Acrylic Safety Factor

R

ReefKeeperNYC

New member
I am learning and researching about acrylic since i recently built my own tank.

I have finally stumbled upon a pretty decent calculator.

Rivermud as they call it.
https://docs.zoho.com/sheet/published.do?rid=y0e2966628a3377884c538436cb0952d87ae4

I punched in my numbers and default the safety factor is 3.8.

The dimensions I built my tank actually equate to a safety factor of about 4.9/5.0.

What is the "minimum" safety factor when building an acrylic tank?

I am a firm believer in "overkill" in these scenarios, so to me a safety factor of 10 would be "minimum" for me lol

However realistically, What is the desired minimum safety factor to avoid situations in the future when building with acrylic? given the tanks are welded together as perfectly as possible.


User Defined Settings
Length 32.00 in 812.80 mm
Width 18.00 in 457.20 mm
Height 12.00 in 304.80 mm
Desired Safety Factor 4.8 sf

Recommendations
Glass Side/Back/Front 0.20 in 5.12 mm
Glass S/B/F Deflection 0.01 in 0.19 mm
Glass Bottom Thickness 0.25 in 6.35 mm
Glass Bottom Deflection 0.01 in 0.15 mm

Acrylic Wall Supported 0.268 in 6.82 mm
Acrylic Wall Unsupported 0.403 in 10.23 mm

Volume and Weight
Gallons and Litres 29.92 gal 113.27 L
Approx. Water Weight 249.85 lb 113.57 kg

Reverse SF Calculator
Side Thickness 0.2500 in 6.35 mm
Modified Safety Factor 7.4 sf 7.39 sf

Bottom Thickness 0.25 in 6.35 mm
Modified Safety Factor 4.8 sf 4.81 sf

Glass Weight
Length 32 in 1219.2 mm
Width 2418 in 609.6 mm
Gauge 0.5 in 12 mm
Weight 3047.20 lb 19.44 kg
 
In general I think many have agreed on the following for aquariums (glass and acrylic)
3.8 is used for rimmed/braced tank
7.6 rimless tank

But the choice is really yours..
In general anything above 1 indicates its capable of surviving the loads placed on it..
Now that assumes your calculation/formula is correct and assumes that the materials have the same structural qualities used in the formula,etc..

https://en.wikipedia.org/wiki/Factor_of_safety
 
mcgyvr said:
In general I think many have agreed on the following for aquariums (glass and acrylic)
3.8 is used for rimmed/braced tank
7.6 rimless tank

But the choice is really yours..
In general anything above 1 indicates its capable of surviving the loads placed on it..
Now that assumes your calculation/formula is correct and assumes that the materials have the same structural qualities used in the formula,etc..

https://en.wikipedia.org/wiki/Factor_of_safety
Click to expand...

Yes, that seems to be the mystery bag area if one doesnt purchase the tried and true brands successfully used in the cast acrylic brand pool.
 
Personally, I don't go by any degree of safety factor, per se. I engineer the tanks to have limited deflection; generally speaking Length/500. My thought is that to build in this way - the safety factor is inherent.

I've never seen a "simple" thickness calculator that I like, and I've been doing this for 30 years. In the example above, what does "supported" mean? How wide is that perimeter flange? any room for cross-bracing? how many cross-braces per any given length? Deflection tolerance? these are the things which determine thickness requirements far more than a "safety factor" :)

BTW, if you build the above tank; rimless 32 x 18 x 12" with 1/2"/12mm acrylic - it'll bow more than you or I would want to see.. 12"/12mm being the next available thickness up for .403"

James
 
Acrylics said:
Personally, I don't go by any degree of safety factor, per se. I engineer the tanks to have limited deflection; generally speaking Length/500. My thought is that to build in this way - the safety factor is inherent.

I've never seen a "simple" thickness calculator that I like, and I've been doing this for 30 years. In the example above, what does "supported" mean? How wide is that perimeter flange? any room for cross-bracing? how many cross-braces per any given length? Deflection tolerance? these are the things which determine thickness requirements far more than a "safety factor" :)

BTW, if you build the above tank; rimless 32 x 18 x 12" with 1/2"/12mm acrylic - it'll bow more than you or I would want to see.. 12"/12mm being the next available thickness up for .403"

James
Click to expand...

That is a great point. That caught my eye too. "œSupported" can leave one to assume too much.

What if the top was braced with 4" 1/4" strips going long way the 32" span?
 
ReefKeeperNYC said:
Is that the ewuation?

Length/50

And do you just convert height inches to mm?

12"-12mm
18"-18mm

And then step up?
Click to expand...
This is pretty generic, but it's pretty much the foundation I work from.
12" high, use 1/4" minimum
18" high, use 3/8" minimum
24" high, use 1/2" minimum
30" high, use 3/4" minimum
36" high, use 1" minimum
..and so on..

* Note: these are imperial thicknesses, i.e. 1/2" = 0.500" versus the "metric equivalent" which is 12mm = 0.472" For practical purposes, they are pretty much interchangeable.

Cross-braces: 6" wide cross-brace every 24" of tank length.

- So a 48 x 24" will have 3" perimeter eurobrace and a 6" crossbrace.
- If the same tank were 72" long - just one more crossbrace.
- At 8' length, I recommend jumping up one material thickness to keep deflection down.

For less bracing - it just depends on "how much" less.. everything changes at that point.

Rimless/unsupprted tanks *generally* get the "supported" thickness X 2.5 rather than 1.5 as many formulas will state.

* I know most tank mfrs use thinner material for the mass-produced tanks, but look at how much deflection they have.. Again, if you build to a deflection tolerance, the safety factors are inherent. If you build a tank just strong enough to "hold water" - you could get a big bubble on the front of your tank ;)

*my* simple equation for deflection tolerance is Length/500, unit of measurement doesn't matter. So if the span is 96", the deflection tolerance is 96"/500 or ~3/16" on a 96" span. Or you can look at it in metric units; ~2440mm/500 = the same. FWIW, most public aquariums engineer the tanks to Length/400 as a deflection tolerance, and some as low as Length/200.

Several reasons to build to a deflection tolerance rather than any formula but aside from long term strength and aesthetics, the primary issue most reef folks have with acrylic is scratching. If you have a bowed tank and place a flat scraper up against it - what happens? If you keep the deflection down, you keep the scratching down = means happier tank owner.

What if the top was braced with 4" 1/4" strips going long way the 32" span?
Click to expand...
Not knowing what you're starting with - kinda hard to say. But even if you built the tank from 1/4" material, a 4" perimeter flange would be okay :)

HTH,
James
 
Acrylics said:
This is pretty generic, but it's pretty much the foundation I work from.
12" high, use 1/4" minimum
18" high, use 3/8" minimum
24" high, use 1/2" minimum
30" high, use 3/4" minimum
36" high, use 1" minimum
..and so on..

* Note: these are imperial thicknesses, i.e. 1/2" = 0.500" versus the "metric equivalent" which is 12mm = 0.472" For practical purposes, they are pretty much interchangeable.

Cross-braces: 6" wide cross-brace every 24" of tank length.

- So a 48 x 24" will have 3" perimeter eurobrace and a 6" crossbrace.
- If the same tank were 72" long - just one more crossbrace.
- At 8' length, I recommend jumping up one material thickness to keep deflection down.

For less bracing - it just depends on "how much" less.. everything changes at that point.

Rimless/unsupprted tanks *generally* get the "supported" thickness X 2.5 rather than 1.5 as many formulas will state.

* I know most tank mfrs use thinner material for the mass-produced tanks, but look at how much deflection they have.. Again, if you build to a deflection tolerance, the safety factors are inherent. If you build a tank just strong enough to "hold water" - you could get a big bubble on the front of your tank ;)

*my* simple equation for deflection tolerance is Length/500, unit of measurement doesn't matter. So if the span is 96", the deflection tolerance is 96"/500 or ~3/16" on a 96" span. Or you can look at it in metric units; ~2440mm/500 = the same. FWIW, most public aquariums engineer the tanks to Length/400 as a deflection tolerance, and some as low as Length/200.

Several reasons to build to a deflection tolerance rather than any formula but aside from long term strength and aesthetics, the primary issue most reef folks have with acrylic is scratching. If you have a bowed tank and place a flat scraper up against it - what happens? If you keep the deflection down, you keep the scratching down = means happier tank owner.

Not knowing what you're starting with - kinda hard to say. But even if you built the tank from 1/4" material, a 4" perimeter flange would be okay :)

HTH,
James
Click to expand...

Wow! Thank you for the in depth knowledge!

I am very grateful for this info.

The whole build was with 1/4" top bottom and all verical panelas as well as the top brace strips. One end of the tank is setup with an internal fikter design so one piece of acrylic front to back making a chamber where the return pump and heater and skimmer will go.
 
James, will adding thickness and eurobracing eliminate the need for center bracing in a 48" span with less than 20" height? Not just acceptable but appropriate from builder viewpoint
 
ReefKeeperNYC said:
The whole build was with 1/4" top bottom and all vertical panels as well as the top brace strips. One end of the tank is setup with an internal filter design so one piece of acrylic front to back making a chamber where the return pump and heater and skimmer will go.
Click to expand...
Cool..I see the ol' water test goin' on... always good to see stuff hold water ;-)

James
 
drtrash said:
James, will adding thickness and eurobracing eliminate the need for center bracing in a 48" span with less than 20" height? Not just acceptable but appropriate from builder viewpoint
Click to expand...
Of course :)
You can make a tank not require any bracing (rimless) if you make it thick enough :)

If this is a 55 though, it's a bit messy in that the front to back depth is only 12.5-13" so you're limited no matter what you do. This is where I'd usually opt for a crossbrace and an even narrower euro-brace. Like use 1/2" acrylic with 2" euro-brace and a single cross-brace. This would yield 2 openings that are more like 20 x 9" which to me, is much more serviceable than a single 6-7" wide opening, no matter how long

James
 
Acrylics said:
Cool..I see the ol' water test goin' on... always good to see stuff hold water ;-)

James
Click to expand...

Thanks for checking in!

I actually have the tank filled.

There is minimal to no bowing. Max 1/16" if at all from my measuring.

No panels have popped off (knock on wood) so far and I am not seeing any leaks thus far.

I was debating adding some braces front to back on top. Would thisxadd any support or make matters worse or futile?

Also does no bowing mean no problem?
 
ReefKeeperNYC said:
Thanks for checking in!

I actually have the tank filled.

There is minimal to no bowing. Max 1/16" if at all from my measuring.

No panels have popped off (knock on wood) so far and I am not seeing any leaks thus far.

I was debating adding some braces front to back on top. Would this add any support or make matters worse or futile?

Also does no bowing mean no problem?
Click to expand...
Place a straightedge across the front at the top - where the euro-brace is attached. If there is no significant bowing there, then adding a cross-brace might help you sleep at night - but won't do much to/for the tank.

Measure deflection in about a month. Acrylic is porous and 1/4" acrylic will reach it's saturation point in about 4-6 weeks, so at 4-6 weeks, barring any other issues - it'll bow about as much as it ever will. Given that it's minimal now is only good news. So pat yourself on the back and enjoy a cold one :)

James
 
Acrylics said:
Place a straightedge across the front at the top - where the euro-brace is attached. If there is no significant bowing there, then adding a cross-brace might help you sleep at night - but won't do much to/for the tank.

Measure deflection in about a month. Acrylic is porous and 1/4" acrylic will reach it's saturation point in about 4-6 weeks, so at 4-6 weeks, barring any other issues - it'll bow about as much as it ever will. Given that it's minimal now is only good news. So pat yourself on the back and enjoy a cold one :)

James
Click to expand...

Woop woop!

Thanks!

I think itll be a well deserved cold one!
 
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