Jump to content

Tanks supported only at the edges


Dugong
 Share

Recommended Posts

Hi guys,

I saw in Cory's videos and shop that he said fish tanks are made to only require support at the bottom corners. Is this only the case for tanks with a trim around the base? Thinking of expanding fish room with 20 x 10 x 12 tanks and that would help alot in terms of cost and space but the tanks I have access to have no bottom trim.

Link to comment
Share on other sites

On 7/4/2022 at 7:45 AM, Dugong said:

I saw in Cory's videos and shop that he said fish tanks are made to only require support at the bottom corners. Is this only the case for tanks with a trim around the base? Thinking of expanding fish room with 20 x 10 x 12 tanks and that would help alot in terms of cost and space but the tanks I have access to have no bottom trim.

Rimmed tank = you support the outside walls of the tank (black trim) and you need to be careful not to add stress to the bottom glass.
Rimless tank = you need to fully support the base of the tank and very likely you want to have a rubber mat of some kind to help cushion the stress.

  • Like 2
Link to comment
Share on other sites

Thanks for the reply! Do you know why this is the case? In my mind the trim doesn't make the bottom pane of glass any stronger it just changes the contact point between the stand and tank to the edges of the tank. Effectively the same as if there was no trim and the tank is only supported at the edges.  The trim may help with the seam/seals but the seams should already be able to handle the water pressure if its being sold that way. 

Sorry not trying to be argumentative. Just trying to understand why this is the case since there is a huge time, space and money benefit for me if bottom trims aren't needed and I'd rather decide based on facts rather get rimmed tanks just in case. 

Edit: To add to this I just watched KeepingFishSimple's video https://www.youtube.com/watch?v=6OZmvydU0yo and it appears he is building a fish room with rimless tanks with only corner support. Maybe I'll wait to see how that pans out haha

Edited by Dugong
Link to comment
Share on other sites

On 7/9/2022 at 5:00 PM, Dugong said:

Thanks for the reply! Do you know why this is the case? In my mind the trim doesn't make the bottom pane of glass any stronger it just changes the contact point between the stand and tank to the edges of the tank. Effectively the same as if there was no trim and the tank is only supported at the edges.  The trim may help with the seam/seals but the seams should already be able to handle the water pressure if its being sold that way. 

Essentially, if you have a rimmed tank the load is on the vertical sides / edges / corners. So the goal is to structurally support those.  This is similar to having a wall in a house, you have structural vs. non-structural (decorative) walls.  You need to make sure the load path is through the structure!  If you have something like the bottom pane of glass on a rimmed tank with stress on it, the load itself will likely twist and cause it to shatter.

You can see a really good demonstration of this when ACO was building the store.  It's an awesome video and I highly recommend those videos.

For a rimless tank your structure is the footer. Which means, if we go back to the house analogy, your load path is the entire base/cement/floor of the building. If that shifts or deflects in some way, it is likely to cause twisting, which causes the shattering of glass.  The idea being for either situation, what is the load, supporting the load itself.

Link to comment
Share on other sites

When you fill a tank, the load is basically on the longest sides of the tank pushing outward. So let's say it's a 75G tank.

image.png.d9548ef1d4358dc793d52509377d0624.png

Essentially, these walls are bowing. pushing the seals and everything outward. the corners are your structure and it's trying to support the load. This is why the tank has that brace in the middle, to lower the deflection on those panels and to try and keep those things from causing the seals themselves from shearing off the glass. 

The most common issue is the seal itself shears off the glass in some position, usually on one of these longer panels.

The load is trying to resist this load. Supporting the walls themselves helps this issue and thing of it like a car sinking in a lake... one small crack and the window will shatter. One small stress in the up/down direction and that thing will shatter. This is why you don't load the bottom. It's a few hundred pounds of pressure and one deflection will cause it to shatter pretty easily.

With a rimless aquarium, that bottom glass is heavily loaded, it cannot deflect, which means if it does, it's going to shatter.

He has another video. He had moved his stands on 120G aquariums. A small pepple was on the stand and that ended up causing enough stress for the tank to shatter. Extremely high quality tank, destroyed by a small pebble from not cleaning the stand before placing the aquarium.

I believe this is it.
 

 

Edited by nabokovfan87
Link to comment
Share on other sites

I can agree that a pressure point anywhere on the bottom panel would cause the tank to shatter, regardless of whether there is trim or not. I also agree that trim may help strengthen the seals and a middle brace helps prevent bowing/deflection which could lead to seals shearing or side panels breaking. A trim may benefit a tank maker who thinks that glass thickness may be inadequate but a tank that's built rimless out of the factory has already proven its structural integrity and ability to hold water.

The above points don't affect what stands can be used. I don't think adding a trim just makes all the downwards load divert sideways. Unlike a house all the panels of glass are structural and even with a trim that bottom panel still needs to hold the full weight of the tank due to water pressure and gravity. The trim creates a smaller area of contact around the edges of the tank as opposed to spread evenly across the bottom entire panel. Exactly the same way a rimless tank being supported by a stand only at the edges would apply pressure only to the edges of the tank. Effectively my thoughts are if a tank can be trimmed then it can be supported with a stand only at the edges because that's exactly what trim does. 

Let me know what you think about this. I think I may experiment my self or reach out to some tank manufacturers to try get some more information. 

Link to comment
Share on other sites

Adding to your structural analogy the trim really doesn't provide much strength as its just plastic. It may help the seal and silicone the glass panels together but I don't think this relates to what stand can be used. It also reduces that contact area with the stand. 

From a simpler view the forces applied to each panel doesn't change with a stand that supports the entire bottom of the tank or just the edges. Only the contact points and pressure points of the bottom panel changes.

Edited by Dugong
Link to comment
Share on other sites

On 7/10/2022 at 12:16 AM, Dugong said:

Unlike a house all the panels of glass are structural and even with a trim that bottom panel still needs to hold the full weight of the tank due to water pressure and gravity.

This is inherently true, but might not be the full scope of accuracy.

Let's say the sides deflect 1" the bottom deflects 1/4"...... which one is really taking the stress?

That's the whole point. The difference between the two designs and the reason why the loading is different.

Specifically, I present those two as cautionary tales of "why it matters".  It's your tank and your room and your setup.  I hope you don't have any issues.  Common knowledge is as follows.

Rimmed tank: Support all 4 corners / sides.
Rimless tank: Support the entirely of the base surface equally to minimize deflection.

Keep in mind. The bottom glass being able to deflect is what allows it to actually relieve stress when under load.

Link to comment
Share on other sites

On 7/10/2022 at 5:20 PM, nabokovfan87 said:

This is inherently true, but might not be the full scope of accuracy.

Let's say the sides deflect 1" the bottom deflects 1/4"...... which one is really taking the stress?

That's the whole point. The difference between the two designs and the reason why the loading is different.

Specifically, I present those two as cautionary tales of "why it matters".  It's your tank and your room and your setup.  I hope you don't have any issues.  Common knowledge is as follows.

Rimmed tank: Support all 4 corners / sides.
Rimless tank: Support the entirely of the base surface equally to minimize deflection.

Keep in mind. The bottom glass being able to deflect is what allows it to actually relieve stress when under load.

  

Assuming the sides do deflect more this might just be a reflection of the base being silicone to 4 other pieces of glass which would act like bracing would it not? Whereas the top edge of the side panel is not silicone to anything so will deflect the most. I assume in a vacuum water pressure would be equal on all sides. However, with gravity the bottom panel will take the most load. 

If deflection allows the bottom panel to relieve stress then isnt that exactly what a stand that only supports the edges does?

Thanks very much for you help and thoughts! I do appreciate the advice. From experience many things within the hobby referred to as common knowledge aren't as simple or 100% accurate hence why I like to get into the details to understand why certain advice is given.

  • Like 1
Link to comment
Share on other sites

On 7/10/2022 at 12:37 AM, Dugong said:

Assuming the sides do deflect more this might just be a reflection of the base being silicone to 4 other pieces of glass which would act like bracing would it not? Whereas the top edge of the side panel is not silicone to anything so will deflect the most. I assume in a vacuum water pressure would be equal on all sides. However, with gravity the bottom panel will take the most load. 

A practical example / case study is the 20L aquarium compared to a 29G tall aquarium compared to a 38G aquarium.  They are all exactly the same width and length dimensions, but the only difference is the height of the tank. This directly affects the deflection.  Then you ask yourself, what amount of deflection is acceptable? A 20L deflects about a 1/4", a 29G deflect about 1/2", and a 38G has a brace.

All of those tanks have the side panel under the most stress because it is a "long aquarium" but the amount of weight and force is very different in each case.

On 7/10/2022 at 12:37 AM, Dugong said:

If deflection allows the bottom panel to relieve stress then isnt that exactly what a stand that only supports the edges does?

Think of it like styrofoam. Allowing it to deflect absorbs force, but it doesn't specifically return to it's normal form when it is unloaded after receiving stress. Glass is a liquid, not a solid. It can relive stress by flexing, but not necessarily by twisting. That's when you run into issues.

On 7/10/2022 at 12:37 AM, Dugong said:

Thanks very much for you help and thoughts! I do appreciate the advice. From experience many things within the hobby referred to as common knowledge aren't as simple or 100% accurate hence why I like to get into the details to understand why certain advice is given.

I totally understand. I hope the explanation makes sense and is helpful. If it isn't, I totally understand!

Link to comment
Share on other sites

On 7/10/2022 at 5:42 PM, nabokovfan87 said:

A practical example / case study is the 20L aquarium compared to a 29G tall aquarium compared to a 38G aquarium.  They are all exactly the same width and length dimensions, but the only difference is the height of the tank. This directly affects the deflection.  Then you ask yourself, what amount of deflection is acceptable? A 20L deflects about a 1/4", a 29G deflect about 1/2", and a 38G has a brace.

I agree that  taller tanks have more volume and hence more force on the tank sides and that the glass deflects and after a certain amount of deflection you have a wet mess.

However, I don't see how this relates to why trimmed tanks can be supported at just the edges and rimless do not. The bottom trim is usually just plastic and would provide minimal structural support. The whole weight sits on the trim at the edges. The same as the whole weight at the edges on a rimless tank in a stand only supporting the edges.

On 7/10/2022 at 11:06 PM, BuzzDaddy21 said:

I`m kind of dumb here but what kind of stands are you talking about (I have a vague idea.) I think that whatever is used as long it is level that is what counts.

A good example of a rack only supporting the edges is at Aquarium Co-op.

 https://youtu.be/y4oYu8C-RhU?t=118 

However, they're tanks have trim around the bottom. My question is whether this trim is needed. I don't see why it wouldn't work without it because it's just plastic. If I were just going to build 1 stand/tank then I would just play it safe use a rimmed tank. But I am considering expanding my fish room by over 15 tanks so it does make a difference. 

Here's a picture with a tank with no trim and no middle support. 

853046F6-379C-46F9-AC33-159363F01247.jpeg

 

Edited by Dugong
Link to comment
Share on other sites

  • 2 weeks later...

After some research and talking to a couple manufacturers I thought I'd post an update incase anyone was curious down the line. 

The trim around the bottom of tanks don't provide any structural support and are mostly for aesthetics. They do function to lift the tank up causing it to be supported at the edges only, even when on a flat surface, which is why a stand with no centre support is the same. The reason why some trimless tanks cannot do this is because the glass at the base is too thin which requires the whole bottom pane to be supported. 

In summary, trimmed tanks can be supported only at the edges. Trimless ones - it depends on the thickness of the glass. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...