Tank stand

[daleros]

Is this flexing bad in the long run? Cause the tank is set up already. When I rock the stand it doesnt seem to be flexing. But can I leave it the way it is? What other cheap methods are there to fix it?

It fatigues the joints. It is like bending a paper clip back and forth several times. It is hard to determine when it will break. The welds probably won't fail without a huge impact. What might be bad -- If you have a large glass tank and things get too out of square the glass might get overstressed and fracture.

If, might, it is hard to tell without a picture.
You could put in some cross bracing with the tank in place. Just drill the angle iron and use bar stock and bolts. If it is already finished that might be a problem.

Here is another example. When a home wall is build the 2' X 4' wall can rack before rest of the timbers are in place. To prevent this most builders use plywood at the ends of the wall nailed to each stud and the top plates. Some builders use plywood on the entire wall which is a little overkill structurally.

If the stand is finished, you could try to put more attachments from the sheeting into the angles.

 

[JayK1320]

you could bolt in some cross bracing like daleros was talking about. If you welded in some more cross supports and x-bracing you should be fine. I would be, same as daleros, its due to joint flex or possibly if the pieces of angle are long enough they can bow under weight, and it doesnt take much to get a little wiggle. Based on your description I dont think it would be something to worry about, but some pictures of the stand would help. if you cant weld the bracing in, you could bolt it, you would just have to do it in a way to make sure everything had two bolts so that their is a rigid joint. Again, a few shots of your stand I think would make it easier to describe and see exactly what you got. Angle is real sturdy, what size did you use? 2x2 or 1x1?

 

[Ja1983]

the problem that is ocurring is the natural tendancy of the steel to flex, it will flex more over the longer span than a short span.. while it may well be sufficient to support the weight, it will deflect under that weight to a certain extent. this is where your problem is:

if even pressure is not applied to the base (i.e if its slightly twisting, or like you said, if one corner is lifting) then this puts stress on the glass... because its trying to bend under weight where there is no reaction to support it.

you need to minimise the flex in the structure.

EXAMPLE:

take a 12" ruler.. support it at both ends.

now press in the middle - it deflects really easily

niw support it at an end, and half way - it is much stronger, and doesnt bend as much.. think of the ruler as the longer sections of the frame.

by putting bracing in you are reducing the span between supports, and therfore reducing the deflection.

if you are bolting your stays/struts, drill the holes a quarter of the way in from the end (this is where the shear force/bending stress is at its lowest) and take the bottom of the stay to a few inches from the bottom end.. as the forces are fairly even due to it resting on the floor (the bottom acts in tension, as a tie to stop the legs spreading ) the bottom rails also spread the load over the floor to prevent the tank sinking into your floor!

not sure how this will look, but i`ll try a diagram!

____________
| / \ / \ |
--------------

this then makes your longest length (top rail) effectively a third the length, as load is transferred to the bottom rail via the struts.

i`m sorry if that doesnt read too well, as i`m trying to keep it simple, but accurate... and i`m useless with words!

heres a model of mine. Note theres no x bracing - mine will be clad with 12mm ply, with 18mm ply over the top. there will also be a sheet in the middle, so it will be braced in all directions.
click for the bigger picture!

 

[daleros]

If it is a material flex problem more vertical bracing helps. I doubt that from what you have described the angle iron is flexing.

It sounds like a racking problem. The square sections wanting to be pushed out of shape and putting stress on the welds.

 

[daleros]

http://en.wikipedia.org/wiki/Truss

The stand in the post above is an example of an Vierendeel truss. It is very strong for vertical loads (the tank pushing down on the stand) but is very weak for for lateral loads (the rocking of the stand under weight) When these trusses are used they have reinforced joints. A wood stand should have metal plates at the joints and not just nails.

You basically have a Vierendeel truss without reinforced joints. If you post a picture I can show you how to turn it into a King Post truss to prevent the racking. Or, just don't bump the stand if it isn't too bad.

 

[12 Volt Man]

hmm.. the LFS's around my area carry lots of metal stands that supposedly handle the weight better than the pine stands/particle board stands from Perfecto/all-glass.

I have had all my tanks set up with them for over 16 years.. I have a 90 and a 65 on one stand, among other tanks.

there has not been any flex to the stands, they are rigid as hell.

is an angle iron stand like these ones:?

 

[daleros]

Those tube stands are really good. Square tubing usually has a better joint construction compared to angle iron. Also, if I understand his situation, he doesn't have the bottom shelf either. But those square tubing stands still have all the stress on the joints. They are just made strong enough to handle it.

 

[Fiaman]

@ 12 volt man, yes but its made from 5x2 angle iron. And it does have a bottom shelf for a 65gal sump. Ill will try to get pics

 

[Fiaman]

Actually its 3x2's

 

[Jackd]

On the older angle iron stand they used to weld a 1/2 inch piece of squre tubing along the inside middle of the stand to help with the flex. Depending on the thickness of the angle this might be unnecessary and it might just be the floor. Something to consider if you ever empty the tank and have the stand free to work on.