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eug 06-10-2012 08:03 AM

Did something stupid - Removed braces
Hi DIYers

Quick summary, I have a tank measuring 80cm long, 35 cm wide and 45cm high. The tank came with pieces of glass about 3-4 cm wide, about 80% of the front glass length, siliconed at a 90 degree angle to the top of the front and back glass panes. It appeared to me like it was designed to simply hold for example a clear glass top, which I don't have, and I felt it was blocking some light as it got dirty so I decided to take a knife and cut the silicone and remove the glass pieces.

Doing some further reading on the issue (of course I act first, read later, typical...) it became clear to me that these glass pieces serve (or served rather) as more than supports for covers etc, but rather as braces to prevent bowing.

The glass is 6 mm thick, and looking around at glass thickness calculators, this puts it in the "safe" region for these dimensions.
Calculate Aquarium Glass Thickness | Aquarium Tools

But nonetheless, I've measured the width on the sides of the tank, and it's 34.9 cm on both sides. The measurement in the middle of the tank front-to-back is 35.3 cm, which means the glass is bowing out about ~2 mm on each side (front and back).

Is this cause for panic? To make matters worse, I've dropped and broken one of the original braces, making it impossible to attempt to silicone it back on. So, if the tank definitely needs bracing, I need a new solution.

One idea I've had is to somehow attach some steel wire in the center to brace the tank in the middle, which also would block out less light than the original braces. What do you guys think? Thankfully the tank isn't inhabited by fish yet, but still I'd rather not have the glass panes crack on me, although that goes without saying!

eug 06-10-2012 09:37 AM

Sorry, I got my tank dimentions wrong, it's 40cm high not 45cm, meaning according to that calculator it raises the safety factor to 3.

eug 06-14-2012 09:35 AM

Heh, didn't exactly get the desired response here...
Basically what used to be in place were semi Euro-braces, kind of a half-assed version where only the long sides are supported. It's a really common method it seems in German tanks.

I felt pretty stupid reading how essential these are after removing them, and wasn't too pleased to see the glass bowing about 2 mm on each side - but then again, I wasn't satisfied with how the tank looked originally (I did remove them for a reason, after all) with the sloppy silicone job and the fact that the braces didn't sit flush with the top of the tank, so I figured I might as well do some thinking and find an alternative that is just as physically stable but also visually pleasing. Went to the hardware store in hopes that inspiration will strike when I find the right materials...

So the idea with euro-bracing is that a strong enough perpenticular lateral brace is applied to the tops of the glass panes, which supresses the hydrostatic pressure of the water from causing the aquarium glass to bow out, which can of course result in leaks at the silicone seams and/or glass breakage. I considered just going to the glass-maker and having custom glass cut to replace the one I broke, but over at the hardware store I found a suitable deputy. As the picture shows, I've used aluminum molding, with a 90 degree bend, about 1 cm on the short side, and 4 cm on the long side. When putting the long side perpenticular to the tank glass along the top edge, I figured it should provide more than enough strength to keep the glass from bowing to dangerous levels. I removed enough water so that the bowing of the glass was little enough that I could clamp the aluminum bars on without difficulty, and took some silicone (which bonds happily to both glass and aluminum) to attach the braces. I let it cure for 24 hours, and being nearly certain that the silicone had cured, removed the clamps. Satisfied that the tank, being only partly full, showed hardly any signs of bowing, I went ahead this morning with filling it up the rest of the way, crossing my fingers that the braces will hold. The result:

I left some space at both ends of the braces to allow space for cables and tubing. The glass at the corners measures exactly 35 cm, and the aluminum is a bit over 2 mm thick, and a thin layer of silicone also needs to be considered, so with 0 bowing we're looking about a target of 35.5cm or thereabouts from pane to pane in the middle. Some bowing is still to be expected, so I took the German industry standard of length/500 as the tolerance level for bowing, so a glass length of 80 cm means 800 mm / 500 = 0.16 cm or 1.6mm, the maximum allowable distance pane-to-pane would then be double that at 3.2mm plus the length of the sidepanes of 350mm, so 353.2 mm would be the upper limit of these tolerances. Note that when I measured the bowing with the tank full without any bracing, the pane-to-pane distance was 354mm, so it was no longer within the set tolerances, and the reason why the manufacturer chose (or was forced to) put the original braces in place.

Anyway after filling the tank with the new aluminum braces, the pane-to-pane distance (after subtracting the estimated 5 mm of thickness of the aluminum and silicone on both sides combined) is 351 mm compared to the measurement of 350mm when the tank is empty- that's right, although I can only get a fairly rough measurement using a standard tape measure, that means only about about 0.5 mm of bowing on each side, well under the 1.6mm industry norm. Even allowing a millimeter of margin of error due to inaccuracies in the measuring procedure, I'm within tolerances here so I'm pretty happy with the result.

Varkolak 06-14-2012 09:54 AM

Looks like you did your research well and your tank looks unique now, I kinda like the white contrast myself. Glad you got it all worked out

eug 06-14-2012 11:01 AM

Hmm, am I in trouble?

I just noticed in the upper right, near the end up the aluminum brace that there's a possible hairline crack. If I'm optimistic, I would say it's just a scratch, but my gut says otherwise. I don't know how a scratch that deep could have been made without my noticing. People with possible engineering backgrounds - is this a likely place for such a crack to appear? Is there a structural fault in the way I've built the brace that might cause such a crack? Or is it more likely to be a scratch that I don't need to worry about...?

eug 06-14-2012 11:14 AM

I should add, I can only feel the crack/scratch on the outside.

SinCrisis 06-14-2012 01:36 PM

Looks like its just a scratch, it should be fine. If it was a crack you would be able to see it run through the class instead of just on the surface.

As for your bracers, are you seeing any bowing now? With any modifications like this, you run the risk of moving stress from one point on the tank to another point, which can cause damage in other parts of your tank. Your mod concept seems very similar to the original, so it should be fine. I would just be careful with it and check it a lot over the next couple of months to be sure.

eug 06-14-2012 01:39 PM

Yeah, I'm starting to think it's just a scratch probably caused by sloppy removal of clamps - I was possibly a bit antsy to see if the silicone was going to hold or not. I used C clamps, and I checked how far down the clamps go, and what do you know, the scratches only go as far as the clamps can reach... I say scratches because I found a similar scratch, but this time on the inside of the tank in a similar spot, but a bit further into the middle. So that is starting to look like accidental scratching, but I marked the ends of the scratches with a marker to keep an eye on it over the next while to be sure.

eug 06-14-2012 01:43 PM

And yes, I am hoping that because it's similar in concept to the original it should be fine. The only concern is that because the brace is longer than the original, but doesn't completely reach the side panels, it might mean there's increased strain on the edges of the front and back panels, as well as the vertical silicone joints. Also, the aluminum is attached to the outside of the glass, which is different from the original which was attached to the inside.

The bowing has been cut down to .25-.5mm on both sides, so bowing has been practically eliminated, but as you mentioned it's the possibility that there's increased stresses in other areas due to the slight changed location of the brace (worries me less) and the increased length of the brace (worries me more).

lorax84 06-14-2012 01:56 PM

I personally would get some glass cut and try to recreate the original bracing. Depending on the alloy of aluminum in the bracing you have created, it may not provide much rigidity at all. Since it is not a huge tank you may be okay but if you do have a problem it will probably be a catastrophic failure, not a leak.

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