anonymous]

We both agree. A siphon has forces in the tube not the tank.

And thanks for this "debate". I really enjoy thinking through my ignorance.

It's the way I learn.

thanks.