Slight gap in corner of top glass surround.

[LouH]

I just moved my tank and noticed that there is a 1/16" gap in the miter joint of the top surround. Should I be worried? An important piece of information is that my tank has always been supported by a piece of styrofoam under the bottom pane of glass. The bottom surround is elevated about 1/8" off of the top surface of the stand. I've researched this and I have yet to see anyone say that what I'm doing is safe. However, my tank has been supported like this for about 7 years. Is my tank on its way to a failure?

Lou

[LouH]

Looking at the bottom surround for the tank, it doesn't appear to provide significant structural integrity to the tank. It is made up of four pieces just like the top surround, and it is attached to the base with silicone. It has miter joints at the corners, just like the top surround.

I can't see which edges are supported by the surround. If the side panels are supported by the surround, then bottom panel joints are stressed by shear as the weight of the water pushes down on the bottom panel. Basically, the weight is trying to break the silicone joint that holds the bottom to the sides in a downward vector. If the surround supports the bottom pane of glass and the side panels rest on top of it, then the silicone that attaches the side panels to the bottom experience a tension strain/stress as the weight of the water pushes outward on the glass panels (of course force is being applied in all directions at once, I'm simply considering the direction in which the joints see the most strain). My tank is 72" long and has a center brace to keep the tank from bowing. The center brace is 2" long so the total length of silicone taking up that force is 4 linear feet.

There is no center support that attaches the front bottom support to the rear bottom support. This makes me believe that the side panels rest on the surround and the center floats or is under shear. Essentially, the bottom panel of glass acts like a big center brace.

If the bottom panel is resting on styrofoam, then the contact area of the bottom panel would minimize the shear forces seen by the bottom silicone joint. To me, this arrangement would put the least amount of strain on the bottom joints.

If the bottom surrounds simply reinforce the panel joints like pieces of angle iron, then I believe that the shear and tension forces seen by the panels would be the same regardless of how the tank sits on a surface.

Lou

[sirreal63]

If the tank has a bottom trim piece then you should not use foam under it. I would probably drain some water out and inspect the seal very carefully.

[LouH]

My comments were in regard to failure modes based on joint stress. I searched some more and found statements that claim that the purpose of the trim piece is to elevate the bottom panel to ensure that point loading of the bottom panel/pane cannot occur. Point loads will lead to a broken panel. There are those out there who state that supporting the tank with styrofoam leaving the trim pieces unsupported is OK, although they are very much in the minority.

I thought about my earlier comment regarding panel configuration and its relatoinship to shear strain vs tension strain. After further consideration, the force exerted on the bottom seams is the same regardless of panel configuration.

Regarding the function of the bottom perimeter trim, from what I can see, it does function act as joint reinforcement. It functions as angle iron which supports the joint and holds it together via silicone. Again, if I think about it in these terms, I can't see how supporting the tank with styrofoam is a compromise to letting it rest on the perimeter trim.

I'm not an engineer, so all of you engineers out there are encouraged to chime in. I read a lot of statements that say that you should not do what I have done, but none of it speaks to why it is the preferred configuration in terms of physics/engineering. What are the failure modes and which are most likely based on how the tank is constructed?

Lou