Large Tank Design Help

[ceophd]

Hello everyone,

I could really use some help. I am planning to build a 120x48x30 with a 12in Euro. The plan right now uses 0.75 inch acrylic (0.708in) throughout. And the waterline will be at 28in.

The displacements seem fine.

0.112in < L/480 = 0.25
0.079in < L/480 = 0.10

The question I have is with the stresses. What is the allowable stress that designers use? I was only able to find one source during my research and it suggested to use values between 1/10 and 1/15 of the acrylic's strength. The numbers that I have found are as follows:

Tensile Strength-10,500 psi 1/15 = 700 psi
Flexural Strength-16,000 psi 1/15 = 1070 psi
Compressive Strength-18,000 psi 1/15 = 1200 psi

I ended up with a max tension stress of just under 700 psi and an equivalent stress of 595 psi.

I have built several small tanks and this will be my first large one. Any advice would be extremely helpful. Thanks.

I have attached the plots below.

 

[ReefingBuddha]

I would go as thick as you can. I decided to go with 1" glass on my 5' x 5'x 30" tank and am looking forward to the peace of mind it will offer. I am no engineer but from what I have heard the resounding idea is to go as thick as possible. Sounds like its going to be a hell of a tank. Enjoy

 

[Acrylics]

1500 is considered by many as maximum allowable, it's the number given by many mfrs but I don't like it one bit. IMO 750 should be maximum allowable for pressure vessels of this sort and prefer a bit less. IMO (again), 18mm (.708") is a bit thin for this though within limits, I would use 1" material.
Using 1" and the 2 (8-12") crossbraces, you should be able to cut the eurobrace down to 6" with lower overall deflection rates. I would however recommend that you change your top though to a single sheet with larger radii in the corners of the access cutouts to distribute stresses better if you are going to do this. A 2-3" radius will help great deal.

HTH,
James