Question about DIY stand

hawkinsrgk · Aug 22, 2015

Hi everybody

I am in the process of building a stand for a 65 gallon tank. Tank is 48x18x17. Also the stand is being built out of 2x4 studs. I would like to leave the stand open if possible

Do I need to put a center brace on the stand or can I leave it open with a 4 ft run?

Thanks
Randy

davocean · Aug 22, 2015

I would do the top rim out of 2x6 if you want to leave it open.

redfishbluefish · Aug 22, 2015

For a four foot tank, 2x4's are just fine.....with no center brace. Anything over four foot, you need 2x6"s on the top board.

Aussie paul · Aug 22, 2015

Just run 2 cross braces on top rim to distribute weight evenly

Aussie paul · Aug 22, 2015

O

Aussie paul said:
Just run 2 cross braces on top rim to distribute weight evenly

Or even better 1/2 ply on top spreads and supports base of tank

redfishbluefish · Aug 22, 2015

Actually I'd recommend putting a 3/4 plywood top on the stand. It helps "level" the uneven-ness of the dimensional lumber.

143MPCo · Aug 22, 2015

The amount of weight a horizontal element can hold depends on the bending strength of the element and the distribution of the weight. The worst case in terms of maximum bending stress on the beam comes from a point load at the center of the span. The best case for bending comes from a pair of point loads directly located over the support brackets. A distributed load creates a lower maximum bending stress in the beam than a point load of equal total weight at the center.

Example:

A 10 foot long 2x4 carrying a uniform load of 40 pounds per foot (400 lbs total load) will have a maximum bending moment at the center of the span of 1000 ft-lbs.

The same 10 foot long 2x4 with a point load of 400 lbs at the center will experience a maximum bending moment of 500 ft-lbs.

1 gallon of RO water = 8.33 lbs
1 gallon of SG 1.027 water = 1.027 x 8.33 = 8.55lbs
8.55 x 65 gallons = 555.75lbs

As noted by @redfishbluefish 2x4 will be fine on a 65-gallon tank.

hawkinsrgk · Aug 22, 2015

Thank you for the help. The only difference between what I built and the pic from redfishbluefish is that I only have one purple 2x4 at the corners instead of two

redfishbluefish · Aug 22, 2015

hawkinsrgk said:
Thank you for the help. The only difference between what I built and the pic from redfishbluefish is that I only have one purple 2x4 at the corners instead of two

That should be just fine as long as you top it with the 3/4 plywood.....that will equally distribute load.

hawkinsrgk · Aug 22, 2015

redfishbluefish said:
That should be just fine as long as you top it with the 3/4 plywood.....that will equally distribute load.

Why do I need to put plywood on top if the tank has the plastic brace on the bottom of the tank? Only the brace will be in contact with wood. Not disagreeing just don't understand how that would help

redfishbluefish · Aug 22, 2015

Dimensional lumber is not the straightest wood, and cups, twists, warps, etc.....not to mention the slight imperfection in the joints you make in the corners. The plywood takes these imperfections out of the equation. If you were to put the plastic edge of the tank bottom on an uneven surface, you will have a point load where you have a high spot....and potentially tank failure. When you build this stand, you will see these imperfections....and the plywood "levels" these imperfections to total flatness.

hawkinsrgk · Aug 22, 2015

redfishbluefish said:
Dimensional lumber is not the straightest wood, and cups, twists, warps, etc.....not to mention the slight imperfection in the joints you make in the corners. The plywood takes these imperfections out of the equation. If you were to put the plastic edge of the tank bottom on an uneven surface, you will have a point load where you have a high spot....and potentially tank failure. When you build this stand, you will see these imperfections....and the plywood "levels" these imperfections to total flatness.

Ok. Got it. Thank you so much for your help.

Windy · Aug 23, 2015

Especially if you use construction adhesive to apply the top. It will fill low spots.

hawkinsrgk · Aug 23, 2015

Windy said:
Especially if you use construction adhesive to apply the top. It will fill low spots.

Thanks Windy

Never heard of that. Will look for it next trip to lowes

don_chuwish · Aug 28, 2015

Yeah the common "DIY" stand plan example above is great - indestructible if assembled well. But it's also gross overkill - especially the 3 2x4s at every corner. A 3' tall 2x4 has a 'column' strength over 4000lbs when unsupported.
Play around with this for fun:
https://courses.cit.cornell.edu/arch264/calculators/example7.1/index.html

What the design above does nicely is brace against racking - necessary assuming there is no 'skin' over the stand.
If you are (like me) skinning a stand with plywood that creates the 'diaphram' effect required to prevent racking - like a stud built house with plywood or OSB sheeting on the walls. That sheeting adds even more vertical compression strength as well.

hawkinsrgk · Aug 28, 2015

Thank you don_chuwish for the explanation. The main thing I was concerned with was if I could get away with not having a center support. My stand is pretty much like the one above except I have 2 (2x4) on each corner instead of 3. I dont plan to skin the front or back of the stand. I am planning to use plywood on the sides, however its not really that thick..... maybe 3/8 or 1/2. The stand is 3 ft tall. I had no idea a 2x4 was that strong.

Thanks again
Randy