Aquarium Engineering Design - Joint Strength

[Elemeno]

I would like to build a 60 gallon rimless cube (24"x24"x24") aquarium from 1/2" glass.

My question is about the strength of the resulting aquarium.

Which method produces the strongest aquarium:

1.) The sides are glued on top of the bottom.
2.) The bottom is glued inside of the sides. (i.e. The sides are glued along the edges of the bottom.)

If there's a better way or it doesn't really matter, I'd be interested in knowing.

Any help in this matter is greatly appreciated.

(Apologies if this has been covered, an internet search has left me empty handed.)

 

[sleepydoc]

Uncle's the best person to answer this, but in general it doesn't matter.

As to which is technically stronger, you can't say without knowing the characteristics of the particular silicone you're using.

 

[Elemeno]

After performing the various force/pressure calculations and comparing the results with the tensile strength of the silicone used in bonding the edges... it may matter an insignificant amount due to the tear vs tensile strength of the silicone used. Using the RTV108 stats - either method would work.

The only difference I've been able to ascertain is that the weight of the side walls may be better supported by the aquarium stand rather than the silicone and glass bottom thus eliminating tearing and compression forces acting on the joint and using the full tensile strength of the silicone to pull the wall in.

Bottom inside appears to be a safe bet, but for smallish tanks and/or tanks with braces it wouldn't matter to a significant degree, provided the silicone used had high tear and tensile strength.

 

[uncleof6]

A very lucid, literate evaluation. However, neither of the properties you evaluated using calculations, have anything to do with holding two panes of glass together. You merely anylized the physical properties of the silicone in reference to itself. E.G how much force is required to seperate the silicone from itself. Rip it in half (tear,) stretch it (tensile) till it breaks, etc.) We use the RTV100 series, or SCS1200 series, due to their high adhesive strength.

What holds the panes of glass together is the adhesive strength, (related to the peel strength,) silicones weakest property, and is always the weakest. You can have a tensile strength of 1000psi, but if the adhesive strength is only 1lbs/in, you will have glass all over the place. This is why the RTV100 series will hold a tank together, and HD garbage consumer grade silicone won't. (Except for nanos on down, and that is pushing it.) Dow Corning 999A, or 735 are better choices for small tanks.

This topic has been round and round, usually very literate and lucid, however irrelevant as it is. What makes the difference on the seams is the WIDTH of the seam, not the configuration of the tank: the wider the seam the stronger the bond between panels will be. When tanks self destruct at the seams, due to whatever cause, the silicone does not rupture, rather it pulls away from the glass. Adhesive strength: the weakest link in the chain.

Somewhat related to this is the thickness of the seam. The thickness should generally be ~ 1.5mm (1/16") for most tanks that amatuers should be building. This is a bit subjective however, and experience is involved. Larger tanks are best left to those that know what they are doing...

 

[Elemeno]

Eventually the adhesive strength of the bond will exceed
the cohesive strength of the silicone rubber sealant itself.

Under bond strength development:

http://www.momentive.com/products/showtechnicaldatasheet.aspx?id=10289

Thank you for the additional information.

 

[NanoReefWanabe]

A very lucid, literate evaluation. However, neither of the properties you evaluated using calculations, have anything to do with holding two panes of glass together. You merely anylized the physical properties of the silicone in reference to itself. E.G how much force is required to seperate the silicone from itself. Rip it in half (tear,) stretch it (tensile) till it breaks, etc.) We use the RTV100 series, or SCS1200 series, due to their high adhesive strength.

What holds the panes of glass together is the adhesive strength, (related to the peel strength,) silicones weakest property, and is always the weakest. You can have a tensile strength of 1000psi, but if the adhesive strength is only 1lbs/in, you will have glass all over the place. This is why the RTV100 series will hold a tank together, and HD garbage consumer grade silicone won't. (Except for nanos on down, and that is pushing it.) Dow Corning 999A, or 735 are better choices for small tanks.

This topic has been round and round, usually very literate and lucid, however irrelevant as it is. What makes the difference on the seams is the WIDTH of the seam, not the configuration of the tank: the wider the seam the stronger the bond between panels will be. When tanks self destruct at the seams, due to whatever cause, the silicone does not rupture, rather it pulls away from the glass. Adhesive strength: the weakest link in the chain.

Somewhat related to this is the thickness of the seam. The thickness should generally be ~ 1.5mm (1/16") for most tanks that amatuers should be building. This is a bit subjective however, and experience is involved. Larger tanks are best left to those that know what they are doing...

That said panes around the bottom make the most sense, as the bottom pane of glass is generally 1.5 times thicker then the sides"¦hence 12mm sides would usually have a 17mm or so bottom"¦even if you use the same thickness for the bottom then you would normally euro brace the bottom making it a 24mm wide seam"¦so as per uncles statements, glass around the bottom is considerably better

 

[Gorgok]

Panes around the bottom is probably a harder build to do right though, unless you are sure the surface you build on is absolutely flat. Getting 4 independent edges coplanar would be annoying if it wasn't.

 

[uncleof6]

That said panes around the bottom make the most sense, as the bottom pane of glass is generally 1.5 times thicker then the sides"¦hence 12mm sides would usually have a 17mm or so bottom"¦even if you use the same thickness for the bottom then you would normally euro brace the bottom making it a 24mm wide seam"¦so as per uncles statements, glass around the bottom is considerably better

Absolutely correct. However, not all inclusive. I am not arguing either/or. There are a couple ways to go about this.

I build sides around bottom, it is easier than doing sides on top of bottom, as you don't need to use spacers to keep heavy panes of glass from squishing out too much silicone, and you don't have heavy glass panels sliding away from you when it touches the silicone. That said, if you use 12mm bottom, 12mm sides, sides on top of bottom, using a 12mm bottom euro (necessary in this case, as thicker bottom pane won't add anything,) what is the width of the bottom seam? With a thicker bottom panel than sides, generally the bottom euro is not going to be necessary, if you know how to calculate for a rimless tank. Online calculators figure rimmed only, and don't allow for rimless, despite what the blurb says about it. You will always find a blurb stating: "Assumes a full metal rim." But let's face it: a bottom euro certainly won't hurt anything.

If you are building a full-floated bottom tank, (bottom up inside the sides by 1/4" or so, though you get the advantage of being able to support it like a rimmed tank, you must use a thicker bottom panel, and a bottom euro is a good idea as well.

 

[uncleof6]

Panes around the bottom is probably a harder build to do right though, unless you are sure the surface you build on is absolutely flat. Getting 4 independent edges coplanar would be annoying if it wasn't.

Should not be building tanks of any type or configuration on a surface that is not dead flat...that is just good common sense...there are very few reasons a tank will hold together, and hold together over the long haul. There are a myriad of reasons why they won't last...

 

[mkj]

I noticed that most recommend euro braces to go on top of pans. Is it ok to run the euro brace on the inside edge, or is this weaker?