acrylic load calculator?

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actionplant

Feeder Fish
MFK Member
Oct 23, 2007
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Bismarck ND
It would be fantastic to see a spreadsheet of water load differences at different depths, much like the glass thickness guide. I'm wanting to build a tank but am seeing conflicting information.

Also, I'm assuming Lexan is stronger than cast acrylic, I wonder how much better it can handle loads at different thicknesses?

Just as an example, if a person were building an 8' wide tank, a standard pre-cut sheet size is 8'x4'. Assuming a plywood/fibreglass tank, braced at the top, are we talking any real difference in thickness per inch of height of lexan over cast acrylic? And how much greater might the load be at 48" vs. 30"?

FWIW I highly doubt I could manage a 4' deep tank right now, this is just for the sake of argument.

Assume square dimensions for the sides; ie, 30x30, or 48x48, since the load should scale in a more predictable way.
 
From what I've learned, the major difference in choosing to use acrylic or Lexan is the increased impact resistance that Lexan offers (used in bulletproof windows, among other things). For our purposes, the proper thickness acrylic will be more than sufficient when it comes to stability and, from what I'm told, is easier to work with (cleaner seams and nicer looking polished edges).

As far as a load calculator goes, here's one that I found that's been tested by custom aquarium builders (applies to rectangle tanks 8 feet or less in length):
acrylicthickness.jpg
 
So based on this, would 1" thick be appropriate for 36" of depth? I would think the pressure of the water would increase more exponentially than linearly.

Thanks for your reply!
 
actionplant;1939543; said:
So based on this, would 1" thick be appropriate for 36" of depth? I would think the pressure of the water would increase more exponentially than linearly.

Thanks for your reply!
Click to expand...

it is a function of depth alone, only one variable; therefore linear
 
actionplant;1939883; said:
Fantastic! Thanks. :)

Assuming that's conservative, would anyone here feel safe at 1.5" thick plexi on a 96" wide by 48" tall panel?
Click to expand...

96 x 48 tall with a closed top requires 1.899" I'd go with 2.00 if I were you..

Here's the kicker, I just call tenecor for a quote, with 96 length and 36" tall, I was quoted with 1" acrylic, while the calculator calls for 1.354" thickness..

Am I missing something here ?

stan
 
First of all, the panel thickness is "mostly" a function of depth. There is a point between 6' to about 15' long where a little thicker panel will be needed for depths of 4 feet or less. Then thickness becomes a function of depth. It is somewhat explained in the bottom link for constant forces, but with depth pressure, the pressure wouldn't be constant. Most of the charts just round up for safety.


http://www.soft4structures.com/PlateBuckling/bcpl_general_info.html
Also, this is complicated stuff without an engineering degree.

CRYO has a ridiculous safety factor of 12. I know that acrylic needs a generous safety factor to prevent buckling and crazing but that is a bit larger than most tank fabricators use. Also, CRYO is weaker than Reynolds Rcast and some other brands.

Most fabricators will be 1/4" thinner than CRYOs calculations for deep tanks.

There is this calculation for glass. The explanation is the same for an acrylic plate. The only difference would be the alpha and beta constants.
http://www.fnzas.org.nz/articles/technical/glassthickness/
 
Taking a look at what the CYRO calculator is performing--
The calculations are correct; the tensile strength and flexural strength of CYRO are about the same as most quality acrylics. Some are a little better some a little worse but all are pretty close.

If you copy the spreadsheet and paste into another sheet you can then modify the locked cells. The only one you want to change that is not red is the maximum allowable stress. 1500psi, half their safety factor, is what most tank fabricators use. It still has a safety factor 6X from failure on tensile strength and 10X on flexural strength.

As far as most of the charts, they are valid up to 8' long and 4' deep. When going longer than 8' you are best to bump up the thickness .25". When going deeper than 4' use the calculator.
 
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