Attention! Structural engineers!! Aquarium stands!

[jagermeister]

A lot of us are trying to build our own stands for our aquariums. I've seen everything from building the frame out of 4x4's for a 90 gallon (extreme overkill) to frames of 2x4's to the pet shop models of what looks like 1x4's stapled together.
My question is this. Is there a web site that anyone knows of where we can go to to look up maximum loads on various types of wood elements?
For instance, I'd like to know the maximum lbs/in that a 2x4 made out of pine can support with a 4 foot span. Obviously the critical point will be in the center of the span.
Maybe someone wants to build a stand 4' in length without using a center brace. Can a 2x4 handle this or would you have to move up to a 2x6 or 2x8.
Just curious if anyone knows of a site that would help in finding answers to questions such as these.
Thanks.

 

[sm_in_la]

I'd like this info as well. I'm in the process of thinking up a structural design for a 90 gallon.
Thanks.

 

[fulcrum]

Check out this site:
http://www.woodbin.com/ref/wood/strength_table.htm
It should help. Also note that with proper construction techniques you can achieve a much stronger structure with much less wood. There is something to be said for having a carpenter's help.

 

[beaslbob]

Originally posted by jagermeister
A lot of us are trying to build our own stands for our aquariums. I've seen everything from building the frame out of 4x4's for a 90 gallon (extreme overkill) to frames of 2x4's to the pet shop models of what looks like 1x4's stapled together.
...
For instance, I'd like to know the maximum lbs/in that a 2x4 made out of pine can support with a 4 foot span. Obviously the critical point will be in the center of the span.
...
Just curious if anyone knows of a site that would help in finding answers to questions such as these.
Thanks.
Maybe someone with stand building experience can help here. The site posted above is excellent but I wonder how many of us really understand such properties as bending moduals!
I think one of the primary concerns is settling of the tank over long periods of time.
My gut feel is that the major weakness would be the joints not the actual wood members. Additionally, the cost of 2x4's is not the major expense. Therefore, I think you should pay very close attention to the joints and use as many diagonals, fillets, and gussets as you can.
Of course, you must make sure the tank does not tip over and the weight is spread over the maximum area possible.
That said, the only stand I ever build was for 2 10g's, 1 5g and 1 20 g. Not too pretty but is lasted for years.

 

[dreeves]

What size tank is it with the 4' span? And also...is it going to be an open base stand or enclosed?

 

[me-n-my-fish]

I have built numours (sp) stands. from anywhere to a 260 gal to a 10 gallon. Like beaslbob said, pay close attn to the joints. I all ways use big heavy lag bolts. I build two 2x4 frames, that is the size of the tank. One for the top, and one for the bottom. The more of the stand that is incontact with the ground the less pressure that will be applied to one certain area. I frame that in with 2X4's. Make sure it is square. a 2x4, square up and down, will take a lot, like coupla 1000 pounds of force (from top to bottom) before it goes.
Another thing you MUST think about is the center of mass. In your tanks, if you find the center (kinda in your head), move down just a little, this is the center of mass. All the wait is there. Now visualize a string coming down from your center of mass to the floor. Once again in your head, the tank moves from side to side. At any time when the center of mass is not over the stand, it will come to the ground. So watch the height. If you want it to be high, then build a wider base. Dont want a real wide base, build it lower to the ground.
Just MIO

 

[bridge man]

Mr. Jagermeister,
This is the answer (w/ slight modifications) I gave to your question on reefcentral. I can't remember if it was you that posted it, but the question was the exact same.
"According to ASD Structural Lumber Supplement, a No. 2 southern pine 2x4 in bending can handle ~4590 lb-in of moment. Assuming an even distribution of load across the 48"- 2x4, this equates to ~16 pounds per inch. A 90 gallon, of 20" tall x 18" depth gives ~13 pounds per inch. You would have two 2x4's running the length of the tank (one in front & one in back), therefore each would only see 6.5 pounds per inch, which is about 40% of their capacity. Plus, you have to remember, that the vertical pains of glass really aren't bending vertically along the length of the tank. This means that the horizontal 2x4's really aren't seeing an evenly distributed load across their length, but rather the load is concentrated on the ends, where the corner posts are located. Therefore, 2x4 horizontal members are adequate. For corner posts, a No. 2 southern pine 2x4 at 4' long can carry 7080 lbs, while a 6' long post can handle 4780 lbs. These vertical member values are for wall studs, which are braced with plywood against bending about their weak axis. As you can see, one 2x4 could hold the weight of the tank, but obviously four will be used."
As someone already mentioned, beef up the connections, and you should be fine. A tank held up with 2x4's doesn't look safe, eventhough it may be. Your best bet is to build a stand that looks like it will hold, that way you will have some personnal reassurance that nothing will fail. And be sure to brace the stand against swaying front to back and along the length of the tank.
Hope this helped,
Bridge Man

 

[jagermeister]

Thanks for the replies. For the joints I'm thinking about using those prefab metal joint connectors used in decking.
Also, what kind of finish wood and how to attach it? I want to use oak and noticed a sheet of 3/4" oak plywood runs about $50. Cheaper alternatives?
What's the best way to attach the finish wood to the 2x4 frame? Is there a way to do this to minimize the number of screws you see on the outside? Can you attach it from the inside of the frame somehow?
Thanks for the help!

 

[bridge man]

You could screw through the 2x4's from the inside with 2" screws and not penetrate the outside of the plywood. 2x4's are really 1.5x3.5, which means a 1.5" stud plus 3/4" plywood gives you 2.25". A 2" screw would give you 0.5" of embedment into the plywood while leaving 0.25" of plywood on top, thus eliminating any screw from being seen from the outside.
That would work for screwing into the this side of the 2x4. For the wider side, a small screw block of some sort can be screwed flush to the outside face of the 2x4, then the plywood can be attached through the screw block. Hopefully, you can picture what I am talking about.
Bridge Man

 

[jagermeister]

Thanks Bridge Man,
That was me who posted on the other site. Thanks for the reply!
I can totally picture what you're talking about. Thanks again!
Are you a structural engineer? I had a structures class way back in college and was actually trying to figure out beam deflection and max. moments for a 2x4. I couldn't remember how to calc. the moments of inertia or where to go to look up modulus of elasticity and that stuff so I thought I'd just ask. Plus I didn't know where to go to find max. bending moments or shear stresses for woods of different cross sectional shapes.
Much easier to ask and find someone who's up to date on all that stuff. Plus I know just enough about structures to be really dangerous.
Thanks again!

 

[bridge man]

I am a civil engineer, but I guess I could be called a structural engineer. My degree is in civil with a heavy, and I mean heavy emphasis on structures. I actually design bridges and other highway structures, hence the name "bridge man." I had a wood design course in college, so I am pretty well up on the stuff, plus we design wood members on occasion for the different places it is used during construction of highway structures.
All that talk about modulus of this and moment of that makes me shiver. That stuff just confuses the design and designers. Wood is allowable stress design (maybe you've heard of it), so you really don't need all the material properties, just an allowable stress that the different types of wood can handle under different loading conditions.
Glad to be of assistance,
Bridge Man

 

[sebae0]

bridgeman already said it but if you ever had a 6' tank on a angle iron stand you will notice that the center of the tank and some distance each way is not even in contact with the metal. all of the weight is actually supported on the 4 corners. i had a 130 on a metal stand for years and the gap in the center is high enough to fit a piece of airline tubing thru it with no resistence.

 

[chef jaysen]

me n my fish do you have any pics or diagrams for the stands you have built for any thing around 220 or so. I am going to build a stand for something in that size to put in the wall. Any ideas out there would be greatly appreciated. Thanks

 

[sacker8472]

Jager,
I would shop around for sheets of plywood. Depending on what area of the country you live in, you can often find full-scale lumber yards that will sell retail. If you are up for it, you could also try to veneer birch plywood, which is only about $30 per sheet at HD or Lowes.
Regarding the manner of construction, I use a mortise and tenon joint secured with lag screws or pegs. IMO it is much stronger. For purposes of attaching the plywood to the base, I would look at a few of the basic woodworking books, especially ones on building kitchen cabinets. This book will also cover door construction, hinge options and placement and probably give you many other tips you can use.

 

[me-n-my-fish]

I dont have any pics of the 260 stand i made. Butt hole never paid me back for the wood that i used, (that was the only thing i wanted! So, we are kinda on the outs right now.
But, anywho's, drop me a line, and we can talk, and i am sure we can come up with a good design. I will post some pics of the other stands that i have.
chiefrigger@reefriggers.com
me-n-my-fish