How much overhang is ok

[Daniel]

2 hours ago, TheDukeAnumber1 said:

Beam analysis may be a good guide here. Since we know a 10g can be supported on its ends in a simple span condition and we can approximate overage with a cantilever beam condition.

Thinking moment governs and equating simple span to cantilever span and solving.

w*lx^2/8 = w*ly^2/2

lx = 2*ly

Supporting on ends is the same moment as half the tank hanging off the table and arguably better since the bottom will be braced in compression and arguably not since this is glass and not the governing mode of failure. ¯\_(ツ)_/¯

In a nutshell though you are probably just fine as shown in the picture.

I am not so good at beam analysis, but I have setup aquariums with overhangs very similar to that pictured without any failures. Not saying full support wouldn't incur less risk, just saying I have done janky stuff like that without having the tank break or leak.

[TheDukeAnumber1]

52 minutes ago, ererer said:

 

Beams do flex though, and I think it's more likely a failure will occur due to flexing at a seam causing a leak than from a glass panel breaking. I've personally never tried supporting an aquarium only by the corners, so I'm not personally suggesting that either. Will a failure take years to show up if it ever happens? Probably. We don't know how old this aquarium is or what shape the seams are in already though either.

Flexing depends on load and in this case it is very similar between the two conditions with the overhang case having less deflection. Which makes me think it would probably be ok.

[StephenP2003]

1 hour ago, Daniel said:

I am not so good at beam analysis, but I have setup aquariums with overhangs very similar to that pictured without any failures. Not saying full support wouldn't incur less risk, just saying I have done janky stuff like that without having the tank break or leak.

I have a fluval spec 16 that deliberately is designed to overhang via a built-in "stand" underneath it, so there's a couple inches of overhang on all four sides.

 

 

[Jungle Fan]

@erererThe tanks that failed because of lack of mid-center support were likely acrylic tanks, as they need complete support and a mat to distribute and support the weight evenly, glass tanks without frame should also should have a mat, framed tanks need even support only under the frame. My 75 gallon's frame rests on a metal frame inside the stand that is supported by leveling feet, if I had nothing inside the tank you could look down through the glass into the stand to see the filter, and CO2 equipment.

[Jungle Fan]

Found this picture of when I was still experimenting with the roots for the hardscape, and had not finished and sealed the slate door inserts yet. You can see down into the stand and see the powerstrip on the wall through the bottom of the tank, as well as the metal frame.

[Eric R]

50 minutes ago, Jungle Fan said:

The tanks that failed because of lack of mid-center support were likely acrylic tanks

Red Sea XXL750s are made of 3/4" high clarity glass. They are rimless though, I'm not sure what difference that makes. To be clear, I'm not talking about supporting the exact middle of the tank, just the outside frame.

Very nice stand btw!

 

1 hour ago, StephenP2003 said:

I have a fluval spec 16 that deliberately is designed to overhang via a built-in "stand" underneath it, so there's a couple inches of overhang on all four sides.

 

 

I would be careful applying anything from a tank that's designed to be elevated to one that's likely designed not to be elevated. There may be something to be learned by looking at how the tank is designed so that it can be elevated, and how the bottom of the tank is supported.

Edited March 9, 2021 by ererer

[StephenP2003]

1 hour ago, ererer said:

I would be careful applying anything from a tank that's designed to be elevated to one that's likely designed not to be elevated. There may be something to be learned by looking at how the tank is designed so that it can be elevated, and how the bottom of the tank is supported.

Valid point for sure. As far as I can tell, the biggest difference between this fluval spec and a standard 10 gallon is glass thickness. The spec uses 1/4" glass so it's got the extra safety factor going for it. It is rimless, however, so the four corners are not touching anything. Like Daniel though, I've done some ill-advised things with tanks 20G and below, without consequences. Better safe than sorry anyhow.

[Jungle Fan]

Glass is more rigid than acrylic, which is flexible and the bigger the tank the bigger the stress that's why acrylic needs complete support and a mat because it can bow and bust. Framed glass tanks tend to use thinner glass than rimless because the manufacturers figured out they can get away with lesser strength glass because of the added support of the frame and in some cases brace, which is also the reason why most state in their warranty that it is null and void when the frame is removed, or altered. Framed glass tanks actually don't make contact with the stand as the glass makes contact only with the frame and all the stress in glass tanks rests on the seams, which is why they are the most important part to inspect before you buy.

In rimless tanks the weight is still resting primarily on the seams but since the whole bottom makes contact with the stand and due to limitations in the glass manufacturing process the strength of the glass can vary ever so slightly that it isn't perceptible to the eye, and unevenness in the surface, or grit in the stand finish can cause point loads on the glass surface that can cause the tank to fail which can be avoided by simply using something as cheap as a yoga mat which can be cut to size  with a knife. Now for all it's worth I'm no structural engineer but that is the explanation I was given by a glazier who has supplied glass for quite a few aquariums, and following this guideline has served me well so far,