Rimless Aquarium Help? Yes, I used Google. Head Really Hurts.

[Bill_68]

Hello All,

 

I found some nice glass. It is just over 3/8" thick. It is not tempered. I got it from a store that was selling off fixtures.

 

The panels are 16" x 38" x just over 3/8" thick. I bought ten of them for 20$. SCORE! They are beautifully beveled on the edges.

 

I was thinking FRAG TANK! 38" x 38 3/4" x 16"

 

So, Do I need bracing? http://www.theaquatools.com/building-your-aquarium says "No." It does not specify glass kind and I am a bit concerned.

 

Also, how thick does the bottom need to be? I am a bit concerned about safety here, since it doesn't have a frame. I have heard of people using Plywood painted with epoxy resin? Seemed odd to me.

 

Ideas anyone?

 

Bill

 

 

 

 

[GHill762]

sorry, I'm no engineer.. lol.. can't help with yes or no.. but if you decide to put a brace on it consider a euro brace.. it'll help you keep that clean rimless look.

[Mr. Microscope]

3/8 might be okay for that height without bracing. Check out the GARF website:

http://www.garf.org/tank/buildtank.asp

 

For those dimensions, it recommends 1/4 glass with some braces.

[hey]

http://www.fnzas.org.nz/?page_id=1635

 

use a safety factor of 3.8 as its the industry standard... could go higher if you want. Silicone is going to be your weak point make sure to use momentive rtv 103 or 108 its pretty much the only one worth using. The calculator is for a rimmed tank but the rim on a tank unless braced in the middle is only for keeping the silicone in place/ease of assembly. The website has some very useful info on glass strength if you are interested.

 

With those measurements I am seeing it requires 6.5 mm glass and at that thickness would bow out .318mm.

 

If you use glass at 9.525mm or 3/8th you have a safety factor of 8.1099 and it will bow out .109 inches.

[Bill_68]

Thanks for the links. I thought it was odd that one of the sites showed the bottom panel as being the length less the thickness of the glass x2.

 

This is my first rimless. Doesn't the bottom equal the external size in an aquarium? Do you. Have a factor for silicone thickness that you add to that dimension.

 

For example, if your sides are 38 inches, the bottom should be 38 1/8 x 38 1/8 to allow for silicone bead of 1/16" or so?

 

Bill

 

 

[hey]

the bottom pane of glass is shorter in width and length than the width and length of the aquarium as the side panes sit beside the bottom and not on top of it. Silicone thickness is negligible on the thickness you wont get much of a difference in the dimensions.

[nibor]

3/8 is fine for your build.

 

 

When building rimless tanks, just look at what the commercial builders like Ada and Mr Aqua do for reference. You only need to consider the longest side. (Compare with an ADA 90P or Mr Aqua 48G).

 

The glass measures a little over 3/8 because of manufacturing standards/tolerances. 3/8 inch glass is the same as 10mm glass and can vary between about 9mm and 10.3mm in thickness and still conform. Better quality glass will have less variation. You can compare tanks advertised as being made from 10mm to 3/8, it is the same.

 

 

These calculators are wrongly used time after time after time.

 

The calculator linked to in the OP is based on the same mathematics as the one hey linked to. It assumes the glass is supported on all four sides, ie the aquarium is braced or framed. The mathematics are not the same for a rimless aquarium as the glass is supported on only three sides.

 

+1 for using an adhesive silicone like RTV103/8, not a silicone sealant like GE1.

 

-1 for the rim doing nothing unless braced on the middle. If this was true, nobody would bother euro bracing. The brace is perpendicular to the bending stress in the aquarium side and is very stiff, it deflects very little. The top edge of the aquarium is supported by the adhesive bond to the brace, the fourth side of support for the calculator.

 

Silicone thickness will be about 1/16 inch. Like hey said, negligible. Glass cutters will not work to that small a tolerance anyway. You would need to have the bottom piece ground to size to perfectly match. Only the very best tanks are made with such precision.

 

 

The thickness of the bottom depends on how you build and support the tank.

 

Build sides on top of the bottom and support the tank across the whole base on a stand with a rigid top that bends very little and you can use 3/8 or even 1/4 inch. If building sides around the bottom and only supporting the tank on the edges, you can use the calculations at fnzas to work it out (3/4 inch for a decent safety factor).

[hey]

3/8 is fine for your build.

 

 

When building rimless tanks, just look at what the commercial builders like Ada and Mr Aqua do for reference. You only need to consider the longest side. (Compare with an ADA 90P or Mr Aqua 48G).

 

The glass measures a little over 3/8 because of manufacturing standards/tolerances. 3/8 inch glass is the same as 10mm glass and can vary between about 9mm and 10.3mm in thickness and still conform. Better quality glass will have less variation. You can compare tanks advertised as being made from 10mm to 3/8, it is the same.

 

 

These calculators are wrongly used time after time after time.

 

The calculator linked to in the OP is based on the same mathematics as the one hey linked to. It assumes the glass is supported on all four sides, ie the aquarium is braced or framed. The mathematics are not the same for a rimless aquarium as the glass is supported on only three sides.

 

+1 for using an adhesive silicone like RTV103/8, not a silicone sealant like GE1.

 

-1 for the rim doing nothing unless braced on the middle. If this was true, nobody would bother euro bracing. The brace is perpendicular to the bending stress in the aquarium side and is very stiff, it deflects very little. The top edge of the aquarium is supported by the adhesive bond to the brace, the fourth side of support for the calculator.

 

Silicone thickness will be about 1/16 inch. Like hey said, negligible. Glass cutters will not work to that small a tolerance anyway. You would need to have the bottom piece ground to size to perfectly match. Only the very best tanks are made with such precision.

 

 

The thickness of the bottom depends on how you build and support the tank.

 

Build sides on top of the bottom and support the tank across the whole base on a stand with a rigid top that bends very little and you can use 3/8 or even 1/4 inch. If building sides around the bottom and only supporting the tank on the edges, you can use the calculations at fnzas to work it out (3/4 inch for a decent safety factor).

 

Please read the calculations in the main website not just guessing that it is the wrong calculation. It shows the exact formula used in the calculator and not once is the bracing taken into account and it also states what bracing is for ( to aid the application or compression of the silicone) which is the weak point as it will break far before glass at that pressure will.

 

Euro bracing the edges is completely different than a plastic silicone compression brace. Again the glass strength is what the calculator is accounting for there is absolutely zero math included for bracing.

 

In regards to just using a manufacturers example of a rimless tank you can then identify their factor of safety using the calculator in reverse and figure out glass thickness required. ada and mr aqua come out at 5.69 so putting that in with the height and long side gives a required thickness of 7.98mm.

 

I must stand corrected at the industry standard of 3.8 being for their rimmed tanks as obviously both ada and mr aqua go with 5.69. Checked the 60p aswell for reference also comes to 5.69 safety factor.

 

Taken from fnzas.org:

 

Design Considerations:

The calculations that follow expect the glass to be supported around its perimeter on all four sides. The calculation is the same regardless of whether the perimeter join is in compression or tension. Typical all glass aquariums have all their joins in either tension or shear or both. This method of construction relies 100% on the strength of the silicone holding it together, and is also the weakest join type when using silicone. Steel frame aquariums have the silicone under compression. The silicone is not required to have any strength for this type of aquarium and serves only as a sealer and packer.

The thickness of the bottom glass is covered by the second set of calculations, but does not cover an aquarium which has a bottom glass that is well supported from below the aquarium in an even uniform manner. The surface must be very level. On very large aquariums this can be difficult to achieve and self-leveling filler may be needed between the polystyrene and the base. This should be applied just prior to fitting the aquarium to the base so that the aquarium’s weight levels out imperfections. Significant time must be allowed for the filler to fully cure before the aquarium is filled. If the bottom glass is only to be supported by all four edges then use the second set of calculations. The same thickness glass can be used on a uniformly supported bottom as well and this will significantly improve the safety factor. If the aquarium is to be supported from below in a uniform distributed manor, then the same thickness glass that is used for the largest side panel may be used. To do so requires the supporting base to support part of the load so therefore it must be VERY strong.

NOTE: The calculations only consider the water to the top edge of the glass. If the glass is a window below the surface then it is outside the scope of this article.

[nibor]

I am not guessing anything.

 

The critical sentence from fnzas.org is the one before the block you bolded:

 

The calculations that follow expect the glass to be supported around its perimeter on all four sides.

A rimless tank is only supported on three sides, the calculation is not the same.

 

You are right, bracing does not figure mathematically in the calculator. The engineer that created it assumes a perfect brace or frame to support the four sides with no movement for his calculation as stated in the sentence I quoted.

 

This calculator is not for rimless tanks.....

[hey]

I am not guessing anything.

 

The critical sentence from fnzas.org is the one before the block you bolded:

 

A rimless tank is only supported on three sides, the calculation is not the same.

 

You are right, bracing does not figure mathematically in the calculator. The engineer that created it assumes a perfect brace or frame to support the four sides with no movement for his calculation as stated in the sentence I quoted.

 

This calculator is not for rimless tanks.....

 

The 4 side silicone support on all 4 sides is not the same as a perfect brace. There is a very large difference in forces acting on silicone at the seams vs the forces acting on compressed silicone pushing against a steel frame. The bendable plastic/silicone is doing jack to keep the glass from deflecting.

 

Did a little more searching and found http://www.plantedtank.net/forums/showthread.php?t=57295 which uses the glass' strength alone. While the numbers are slightly different it shows at a 3.8 safety factor 6.77mm instead of the silicone braced tanks 6.5mm and deflection .31 mm vs the braceds .318mm.

 

All in all the difference is negligable unless a cross brace / euro brace is involved. I can't check to see what numbers were adjusted in it but it kept his 230g system together for 3 years prior to thread dying out.

 

best part of this calc is the ease in which you can input dimensions and just take a guess at a thickness and you can tell if you can trust your living room floor to it or not.

[Bill_68]

Thanks for all the dialogue. I plan on getting a stone top and making a base out of something strong. We will see what the stoners think. Might be able to get something cheap as a remnant if I don't care about color. It's really too bad how expensive good wood is these days. I tried laminating 3/4 ply together with adhesive and screws. It ended up like a potato chip and ended up in the dumpster.

 

I would think that 1/2 or1/4 inch foam sheet good would be fine for leveling out the bottom. Sheet rubber? Vinyl membrane? Will think and read some more on that. Sadly, not very pretty and would have to cover with something. Glass on stone bottom would have looked really spiffy.

 

I'm thinking 2x and oak veneer and trim for a base.

 

Anyhow, thanks again.

 

Bill

[nibor]

 

I tried laminating 3/4 ply together with adhesive and screws. It ended up like a potato chip and ended up in the dumpster.

 

You could take a flat piece of ply and reinforce it by gluing and screwing some cross members to the bottom running in both directions. Use glued halved joints where the braces cross.

 

 

If you use a second piece of ply across the bottom of the braces, the box structure will be very strong. You could make a support frame from square steel tube or other metal stock.

 

 

The 4 side silicone support on all 4 sides is not the same as a perfect brace. There is a very large difference in forces acting on silicone at the seams vs the forces acting on compressed silicone pushing against a steel frame. The bendable plastic/silicone is doing jack to keep the glass from deflecting.

 

Did a little more searching and found http://www.plantedtank.net/forums/showthread.php?t=57295 which uses the glass' strength alone. While the numbers are slightly different it shows at a 3.8 safety factor 6.77mm instead of the silicone braced tanks 6.5mm and deflection .31 mm vs the braceds .318mm.

 

All in all the difference is negligable unless a cross brace / euro brace is involved. I can't check to see what numbers were adjusted in it but it kept his 230g system together for 3 years prior to thread dying out.

 

best part of this calc is the ease in which you can input dimensions and just take a guess at a thickness and you can tell if you can trust your living room floor to it or not.

 

You are finding more posts made by people who do not understand the limitations of this calculator. These mathematics will not calculate deflections, safety factors or glass thickness for rimless tanks. Using what has worked for other people however is sensible, tried and tested.

 

 

All any of these calculators do is calculate the bending stresses and deflection for a simply supported rectangular glass plate. They are all based on the same mathematics first published to the aquarium world at fnzas (check out Help/About in Aquacalc). They are taken directly from a famous engineering text called "Roark's Formulas for Stress and Strain". If you look in the excel spreadsheet calculator he references the source for the formulas. The small differences you are seeing are just due to the calculators selecting alpha and beta values in different ways but then using the exact same mathematics.

 

The formulas and values Warren Stilwell used (as he clearly states) are for the glass to be supported on four sides. Supported means that the edges are free to rotate but cannot deflect. For the purposes of the calculator, no edge of the glass is allowed to deflect at all. It is a condition of the formula chosen by Stilwell from Roark's original work. For this to be true, the aquarium must have a theoretical perfect brace (be it a glass eurobrace, the silicone joints between front and sides, a metal frame...) supporting all four sides of each piece of glass.

 

In a rimless aquarium, the top edge is unsupported and is free to deflect as well as rotate. This changes the formula in the following ways:

 

The alpha and beta values are different.

The value used to select alpha and beta is found by dividing height by length instead of length by height.

The maximum allowable stress (which gives glass thickness) is a function of the aquarium length instead of height.

The maximum deflection is also a function of the length, not the height.

 

 

Anyway, i'll put my money where my mouth is and make a calculator for rimless aquariums. It may take me a week or two. Any engineers or engineering students reading this, please send me a PM if you would like to help out by double checking my calculations. It's well over a decade since I last did any work with structures.

 

 

As a starter, I have done the calculations for the OP.

 

Minimum Glass thickness at a Safety Factor of 3.8 for a 38Lx16H is 8.87mm

With nominal 3/8 inch glass (minimum thickness 9.02mm) the maximum deflection is 1.67mm

[Cameron6796]

Are you going to cutt the glass to be shallower of a tank

[hey]

You could take a flat piece of ply and reinforce it by gluing and screwing some cross members to the bottom running in both directions. Use glued halved joints where the braces cross.

 

 

If you use a second piece of ply across the bottom of the braces, the box structure will be very strong. You could make a support frame from square steel tube or other metal stock.

 

 

 

You are finding more posts made by people who do not understand the limitations of this calculator. These mathematics will not calculate deflections, safety factors or glass thickness for rimless tanks. Using what has worked for other people however is sensible, tried and tested.

 

 

All any of these calculators do is calculate the bending stresses and deflection for a simply supported rectangular glass plate. They are all based on the same mathematics first published to the aquarium world at fnzas (check out Help/About in Aquacalc). They are taken directly from a famous engineering text called "Roark's Formulas for Stress and Strain". If you look in the excel spreadsheet calculator he references the source for the formulas. The small differences you are seeing are just due to the calculators selecting alpha and beta values in different ways but then using the exact same mathematics.

 

The formulas and values Warren Stilwell used (as he clearly states) are for the glass to be supported on four sides. Supported means that the edges are free to rotate but cannot deflect. For the purposes of the calculator, no edge of the glass is allowed to deflect at all. It is a condition of the formula chosen by Stilwell from Roark's original work. For this to be true, the aquarium must have a theoretical perfect brace (be it a glass eurobrace, the silicone joints between front and sides, a metal frame...) supporting all four sides of each piece of glass.

 

In a rimless aquarium, the top edge is unsupported and is free to deflect as well as rotate. This changes the formula in the following ways:

 

The alpha and beta values are different.

The value used to select alpha and beta is found by dividing height by length instead of length by height.

The maximum allowable stress (which gives glass thickness) is a function of the aquarium length instead of height.

The maximum deflection is also a function of the length, not the height.

 

 

Anyway, i'll put my money where my mouth is and make a calculator for rimless aquariums. It may take me a week or two. Any engineers or engineering students reading this, please send me a PM if you would like to help out by double checking my calculations. It's well over a decade since I last did any work with structures.

 

 

As a starter, I have done the calculations for the OP.

 

Minimum Glass thickness at a Safety Factor of 3.8 for a 38Lx16H is 8.87mm

With nominal 3/8 inch glass (minimum thickness 9.02mm) the maximum deflection is 1.67mm

 

So I was at my lfs today and saw a 60g rimless marineland tank. States on the box that the bottom pane only is tempered. It measures in at 24x24x24in and uses 8mm glass. Looking at it I thought man that looks too thin just based on my mr aqua 50 which is longer but a good 6 inches shorter so I put the numbers into the calc already available with a 3.8 safety factor and it comes out to a minimum glass thickness of 8.62mm. So even if the calculator is basing it on having a frame marinelands rimless is coming in under a safety factor of 3.8 which I find to be a bit scary.

[nibor]

I'll work that one out after I've been to work.

 

Edit:

 

All the following is based off the same glass characteristics as used for the other calculator. The glass used could have better properties.

 

At 8mm safety factor is 2.84 and maximum deflection is 0.88mm.

 

For a safety factor of 3.8, the glass thickness should be 9.25mm, deflection of 0.57mm.

[nibor]

Bump for hey.

[Bill_68]

Perhaps a stone slab would be best. Framing materials are just soo wet these days that I wouldn't trust it to stay flat enough to put a frameless aquarium on it. I do think the legs and frame would be fine, just not the tabletop part. Anyhow, I've got plenty of time to figure out the details.

 

[hey]

Perhaps a stone slab would be best. Framing materials are just soo wet these days that I wouldn't trust it to stay flat enough to put a frameless aquarium on it. I do think the legs and frame would be fine, just not the tabletop part. Anyhow, I've got plenty of time to figure out the details.

 

Stone slabs probably fine, As for the framing being too wet well once its all clamped up and screwed together I got my stand surprisingly level. I did have some wonky pieces of 2x4 though and it took a bit of patience getting all my plywood skinned over the frame lol.

[Bill_68]

Yep... I guess some MDF could be okay if I painted it with epoxy resin-type paint, then put on some wonder board and tiled it.