300 gallon stand question

[jccaclimber]

I'm getting ready to make a stand for a 300 I am buffing out. Tank is 96x24x30. Top of the stand will be 4x 2x4s with 3/4 plywood on the top and bottom of those (almost like a torsion table). One 4x4 in each corner, a 2x4 (maybe 2x6) rim around the bottom, and a diagonal or two in the back, possibly one on the side. I do not want a center support column for a variety of reasons.

The questions I have:
I'm in a nearly 95 year old house and I know my floor isn't level (still figuring out how much). It's entirely possible that there is a full inch drop from the back right corner to the front left corner. The floor is wood, and leveling it in advance is not an option. I'll be adding a couple columns under the tank before I fill it, so I'm not worried about much movement after I get it set up. Do I:
1) Make the stand for that location, understanding that it isn't going to be square.
2) Make it square, and shim it to level (Don't want to dent the floor at the shim locations though).
3) Deal with it being off level.
4) Other (suggest).

I do plan to skin the frame with something like 1/4" ply with a nicer veneer, but I may be able to hide some difference in height with the top and bottom trim.

Also, any thoughts about the bottom rectangle of the frame being 2x4 vs 2x6?

 

[DayumDanny]

you can add a nice piece of plywood under the tank that has an area larger than your tank stand. It can serve as your base so that when you go to shim it, it wont dent the floor and since the area is larger than your tank if you ever do water changes or do anything to the tank water wont directly fall onto your wood floor but on the plywood instead.

 

[jccaclimber]

To make sure I'm understanding this: Floor>Plywood>Shim>4x4 leg. How thick do you think the plywood needs to be to sufficiently distribute the 700-800 pounds I'm planning on having on each leg? Following that, suggestions on hiding the fact that one end isn't touching the floor?

 

[David R]

You're right, the plywood won't be anywhere near rigid enough to distribute the load on the floor. It may stop denting if you have hardwood floors though.

Is the tank 30" tall or wide? Either way you're a brave man! I saw a picture somewhere showing how someone had made their own adjustable stand using timbers, large washers and bolts, I think something like that would be your best bet. If it were me I'd be going for a steel stand with threaded industrial feet that sit on another steel frame that spreads the weight onto the floor, but with a bit of clever planning you could probably build something similar with timber.

IMO you would want something more rigid that 2x4 for your 96" span too. Is the tank glass or acrylic?

 

[rbarn]

I'm getting ready to make a stand for a 300 I am buffing out. Tank is 96x24x30. Top of the stand will be 4x 2x4s with 3/4 plywood on the top and bottom of those (almost like a torsion table). One 4x4 in each corner, a 2x4 (maybe 2x6) rim around the bottom, and a diagonal or two in the back, possibly one on the side. I do not want a center support column for a variety of reasons.

Also, any thoughts about the bottom rectangle of the frame being 2x4 vs 2x6?

This is not strong enough. You need to reinforce the span with steel. Even then I would still want a center post. This thing is going to weigh as much as a small car when full.
I would seriously consider hiring an engineer to look at your floors too. You're going to have over 2,000 lbs sitting there.

For what you want I would call a welder and make it out of steel. He can put industrial strength screw leveling feet in each corner and make it a snap to get level.

My 96 x 24 x 30 - 300 gallon stand - thats a doubled up 2X10 spanning my door openings and I still ended up adding the center brace to be safe.
2X6 studs every 16-18" for support and wrapped in plywood to tie it all together.

 

[aldiaz33]

I think an unsupported span of 8' using 2x4s or 2x6's is going to have quite a bit of deflection. Even with steel stands (assuming you aren't using an I beam) in most cases you want a vertical support at least every 30" or so. You should try to make it symmetrical (I don't like the idea of cross bracing the back or sides only). If it's not symmetrical all that weight is going to be acting differently on the stand which could lead to problems. I would use two 2x4's over a 4x4 in the corners...4x4s are more likely to twist over time and at a bare minium, two vertical supports between the legs.

You are probably looking at closer to 3,000lbs when you factor in water, tank weight, substrate, etc.

My floors were off-level by 1.25" over the 10' span of my tank, sloping down right to left. I had to get it level in order for my overflows to work properly (if I set it up as is, one of my overflow towers wouldn't have been drawing any water at all). Regardless of whether or not you have overflows though, I think leveling the tank is a good idea.

I have yet to see a great solution for someone setting up a big tank on hardwood floors that they are concerned about damaging, so I can't help there.

Below are some pix of what I had to do to get my big shims under the tank. I made the shims out of various thicknesses planks of wood that I glued together and I just used a heavy grit sandpaper to smooth the transition from one thickness to the other. I only had an orbit sander, but using a belt sander would have made the process a lot easier/faster.

Good luck!

 

[jccaclimber]

The tank is 24" front to back, 30" tall and made of 3/4" acrylic. This will also be set up in my garage for a bit while I'm finishing some things in my house so if it's grossly underbuilt I'll find out in a safer place. As stated above, two columns will be installed in the basement directly under the tank. It is also perpendicular to the floor joists, and along a supporting wall. I'm not sure yet if I want to pour footers or use some spare 15" steel channel that I have to distribute the load from the footers, but it will be solid.

I've attached below a cross section of what I'm planning for the top. The legs are gray, plywood is green, and the 2x4s are blue. Naturally there will be a sufficient amount of screws (and likely glue) between these for them to act as a single component. For those doubting that this will hold, below are some of my calculations. I don't want to come across as not listening, but I didn't just make this up and I'm confident in the design for the top of the stand. If you see holes in this, do please point them out to me. I'd rather find an error here than put a tank through the floor.

Assuming the same material (wood) for all of the following options, area moment of inertia is the main determining factor. Here are the values for what I'm planning, as well as some things that have been suggested:
2x4 and 3/4" plywood layout below - 186 in^4
Two 2x8s - 95 in^4
Four 2x8s - 191 in^4
Two 2x10s - 198 in^4

If you trust this to two 2x10s or four 2x8s then this setup isn't far off.

Assuming a 3,000 pound load (within what I specified above for leg loading) and an 86" unsupported span (inside to inside on the legs), the safety factor using pine is right around 13. Obviously the load isn't always dead vertical and static, but that's also a substantial safety factor. I'm expecting around a tenth of an inch deflection new, and a bit more due to creep over time but I'm planning a foam sheet over the top plate to cover for that.

For another comparison, deflection and safety factor are better with the wooden section below than a span made of 1/4" wall 3x3" steel square tube (ASTM A500 or A513).

I've thought about screw jacks in the middle of the legs, but I'm more comfortable leaving them solid, even if I do need to make them each a different length. I don't want screw jacks on the bottom as I'd rather not dent my wood floor.

Aldiaz,
For some reason I can't see your pictures in post, although they work if I open them in a new tab. I was considering a similar method with a 12 ton bottle jack if I need to adjust it after build (drained 90% of course). Your shimming method looks reasonable, and I may resort to that if I have to. I think it would be easier in my case to separate the 4x4 from the bottom frame, shim just the leg, then reattach the leg to the frame. I'm hoping if I need to do that that I can drop the bottom trim in one corner to hide the gap. I had to shim a friend's counter in a very similar manner to what you did in order to keep water from puddling in the front of his counter and corner of his kitchen sink. He's in a rental, so everything we do needs to be completely reversible for when he moves out.

 

[David R]

I'm not sure I "get" your calculations, are you saying that the ply/4x2 box you're making will be as strong or similar to 2 10x2 or 4 8x2? If so, then you're probably right, I'm not doubting you, but I still think an 86" unsupported span is a big ask. I know glass and acrylic tanks have slightly different needs, and I am only experienced with glass tanks where 0.25mm flex in the stand is enough to transfer most of the force onto the glass and silicone. For the 1100mm front-to-back span of my 2000L tank (which is only 700mm high, 62mm less than yours) I used 100x50x5mm RHS. Anything longer I would have gone heavier again, I wouldn't use 75x75x3mm (or 3x3") for anything much over 600mm unsupported. As I said, I'm not sure if acrylic tanks are a little more tolerant of flex in the supporting members, but I certainly wouldn't want to experiment with that much water in my own home.

 

[Drstrangelove]

http://www.woodbin.com/calcs/sagulator.htm

I tried plugging some numbers in here. When I did, it came out to a lot more than .1" deflection.

I'm not sure how this is going to work. 3/4" plywood is used as flooring and it's given far more support than this seems to have to me (typically 2x6" 16 inch on center spanning to support structures like I-beams or poured concrete walls.)

I'm sure I am not understanding this but is acrylic that strong?

 

[jccaclimber]

^I haven't used the woodbin calculator before, but I can't configure my setup above in it, namely due to the second sheet of plywood. The second sheet is what makes this work. I've assumed E=1.3x10^6 psi for stiffness, and δ = 5 q L[SUP]4[/SUP] / E I 384 for deflection.