Stand design discussion

[jccaclimber]

I'm looking to make a stand for a large (126"l x 34"d x 32"h) glass tank, with the goal of maximizing the open space between legs. When asking around about support I either hear "Put a vertical every 2 feet" or "It must be uniformly supported" (case A).

I believe proper design can get around putting a vertical every 2 feet, and "uniformly supported" is an awfully vague statement. I'm looking for some guidance on what is actually needed.

Let's start this with the RocketEngineer stand here:
http://reefcentral.com/forums/showthread.php?t=1169964

I'm choosing that because there are a lot of them out there, and because they happen to be really easy to make. If you ignore the beams going front to back (is this an acceptable simplification?*) it's a beam, supported at each end.

Let's assume a 75 gallon tank weighs 700 lbf. Spread it across two 2x4's with a 41" span between the legs. If you apply a uniform load to a beam, the center bends down (case B). In this case I'm coming up with ~0.030" deflection at the center of the stand*.

Doing the same for a 6' 125 gallon tank weighing 1100 lbf I come up with 0.055" deflection at the center of the 65" free span.



My first two thoughts are:
1) The tank doesn't bend this much (or does it?), so the center is actually less supported than the ends (case C, what I think actually happens).
2) A 6' 2x6 isn't straight to within 0.055" to begin with. Additionally if the legs aren't equal length the frame will twist to meet the floor so once more, the tank isn't "perfectly" uniformly supported.

As additional evidence consider the stand for my 8' 300 gallon. It has legs at each corner (86" open span). The top is 1.5" of plywood on each side of 4 vertical 2x4's (total height 1.5+3.5+1.5=6.5") with a sheet of styrofoam between the tank and stand.

Uniformly loaded it would deflect 0.045" at mid span. I haven't tried to measure deflection since the first fill years ago, although it was about the expected amount then. I know that it deflects, but I also know the stand carries a higher share of weight at the ends than the center. I made the stand with a very slight rise in the center, so when the tank is empty you can slip a sheet of paper freely between the tank and stand at the ends. With the tank full this reverses, the ends are loaded (and the foam compressed slightly), but I can slip a business card between the foam and stand at the center with only slight drag.

My question: What sort of support should I actually be going for here?


*1) I also know that many aquariums are edge supported. In my case they glass ones don't have a frame and the 8' tank is acrylic, so they are all supported along the entire surface rather than just at the edges making my 2d simplification at least slightly more appropriate.
*2) I am using 1.5e6 psi for Young's modulus of wood.

 

[ericarenee]

If i were going to build a Free standing tank stand for a 8 foot long tank and i want to keep the entire front as open as i can ..

I would build a 3 sided 3/4 inch Plywood box prob hardwood veneer outer finish.

Build two Frames one out of 2x4 for the sump area . This will span the whole inside of the stand..
Build a box for the top as well but use a laminated 2x8 for the front..

 

[jccaclimber]

I am making a stand for a 10.5 foot tank, the 8 footer has been up for a couple years now. I could mostly close the back and one end, although that is only a two sided box. I'll be making a veneer face to go over at some point, but right it needs to be removable. It seems like every couple years I decide to rearrange some aspect of the sump in a way is easier to do out of the stand. The open center makes this a lot easier. I need the other end open, or at least a very large removable panel as I am planning to put a small refrigerator and freezer at the end.

Also, not stated above but there will be appropriate gussets and diagonals to prevent the stand from twisting or tilting over.

 

[Fuel Doodle]

I am making a stand for a 10.5 foot tank, the 8 footer has been up for a couple years now. I could mostly close the back and one end, although that is only a two sided box. I'll be making a veneer face to go over at some point, but right it needs to be removable. It seems like every couple years I decide to rearrange some aspect of the sump in a way is easier to do out of the stand. The open center makes this a lot easier. I need the other end open, or at least a very large removable panel as I am planning to put a small refrigerator and freezer at the end.

Also, not stated above but there will be appropriate gussets and diagonals to prevent the stand from twisting or tilting over.

If you want a large stand with an open front, look to make your stand out of metal instead of wood. the metal will be much, much stronger.

 

[BlueRoofTang]

I'm in for other comments, but correct me if I'm wrong...

but isn't the entire weight of the tank going to wind up on silicone anyway, giving it some ability to distribute weight over a surface that's not perfectly flat? That is unless there is no plastic frame around the bottom..

 

[jccaclimber]

I'm in for other comments, but correct me if I'm wrong...

but isn't the entire weight of the tank going to wind up on silicone anyway, giving it some ability to distribute weight over a surface that's not perfectly flat? That is unless there is no plastic frame around the bottom..

For plastic framed tanks I suspect that is correct, but in my case there is no frame. The 8' 300 is acrylic, walls sitting on bottom. The 170 is 1/4" of a hard plastic siliconed to a 1" sheet of glass, and the walls built on top of that.

The new 580/590 is glass with a floating bottom pane, but the bottom is flush with the walls, and being 30+ inches across I assume it should be supported across the center in some manner.

 

[skiingfast]

Here are two suggestions.

Use 2x6s. Put one laying flat that the tank will rest on and then two under it on their sides, lined up with the side of the flat one. This will form a U shaped channel. Support the ends with post made up of three 2x6s that are under all or the horizontal pieces. I suggest this because look at the biggest window in your house, they are built like that so the load goes across them not into the window.

You could also try a glue laminated beam likely more expensive.

Plan c. Make an arch. Use plywood and that is the height desired. Cut the opening, leave the ends thick. Then curve up to the top leaving a good 6 inches across and curve down likewise at the other end.

 

[GQsmooth]

You might be able to get away with 2x8's as your frame, but that's even sketchy without a centre brace.

Personally, I would get a metal frame built for that size tank.

 

[jccaclimber]

At this point I'd say the odds are 80% that I'm going to go steel rather than wood, but that isn't the question. I can make it out of steel, wood, carbon fiber, or anything else, but it still comes down to designing it for a given strength (easy) and stiffness (harder) under load.

Making this thing won't be a problem, and designing it won't be much of an issue either. Determining what spec. I need to design it to is the part that is giving me grief.

 

[ericarenee]

At this point I'd say the odds are 80% that I'm going to go steel rather than wood, but that isn't the question. I can make it out of steel, wood, carbon fiber, or anything else, but it still comes down to designing it for a given strength (easy) and stiffness (harder) under load.

Making this thing won't be a problem, and designing it won't be much of an issue either. Determining what spec. I need to design it to is the part that is giving me grief.

Before you design it you need to know the materials you wish to use.. For that span and to get the space you want
Steel or Lam beam is your only two options.. Or FOR A 10 ft span what we done before lam beams.. Take two 2x6 and a piece of 3/8 inch flat steel and sandwich the steel between the 2x6 drilling holes every 2 feet for 1/2 in thru bolts Alternating from 2 inches down to 2 inches up ..

ohh by the way I am a Contractor . Not that that matters on the internet..
For gaining the max space steel is the way to go.. but will be MUCH More expensive as you will have to use tube steel to get that length with no deflection..


My tank has the 2x6 with steel plate totally unsupported on the front except on each end.. the weight is carried to blocking between the floor joist carried to jacks from basement floor to blocking.. THIS is also something you have to consider putting all the weight in the for left and right on the floor instead of it being carried across the whole length...

 

[skiingfast]

I want to mention something.

Putting a brace across the middle is not needed.

While long tanks have those center braces that because the water is a liquid that applies it's pressure out to the sides. That causes a tank to bow out so the brace resists that.

However since your tanks frame sits on the stand, all the tank's weight is pushing down. It won't make the stand bow out.

 

[ericarenee]

I want to mention something.

Putting a brace across the middle is not needed.

While long tanks have those center braces that because the water is a liquid that applies it's pressure out to the sides. That causes a tank to bow out so the brace resists that.

However since your tanks frame sits on the stand, all the tank's weight is pushing down. It won't make the stand bow out.

Incorrect (Called Bridging ) Actually helps support the weight by toeing the whole structure together, Wight pushing straight down on 2x lumber or Steel will also by nature twist the members.. the bridging keeping this twisting from happening puts all the force straight down and there does in fact keep it from bowing....

 

[jccaclimber]

Before you design it you need to know the materials you wish to use..

I can design it either way, what I need to know is what deflection to design to. Once I have that I'll design one in steel, one in wood, maybe one hybrid, tally up the costs and make up my mind.

For that span and to get the space you want
Steel or Lam beam is your only two options.. Or FOR A 10 ft span what we done before lam beams.. Take two 2x6 and a piece of 3/8 inch flat steel and sandwich the steel between the 2x6 drilling holes every 2 feet for 1/2 in thru bolts Alternating from 2 inches down to 2 inches up ..

Unsure on the 10 ft span, but sure on wanting 4 legs. Having the ends open won't be as good as the wider gap in the center, but is better than say 6 or 8 legs. I have access out one end, but that starts to interfere with the base of a stairwell after a few feet. I can get an 8' object in if I can rotate it out a bit after the first couple feet, and not having a support in that corner gets me that.

ohh by the way I am a Contractor . Not that that matters on the internet..

Did you make the stand surround in your avatar? It looks very nice.
Card carrying (literally) engineer here, although obviously I still need some help.

For gaining the max space steel is the way to go.. but will be MUCH More expensive as you will have to use tube steel to get that length with no deflection..

If I go steel it will be a giant box section like the top of the wood stand I built for my 300. The material is only a few hundred dollars. It actually doesn't change price or weight much with additional stiffness if I'm just making it thicker, but I do have to give up some clearance height underneath.

My tank has the 2x6 with steel plate totally unsupported on the front except on each end.. the weight is carried to blocking between the floor joist carried to jacks from basement floor to blocking.. THIS is also something you have to consider putting all the weight in the for left and right on the floor instead of it being carried across the whole length...

Sounds like what I had to do for the 300 at my last house. Support the floor with 2x10's followed by steel columns followed by 24"x24"x6" laminated wood blocks. The floor in that basement was nothing but a skimcoat of cement, but fortunately the fill under it was both dry and solid.

In my current house the first floor where the tank will be is a slab. I haven't drilled a core sample, but the exposed edge of the slab at the outside of the house just a few feet away is oddly enough 10 inches thick. The tensioning cable there is about halfway down, so I don't think they would have suddenly thinned it out, although that's a guess on my part. I've put heavier machinery with a smaller footprint on thinner slabs with no issue, so I don't think floor loading will be a problem.


Right now I'm thinking two sheets of 11 ga steel separated by something like 2"x4" rectangle tube, but I'm debating if I can get away with smaller tube, although if I get too much smaller I'll be drilling holes for welds as my arm only fits in so small a hole. What I can get away with of course depends on that all magical allowable deflection number I'm trying to determine.

Making a 6" version with a couple sheets of laminated plywood top and bottom, separated by 2x6 (or whatever) boards also comes to mind. At most a few hundred $ in materials plus some time and I've got a steel stand, less if I go with wood.

Two legs on 70" centers and a 28" overhang at each end allows the thinnest platform. I should probably run it through ANSYS and compare to my hand calcs.

 

[ericarenee]

With the tube steel do not just compare the exterior dimensions thickness of the steel and quality and type. Red iron for example is very strong but has a higher selection them some other tempered type of steels but they are more brittle . I am not a expert on the types . i always just went with what the engineer give me on plans .

For instant a bed frame is made of tempered steel. its very hard to bend but once it starts to bed it will weaken and break at one spot .

anyway

Yes i built the stand in my avatar the back of the tank actually sits on a double 2x4 plumbing wall . there is a bathroom behind the tank. So on half of the back of the tank i can access the plumbing and over flow to basement with doors that are behind the bathroom door..
You cant see by images but under the tank. is a 4 foot 90 gal fuge... so its totally open ..


Cant wait to see what you come up with i will follow along. if you have google plus you can search on there for DIY Reef Aquarium forum and find my stuff.. not trying to push my community.

Good Luck

 

[jccaclimber]

With the tube steel do not just compare the exterior dimensions thickness of the steel and quality and type. Red iron for example is very strong but has a higher selection them some other tempered type of steels but they are more brittle . I am not a expert on the types . i always just went with what the engineer give me on plans .

For instant a bed frame is made of tempered steel. its very hard to bend but once it starts to bed it will weaken and break at one spot .

I'll be designing to whatever the structural steel supplier has available. I'm guessing A36, but it won't be a big deal either way. That is a good point for people following along though. Some of my widgets at work are made of mild steel, others heat treated A2, some powder of various compositions, others stainless. Saying "steel" is about as specific as saying "coral". Fortunately the density and stiffness doesn't vary that much, and the cheap structural alloys are fairly standardized.

anyway

Yes i built the stand in my avatar the back of the tank actually sits on a double 2x4 plumbing wall . there is a bathroom behind the tank. So on half of the back of the tank i can access the plumbing and over flow to basement with doors that are behind the bathroom door..
You cant see by images but under the tank. is a 4 foot 90 gal fuge... so its totally open ..


Cant wait to see what you come up with i will follow along. if you have google plus you can search on there for DIY Reef Aquarium forum and find my stuff.. not trying to push my community.

Good Luck