Your tank is TOO SAFE! Yeah, I said it - it's TOO SAFE!

[coolkeith]

There's cheap insurance to increase the safety margin then there's overkill.

If you want to kill an ant do you step on it? Run over it with a truck or drop an atom bomb? Do you reeealy need an atom bomb to kill an ant? You want to make sure it's dead so it doesn't come back to bite you but come on.... I'm just saying it's a waste of time and money. If somebody doesn't mind spending the time and money that's their prerogative. But I just sit here and shake my head at the overkill.

Sashi- don't take this wrong, but from what I know, you've only built a 7 footer and have only had it a few years. I think your tank is awesome BTW. But when you get to 8+ feet, there's a lot more of the unknown going on. My DIY 8 foot tank only lasted 4 years because it was under-built perhaps. After about 2 years, the wear and tear started to become noticeable. By year 3, warping on the plexi and bowing was beginning to worry me. By year 4, there was cracking/crazing in most of the seams, so I replaced the tank before it eventually failed.

Now a 7 foot tank, like the one you built, might not ever have those same problems, but an 8+ footer could. My next big tank build, if it's over 8+ feet, will be overkill, even if you are shaking your head. I don't understand the over-confidence, especially since you have a mechanical engineering degree. You should know that even the best laid plans can fail. I remember some of the lab assignments I had when I was taking engineering courses, and it seemed like human error was a common conclusion in many of my technical reports. Engineers aren't perfect.

 

[sashimimaster]

Sashi- don't take this wrong, but from what I know, you've only built a 7 footer and have only had it a few years. I think your tank is awesome BTW. But when you get to 8+ feet, there's a lot more of the unknown going on. My DIY 8 foot tank only lasted 4 years because it was under-built perhaps. After about 2 years, the wear and tear started to become noticeable. By year 3, warping on the plexi and bowing was beginning to worry me. By year 4, there was cracking/crazing in most of the seams, so I replaced the tank before it eventually failed.

Now a 7 foot tank, like the one you built, might not ever have those same problems, but an 8+ footer could. My next big tank build, if it's over 8+ feet, will be overkill, even if you are shaking your head. I don't understand the over-confidence, especially since you have a mechanical engineering degree. You should know that even the best laid plans can fail. I remember some of the lab assignments I had when I was taking engineering courses, and it seemed like human error was a common conclusion in many of my technical reports. Engineers aren't perfect.

Well I guess I'll give you an update after another year and see how it holds up. As you've read already the amount of load is not dependent on the length but the height of the water column. So whether it's 7ft, 8ft or 1000 ft long it's irrelevant.

 

[bulldovii]

Well I guess I'll give you an update after another year and see how it holds up. As you've read already the amount of load is not dependent on the length but the height of the water column. So whether it's 7ft, 8ft or 1000 ft long it's irrelevant.

Very true. Can you really be too safe when it comes to your prized possession whether that's your house or your tank? One persons overkill is another person's insurance.

Sent from my Amazon Kindle Fire using MonsterAquariaNetwork App

 

[coolkeith]

Well I guess I'll give you an update after another year and see how it holds up. As you've read already the amount of load is not dependent on the length but the height of the water column. So whether it's 7ft, 8ft or 1000 ft long it's irrelevant.

You shouldn't be saying that the length of the tank is irrelevant. The water pressure is the same along the horizontal span, you are correct about that, but the deflection of that water pressure along the walls isn't the same, which is why we get more bowing the longer the horizontal span is.

I don't think the sides of your tank will fail since it's only 7 foot. I hope the bottom doesn't fail either, but since it's already bowing, like you said it is in your thread, you might have some future problems. Every time you change the water height or do water changes, you change the pressure on the bottom, thus bending it back and forth, and weakening the joint. I'd suggest a continuous drip system, if you already don't have one.

 

[Desdinova]

Sashi- don't take this wrong, but from what I know, you've only built a 7 footer and have only had it a few years. I think your tank is awesome BTW. But when you get to 8+ feet, there's a lot more of the unknown going on. My DIY 8 foot tank only lasted 4 years because it was under-built perhaps. After about 2 years, the wear and tear started to become noticeable. By year 3, warping on the plexi and bowing was beginning to worry me. By year 4, there was cracking/crazing in most of the seams, so I replaced the tank before it eventually failed.

Now a 7 foot tank, like the one you built, might not ever have those same problems, but an 8+ footer could. My next big tank build, if it's over 8+ feet, will be overkill, even if you are shaking your head. I don't understand the over-confidence, especially since you have a mechanical engineering degree. You should know that even the best laid plans can fail. I remember some of the lab assignments I had when I was taking engineering courses, and it seemed like human error was a common conclusion in many of my technical reports. Engineers aren't perfect.

This is a real eye-opener. I see so few people go back into their threads and comment about what happened these years later. I started this thread, because I was feeling like I had scared myself into believing that I needed the atom bomb to kill the ant, but you're helping me think through this with comments like these.

I'm still not convinced that layering lumber is necessary. A basic frame still seems just fine, but I will be paying close attention to the window. I let some people talk me into believing that a 2.0 safety factor is good enough, but I think I should learn from you and insist on something higher. I want it to work 10 years down the road, not just the few month.

That said, I thought of an interesting idea today. Imagine having a tank that uses 8 foot sheets of acrylic for the windows and it's 24 feet long. Instead of putting 6x6 beams between them, wouldn't it be nicer to get a beam make of acrylic? I'm not sure what a 6x6 acrylic beam would cost, but if it would hold well enough, it would be clear... So clear acrylic, clear silicone, clear pillars?

 

[sashimimaster]

You shouldn't be saying that the length of the tank is irrelevant. The water pressure is the same along the horizontal span, you are correct about that, but the deflection of that water pressure along the walls isn't the same, which is why we get more bowing the longer the horizontal span is.

I don't think the sides of your tank will fail since it's only 7 foot. I hope the bottom doesn't fail either, but since it's already bowing, like you said it is in your thread, you might have some future problems. Every time you change the water height or do water changes, you change the pressure on the bottom, thus bending it back and forth, and weakening the joint. I'd suggest a continuous drip system, if you already don't have one.

The only reason why it bowed is because I didn't seal the glass well enough and it got wet. I've since resealed it and everything is ship shape. With 4+ layers of fiberglass there isn't any flexing at all. I guess the only way we'll really know is over time.

As far as deflection over the length you are assuming that the walls are unsupported from above. If you have cross beams tying the top across the length there shouldn't be any issues.

 

[coolkeith]

This is a real eye-opener. I see so few people go back into their threads and comment about what happened these years later. I started this thread, because I was feeling like I had scared myself into believing that I needed the atom bomb to kill the ant, but you're helping me think through this with comments like these.

I'm still not convinced that layering lumber is necessary. A basic frame still seems just fine, but I will be paying close attention to the window. I let some people talk me into believing that a 2.0 safety factor is good enough, but I think I should learn from you and insist on something higher. I want it to work 10 years down the road, not just the few month.

That said, I thought of an interesting idea today. Imagine having a tank that uses 8 foot sheets of acrylic for the windows and it's 24 feet long. Instead of putting 6x6 beams between them, wouldn't it be nicer to get a beam make of acrylic? I'm not sure what a 6x6 acrylic beam would cost, but if it would hold well enough, it would be clear... So clear acrylic, clear silicone, clear pillars?

Stacking lumber isn't necessary, but it does serve more than one function. Obviously, it adds a lot of strength, but also like I said before, it dampens sound/ vibrations and retains heat better than just plywood alone. If you're building next to an exterior wall, up north where it gets really really cold, you might need that extra barrier to ward off thermal changes and moisture.

You may need that added strength for other reasons too, if you have dogs, children, or drunken friends banging on or jumping into the tank. If you live alone, and never have crazy people over, then you probably can get away with building it cheaply.

and I've sworn off acrylic. I don't like how it absorbs water and warps over time. The thinner stuff bows too much, and the thick stuff gets really expensive. I'd prefer smaller glass panels that are no more than 6 foot long, rather than larger acrylic windows.

 

[coolkeith]

The only reason why it bowed is because I didn't seal the glass well enough and it got wet. I've since resealed it and everything is ship shape. With 4+ layers of fiberglass there isn't any flexing at all. I guess the only way we'll really know is over time.

No flexing? In your thread, just last month you said:

Yup, since I had to piece together two pieces of plywood I wanted to use the tongue and groove osb. I fiberglassed it so it's stiffer but it still flexes a little. Even with bracing spaced 18" apart when I step on it I can feel it flex. There's no issue with leaks because the entire tank is glassed and Wetsuited but if I was to do it again I'd think about using regular plywood.

I doubt this will be an issue for you, but any kind of flexing might eventually cause crazing, which leads to cracking, then to leaking. I would of doubled up the plywood on the bottom, or braced the bottom with no gaps, so it's rock solid like a butchers block. The later is huge overkill, but the cost shouldn't be much. You done a wonderful wonderful job waterproofing your tank. You probably won't have the same kind of issues that I'd run into with a larger tank. I'd even think about pouring a solid concrete floor for the bottom for the tank and just seal that, so that I could avoid stitching together those plywood seams.

As far as deflection over the length you are assuming that the walls are unsupported from above. If you have cross beams tying the top across the length there shouldn't be any issues.

It's depends on the height and length of the tank, relative to the glass thickness. There have already been a few good examples in this thread.
See your above comment as another example. Even with bracing every 18", the bottom still flexes a little. The strongest part of the tank is the corners, because it's reinforced vertically and horizontally. The longer the span is without reinforcement, the more deflection there will be. I've written engineering programs to calculate deflection and what exactly the safety factor is. I've built tanks and stands using some of those minimal safety factors without much long-term success. So I've learned my lesson the hard way, and now tend to overbuild things. Much of what you see commercially these days, like OSB aquarium stands, and that cheap piece of crap above ground swimming pool, probably won't last long.

 

[sashimimaster]

No flexing? In your thread, just last month you said:




It's depends on the height and length of the tank, relative to the glass thickness. There have already been a few good examples in this thread.
See your above comment as another example. Even with bracing every 18", the bottom still flexes a little. The strongest part of the tank is the corners, because it's reinforced vertically and horizontally. The longer the span is without reinforcement, the more deflection there will be. I've written engineering programs to calculate deflection and what exactly the safety factor is. I've built tanks and stands using some of those minimal safety factors without much long-term success. So I've learned my lesson the hard way, and now tend to overbuild things. Much of what you see commercially these days, like OSB aquarium stands, and that cheap piece of crap above ground swimming pool, probably won't last long.

Flexing in the floor not the walls. And that was with a point load from me stepping on it. With a distributed load there is no flexing. And when I say flexing we're talking about mm not inches here. Between the fiberglass and wetsuite which can stretch to over 100% there isn't a problem.

Again, time will tell.

What size is your tank that you built?

 

[Pharaoh]

Certainly. I suppose I'm guilty of assumption in this case. I don't know of any places that will make sheets longer than 8 feet, so I tend to assume that this would be the max distance of a single sheet. However, I'm wrong about that. But if you decide to frame sheets of 8 feet each, this shouldn't be an issue - as far as I know. Please do correct me if I'm wrong: I'm saying that if you have an 80 foot tank with 9 vertical pillars and ten 8 foot sheets of window, then the windows wouldn't have to be thicker just because it's a long tank.

In that case, no the windows would not need to be thicker. This is because you have joined them and added support. The pressure exerted does not change based on length.

I do beleive I understand what you are getting at. Most members put a lot of additional bracing on the outside, but possibly forget about the same said support design when it comes to the bottom of the tank and there is the greatest amount of pressure exerted. So the basic question, why so much attention to the sides and not the bottom?