View Full Version : Unusual "tank" questions
Nafnlaus
01/08/2014, 10:38 PM
I'm in the design phase of building a new home, and I had an unusual design concept that you all probably have more experience with than just about anyone else. I want at least a bathtub - and possibly a small shallow outdoor balcony hot tub as well - to be like a fish tank. That is, the bathtub would have one transparent wall (likely inserted into the concrete before it's even set, so that it's securely fastened and watertight... though with glass it'd probably be inserted into a slot to allow for thermal expansion), and the rest would be natural-looking, irregular shaped (formed from the concrete of the home), maybe with soft sand on the bottom (french drain or the like for draining water from it), mossy rocks, and so forth. If I did the outdoor balcony hot tub too, it'd have no sand or rocks, probably two transparent sides, and a transparent bottom. Significantly reinforced, of course.
Really, the construction requirements sound a lot more like fishtank construction requirements than anything else... so that's why I'm here!
First off, I wonder what you all think of this concept. Does it even sound reasonable? Or are bathing humans just too much of big clumsy animals to be trusted around transparent materials?
The other questions have to do with construction.
First, what sort of material would be best? I've been thinking about acrylic, polycarbonate, and glass. I think I'd have to rule out the polycarbonate for outdoors because it's more UV-susceptible than acrylic. For indoors, it is majorly more fracture resistant and tolerates heat better... but then it bends a bit easier, and it's easier to scratch. So I don't know. Then on the other end of the spectrum is glass.... no problems whatsoever unless it breaks, wherein suddenly it's *big* problems.
(I don't care much about transparency/optical quality issues... any transparency is better than no transparency!)
Then comes the subject of bracing. From the calculators I've seen, it looks like a long piece of acrylic, for example, braced on top supporting 60cm / 2 feet of water, requires 2cm / 0,8in acrylic. But 60cm squared required is only 1,2cm / 0,5in acrylic. Does that mean that if there were vertical bracings every 60cm / 2 feet that one could use the thinner acrylic? What if one had additional reinforcing bar at an angle against the middle of each of the 60cm squares, could the plastic be thinner still? Again, while reinforcing obstructions aren't ideal, any transparency is better than none, and if reinforcement can lead to significant raw materials savings.... :)
And speaking of heat earlier... how does water temperature affect the required thickness? I mean, we're not talking boiling, but it could get to 40C (104F), maybe even more. I know polycarbonate is more heat resistant than acrylic... and then of course glass is pretty much indifferent to temperature, assuming there's enough room to handle thermal expansion.
Another question is layers. Can one use two layers of 0,6cm / 0,25in acrylic (or whatever) bonded together in place of one layer of 1,2m / 0,5in acrylic? I imagine it'd lower optical quality, but again, that's not the main issue (unless it completely destroys it). Are the strengths roughly equivalent? The reason I asked is that I priced panels and 0,6cm / 0,25in acrylic is a third the price of 1,2m / 0,5in, not half price, so using a double layer of it would save 33% of the cost of the plastic.
(Of course, these prices were from overseas; I have no idea what prices here in Iceland will be like, they can be weird sometimes! I also haven't priced glass at all. Polycarbonate was (surprisingly) only marginally more expensive than acrylic)
Anyway, I'm just trying to get a sense of general project feasibility, thoughts, and recommendations. :)
Joe0813
01/08/2014, 10:51 PM
I'm lost with your plan... do you want something that you sit in with fish? Or is bath tub just a big tank that you look at?
Whiterabbitrage
01/08/2014, 11:02 PM
Or is it just for people, no fish? You just want to watch your girlfriend.....?
SGT_York
01/09/2014, 07:38 AM
This fits into one of those categories that you will require a professionally certified engineer and a specialty trades contractor. This is not something you can DIY if you are asking these types of questions.
That being said look to spend a pretty penny.
pwreef
01/09/2014, 08:44 AM
You want to put sand and mossy rocks inside your home? Where you will bathe with that?
Gsxr600
01/09/2014, 09:06 AM
yea im not sure if you want to keep fish or youre looking for a natural type of bath tub??
thats being said if it is to house fish, think about the long run of things. are you going to keep up on maintenance on something that seems like it would require a lot of care? seems like its something that if you get bored with it or it turns out to be problematic, will be an eye sore in youre new home. and if you are to ever move out of the home, it could kill resale. new home buyers gunna be like *** am i gunna do with this?
if you are trying to keep fish/reef id say just plan out a designated fish wall/room and do all the plumbing work before all the sheet rock and what not goes up.
Schplitter
01/09/2014, 09:15 AM
It is feasible and has been done before. Some Vegas hotels have those features. Very cool but not practical at all.
What you will need to do is to construct the concrete then insert the acrylic with a seam then fasten it. All of this will require an engineer to make sure everything is strong enough.
You are talking about .25" acrylic or .5" acrylic above. You will need to look at 3", 4" or even 5" thick acrylic so you don't end up with bowing over time. The temperature will also make things more flexible and add to bowing.
I don't think you should look at it as a fish tank build but more of an pool build. The reason I'm saying this is because of the irregular pressures you will have in the tubs. Lets say you have all the water churning and heating in there then you decide to go into the tub. That will add a lot of pressure all at once to everything.
Good luck with this!
SGT_York
01/09/2014, 11:04 AM
It is feasible and has been done before. Some Vegas hotels have those features. Very cool but not practical at all.
Good luck with this!
As I said this is a professional level engineering feat not a DIY project.
Joe0813
01/09/2014, 12:51 PM
i just dont get what hes trying to do? how can you bathe in a tub with fish? first off its dirty and second all the oils and everything that comes off your body could potentially kill the fish or corals (if you have coral)
SGT_York
01/09/2014, 01:29 PM
it's for a fish tank the same size as a bathtub or using a bathtub for parts, not for actually taking a bath.
The major engineering feats, are the support, calculating the correct height, and properly determining how to seal the concrete and bond it to the acrylic. By suggesting to use a bath tub he's trying to go with a low priced solution, but the proper way to bond the acrylic to plastic or to concrete is difficult and expensive. Leave this to the Tanked crew or some other bonded, insured contractor.
jeromeit
01/09/2014, 01:53 PM
I would definitely leave this to a pro, you dont want a mess thats for sure.
Nafnlaus
01/09/2014, 03:05 PM
No fish. Just a tub. Sorry, I thought when I said "bathtub" that it would be a given that there were no fish. But since it would be a transparent water-holding structure, I figured it had more in common with fish tanks than regular bathtubs, so I asked here. Certainly "bathtub people" know nothing of working with acrylic structures that hold a heavy mass of water!
Schplitter: Are you saying 3-5" because of people bumping into / pressing on things, or because that would be needed to contain the water? I used several acrylic calculators I found online and they all said the same thing... at 2' of water, 0,8" for a long panel, 0,5 for a square panel (and hence the reason I was asking whether reinforcements could make it more like a square panel). But your point about "irregular" forces is a good one and one that I'd been thinking about. Hmm... you know, I can do the math on that... I'll do that at the end.
Do you know of anyone who's done a task like this before that I could talk to, whether an engineering firm or private individual? Because I can be pretty sure of two things: 1), I'm sure it's been done many times in the world (for example, as you mentioned, fancy vegas hotels), and 2) that there's nobody in *Iceland* who knows how.
Okay, forces... let's see.... that much water would be 5,8 kPa at the bottom... times, say, three square meters, that's 17,4 kilonewtons (about 4000 pounds of force) - pretty impressive! Of course, the strain will vary depending on how far you are from reinforcements - toward the edges, the reinforcements will bear part or all of it. Now, if I remember right, tanks are usually build with a safety factor of about 3,5, so thats about 60kN total.
Now, I can see four potential types of impacts: impact shock from outside in, impact shock from inside out, impact shock against the top, and braced pressure from between two hard surfaces.
Impact shock from the outside in shouldn't be a problem - you're *helping* the tub hold the water in ;) The worst you're doing is making waves that will come back and inpact the side. But we all know waves don't pose a thread to an aquarium.
Shock or persistent pressure on the top should be irrelevant given that the top rim would be braced.
Impact shock on the inside is obviously a real concern. But it does have one thing going for it - it's hard to move fast in water, and thus build up energy. I think the worst case would be in the "spa" scenario, where a person could jump right feet first on top of a (reinforced) plexiglass floor - I doubt two feet of water would do much to soak up that energy. Let's say they can fall about a half meter and they weigh 70 kilos. That's 343 joules - 343 newton-meters. Now it gets tricky because we have to know how much it deforms to determine how long the tank has to absorb the shock (longer deceleration time = less force). If we assume in this extreme event that the tank would break after bending out 30cm before, then the tank would face up to 114 kN of force for the impact. Even if we assume that passing through the water absorbs part of the energy, this would still break the tub if they landed as far as possible from a reinforcement. We see that should I build one with a clear bottom, the thickness for the bottom should be double or so to have a safety margin that can handle these sorts of events.
The sides are tricky. You can't really "land on" a side. Maybe if someone was really trying they could do a running leap? Probably should add some extra margin (maybe 50%?) but not as much as for the floor.
The last possibility is a person inside pressing outward. The average adult man can bench press, what, 70 kilos (about 700N? Now I can't imagine they'd be so daft to go all out trying to break the bath! But let's say a worst case *realistic* is maybe 350N. The tank should hardly notice that force compared to the 17.400 kN from the water.
Nafnlaus
01/09/2014, 03:47 PM
Hmm, one complicating factor from bracing.... bracing lets you reduce the thickness by means of reducing the amount of load on each subsection of acrylic... instead of a couple tons, it's only a fraction of that water weight. Great, except that doesn't make a physical impact from a person any less significant.
Seems to suggest that bracing needs to be either so frequent that a person can't impact the panel without having part of their force directly taken by the bracing, or so sparse that the panels have to be so strong (thick) that the impact from a person is unimportant compared to the weight of the water it's already supporting..
Again, noting that the only way a person could realistically do damage is by jumping into the water. Wonder if there's a way to effectively prevent that, either by preventing any unwanted jumping or by preventing harsh impacts somehow... hmm...
Joe0813
01/09/2014, 04:24 PM
why would you want a bath tub that you can see into? so you can see your wife/ girfriend / husband/ boyfriend naked haha?
Gorgok
01/09/2014, 04:47 PM
Entirely clear tub, partially clear tub?
Something like this?
http://www.alibaba.com/product-gs/673232560/CE_approval_clear_glass_massage_whirlpool.html?s=p
http://www.alibaba.com/product-gs/594010585/Clear_Massage_Bathtub_MT_8022.html
http://www.alibaba.com/product-gs/762076968/Freestanding_Acrylic_whirlpool_Massage_bathtub.html?s=p
Just read the first paragraph again... Concrete, epoxy to waterproof and a glass pane is what i'd recommend for a natural looking see through panel tub. Look for concrete pond builds, with viewing panels. The glass should probably have a railing on it (edges are weaker), but thicker glass is actually pretty hard to break without tools for humans... I don't imagine you will be bathing with tools. Glass can support people jumping on it with shoes on... as long as its built correctly for the load. Look up stuff on the Sears Tower.
ronman84
01/09/2014, 05:25 PM
Look, I'm not trying to kill your dream, but this is definitely not a DIY job. You would need to hire professionals for both the design and construction (Read $$$). Tanks that hold fish and tanks that hold people are worlds apart when it comes to safety and design standards because of the consequences of failure.
Imagine the consequences if your new creation is full of people and a few hundred gallons of water and something goes wrong. Just think about the liability you're taking on. If someone gets hurt or worse? Who pays for that? It will cost a lot more money than what you're planning to save by using a thinner material.
It sounds like a really cool idea, and it is totally possible... If you have deep enough pockets. But an internet forum is not going to be able to answer the kind of questions you need answered. Check into contractors who do custom designed tubs and spas, maybe even companies that do large custom aquariums too. You will also definitely need a professional engineer to design the support structure. Good Luck!
woods4542000
01/09/2014, 06:31 PM
Seems like quite the project just to be able to see thru , but to each their own. Hot tubs however have foam insulation between tub , and stand that might be a hindering factor.
pwreef
01/09/2014, 07:55 PM
Google bill wann reef tank. See if you can contact him thru one of the forums or thru YouTube. He has a 20,000 gallon concrete aquarium that he designed and built himself. Well not the concrete pouring part. Maybe he will be willing to come visit you in Iceland for a free plane ticket. :-)
Nafnlaus
01/10/2014, 04:23 PM
I'm totally up for hiring professionals - where possible.
Premade baths of course don't look at all natural, defeating the purpose.
I'll look more into glass pane - thanks. :) Glass is cheaper, too, and neither optical distortion nor curved surfaces are at play. I automatically gravitated toward plastic but glass should be a better fit. Need to find info on required thicknesses though, the calculators I've seen are only for acrylic.
Good point about windows that withstand people jumping - come to think of it, from an impact standpoint, if we just take water out of the equation, any engineer who knows how to work with glass should be able to double-check the proper thickness.
Note that the "jumping problem" only exists for the clear-bottom spa concept, not for the indoor tub concept which only requires one side clear.
Insulation isn't an issue, hot water is dirt cheap here (geothermal).
Thanks for the tip, pwreef, I'll look him up. :)
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