mrcrab
In Memoriam
I've posted some questions here and would greatly appreciate any advice, feedback.
http://reefcentral.com/forums/showt...threadid=773774
Thanks
http://reefcentral.com/forums/showt...threadid=773774
Thanks
Physicists and wood tank builders...
- Thread starter mrcrab
- Start date
mrcrab
In Memoriam
Thnaks for the heads up. That was weird...just cut and pasted the link from the original post.
Let's see if this works:
http://reefcentral.com/forums/showthread.php?s=&threadid=773774
Let's see if this works:
http://reefcentral.com/forums/showthread.php?s=&threadid=773774
mrcrab
In Memoriam
Ill bump this and add some info for others.
These are some links I've found so far. If you find any other useful one's please attach them for the ride.
http://www.reefcentral.com/forums/s...threadid=686757
http://reefcentral.com/forums/showt...threadid=716410
http://www.reefcentral.com/forums/s...25&pagenumber=1
http://garf.org/tank/buildtank.asp
These are some links I've found so far. If you find any other useful one's please attach them for the ride.
http://www.reefcentral.com/forums/s...threadid=686757
http://reefcentral.com/forums/showt...threadid=716410
http://www.reefcentral.com/forums/s...25&pagenumber=1
http://garf.org/tank/buildtank.asp
Fred_J
New member
People who try to go through and help others by responding to unanswered questions (posts with no replies) will see the title of your post with 6 replies and not bother viewing it because it appears to be answered. This is why bumping a thread does more harm than good.
I would help but it is over my head.
Fred
I would help but it is over my head.
Fred
Thnaks for the heads up. That was weird...just cut and pasted the link from the original post.
If you cut and paste a link that has an abbreviation in it (the ....) then it will be a faulty link when pasted because it is missing the info in the middle.
If you cut and paste a link that has an abbreviation in it (the ....) then it will be a faulty link when pasted because it is missing the info in the middle.
sphelps
Premium Member
If the starphire is only available to lengths up to 8 feet then I say make it 8 feet. If this is a true in wall tank then I believe you can only have 2 viewing sides if it's placed in a corner. One inch plywood is good and 1/2" (12mm) glass for the sides and euro bracing will be good as well.
Here's what I was thinking:
First the plywood part:
Then the side glass panels cut to fit perfectly inside the plywood:
Then the euro bracing with 2 cross braces, which will overlap both the glass and the plywood (I think 4" width for all bracing will work well):
let me know if this is what you had in mind. You could use 3 400W metal halides quite nicely with the cross bracing.
Here's what I was thinking:
First the plywood part:
Then the side glass panels cut to fit perfectly inside the plywood:
Then the euro bracing with 2 cross braces, which will overlap both the glass and the plywood (I think 4" width for all bracing will work well):
let me know if this is what you had in mind. You could use 3 400W metal halides quite nicely with the cross bracing.
mrcrab
In Memoriam
Wow! Thanks.
That's exactly what we were thinking. We'll by an 8' X 4' panel of 1/2" starfire and have it cut in half lengthwise and laminated for a 1" think front viewing panel. It will only be viewable on the front panel. The side panels will actually be in the garage viewable by me.
We'll be using 1" marine ply all around sealed with epoxy resin reinforced with fiberglass cloth and will be bracing it with SS threaded rods sealed in cpvc.
The side panels will be just regular 5/8" tempered glass.
I think the 1" laminated starfire will give us an extra measure of security. The overflow will be an exterior box along the entire back, 4" wide interior measurement with 4 x 2" overflows for the sump, frag tank and cl.
Once the final plans are drawn we'll post here for final approval from the experts.
Thanks again
Once we get everything figured out, we'll document with lots of pics
That's exactly what we were thinking. We'll by an 8' X 4' panel of 1/2" starfire and have it cut in half lengthwise and laminated for a 1" think front viewing panel. It will only be viewable on the front panel. The side panels will actually be in the garage viewable by me.
We'll be using 1" marine ply all around sealed with epoxy resin reinforced with fiberglass cloth and will be bracing it with SS threaded rods sealed in cpvc.
The side panels will be just regular 5/8" tempered glass.
I think the 1" laminated starfire will give us an extra measure of security. The overflow will be an exterior box along the entire back, 4" wide interior measurement with 4 x 2" overflows for the sump, frag tank and cl.
Once the final plans are drawn we'll post here for final approval from the experts.
Thanks again
Once we get everything figured out, we'll document with lots of pics
sphelps
Premium Member
I don't think you need a full inch of glass for the viewable side, it will decrease the clarity HUGE. 1/2" will be fine if a Euro Bracing and cross bracing is used similar to the drawing. You may have read somewhere that 1/2" will have a low safety factor with that lenght and hieght, however you're only using 1/2" on one side and the increase of tank hieght increases the load on the bottom of the tank, but you have 1" ply on the bottom, so you're good. Also you're side seams will be stronger than regular glass tanks using only silicone. Bottom line is 1" glass for that section is huge overkill, and decrease you visibilty by 50%, I beleive starphires only about twice as clear as regular glass so 1" starphire would be like 1/2" regular.
mrcrab
In Memoriam
Don't take this wrong, because I really appreciate your input and I would much rather just use 1/2" glass, but just to make sure...you know what they say about advice, it's worth what you pay for it, and I don't want a huge 300 + gallon disaster on my hands.
How many tanks of this size have you built or what type of background do you have that would lead you to make the decision that 1/2" is adequate?
I'd much rather be safe than sorry.
What would be the maximum height for the front panel and would you recommend tempering the front panel for additional strength?
Thanks
How many tanks of this size have you built or what type of background do you have that would lead you to make the decision that 1/2" is adequate?
I'd much rather be safe than sorry.
What would be the maximum height for the front panel and would you recommend tempering the front panel for additional strength?
Thanks
sphelps
Premium Member
Fair enough, letââ"šÂ¬Ã¢"žÂ¢s clear up these issues. First off Iââ"šÂ¬Ã¢"žÂ¢m a currently a 3rd year Mechanical Engineering student at the University of Saskatchewan. Iââ"šÂ¬Ã¢"žÂ¢ve taken 2 courses on fluid mechanics alone, and currently completing my third. The largest tank Iââ"šÂ¬Ã¢"žÂ¢ve build is only 135gal, and it happens to be my tank, however I do see how this really that relevant. I didnââ"šÂ¬Ã¢"žÂ¢t do any calculations to calculate the glass size I recommended I was simply going on what Iââ"šÂ¬Ã¢"žÂ¢ve seen. Hereââ"šÂ¬Ã¢"žÂ¢s a link to someone who built a plywood tank (bigger than yours) and used 12mm glass for viewing panels: http://home.online.no/~joobjoer/eng_diy/2200litre/2200litres.html
But since you asked lets do some elementary calculations to back up my claim.
In order to figure out if the glass will be strong enough we should examine the weakest point or where the greatest hydrostatic force acts. This point will be located somewhere on the front view panel. We can find this resultant hydrostatic force quite easily:
F = ã Hcg A
Where:
ã = specific weight of seawater = density x gravitational force = 1025kg/mÃ"šÃ‚³ x 9.81m/sÃ"šÃ‚² = 10055.25
Hcg = the height from the centroid to the top of the water level. In our case we can make this value equal to half the height of the glass and assume the tank will completely full.
A = the area of the plane in question = 0.762m x 2.4384m = 1.858mÃ"šÃ‚²
So F = (10055.25)(0.381m)(1.858mÃ"šÃ‚²) = 7118.09N
To balance the bending moment potion of stress the resultant force from the fluid does not act through the centroid of the glass but below it towards the higher pressure. This line of action passes through the center of pressure (CP) of the plane.
To find the coordinates (Xcp, Ycp) of the point in which the resultant hydrostatic force acts we sum the moments of the element force pdA about the centroid and equate to the moment of the resultant F. However since the other side of the glass is at atmospheric pressure the ambient pressure can be neglected because it acts on both sides. Therefore the center of pressure is independent of specific weight and this simplifies our calculations.
Xcp = 0 in our case as the glass face is perfectly rectangular, therefore the position will be directly below the centroid (not to the left or right of it).
Ycp = (Ixx sinè)/(Hcg A)
Ixx = moment of inertia with respect to the x-axis (horizontal) =
(length x heightÃ"šÃ‚³)/ 12 = (2.4384m)(0.762m)Ã"šÃ‚³/12 = 0.0899m^4
è = 90Ã"šÃ‚° since the glass plane in question is vertical.
Therefore Ycp = ((0.0899)(sin90))/((0.381)(1.858)) = 0.127m
This means the point CP is located 0.127m below the centroid.
So now we just need the reaction forces located at the bottom and top of the glass where the plywood holds the glass.
R-bottom = 4815.4N
R-top = 2372.7N
These where calculated by summing the moments about the bottom point and then the top point.
Now the maximum bending moment occurs at CP and is equal to (4815.4N)(0.254m) = 1223.1Nm.
Next we calculate the elastic section modulus (this is where glass thickness comes in):
For rectangular shapes: S = (1/6)htÃ"šÃ‚²
t = glass thickness = 12mm = 0.012m
h = tank height = 0.762m
S = (1/6)(0.762)(0.012m)Ã"šÃ‚² = 1.8288 x10^-5mÃ"šÃ‚³
Now we can finally calculate the maximum stress that will occur in the glass:
This equal to the maximum moment over the elastic section modulus:
(1223.1Nm)/(1.8288x10^-5) = 66.88 MPa
If you use 24mm glass the maximum stress would be = 16.72 MPa
So there you have it. Iââ"šÂ¬Ã¢"žÂ¢m not sure what the tensile strength of glass is but you want it to be more that the max stress calculated above. I believe itââ"šÂ¬Ã¢"žÂ¢s somewhere in between 69 and 120 MPa depending upon the type. Tempered glass would be even higher probably anywhere from 120 to 370 MPa. Not sure though on these numbers.
Side Notes:
The above calculations are only valid if both the bottom and the top of the tank have adequate bracing.
The above calculations should only be used for plywood tanks, as all glass tanks are joined with silicone which means the weakest point would be at the seams.
A safety factor was not used, however the actual water height will be lower than what was used in calculations.
Only the weakest point was examined.
There is a possibility I could have miss calculated, thereââ"šÂ¬Ã¢"žÂ¢s no guarantee the glass will experience the above stresses (could be more could be less).
All units were converted to SI units.
Work Cited:
Engineering Material Science, William D. Callister
Fluid Mechanics 5th Edition, Frank M. White
But since you asked lets do some elementary calculations to back up my claim.
In order to figure out if the glass will be strong enough we should examine the weakest point or where the greatest hydrostatic force acts. This point will be located somewhere on the front view panel. We can find this resultant hydrostatic force quite easily:
F = ã Hcg A
Where:
ã = specific weight of seawater = density x gravitational force = 1025kg/mÃ"šÃ‚³ x 9.81m/sÃ"šÃ‚² = 10055.25
Hcg = the height from the centroid to the top of the water level. In our case we can make this value equal to half the height of the glass and assume the tank will completely full.
A = the area of the plane in question = 0.762m x 2.4384m = 1.858mÃ"šÃ‚²
So F = (10055.25)(0.381m)(1.858mÃ"šÃ‚²) = 7118.09N
To balance the bending moment potion of stress the resultant force from the fluid does not act through the centroid of the glass but below it towards the higher pressure. This line of action passes through the center of pressure (CP) of the plane.
To find the coordinates (Xcp, Ycp) of the point in which the resultant hydrostatic force acts we sum the moments of the element force pdA about the centroid and equate to the moment of the resultant F. However since the other side of the glass is at atmospheric pressure the ambient pressure can be neglected because it acts on both sides. Therefore the center of pressure is independent of specific weight and this simplifies our calculations.
Xcp = 0 in our case as the glass face is perfectly rectangular, therefore the position will be directly below the centroid (not to the left or right of it).
Ycp = (Ixx sinè)/(Hcg A)
Ixx = moment of inertia with respect to the x-axis (horizontal) =
(length x heightÃ"šÃ‚³)/ 12 = (2.4384m)(0.762m)Ã"šÃ‚³/12 = 0.0899m^4
è = 90Ã"šÃ‚° since the glass plane in question is vertical.
Therefore Ycp = ((0.0899)(sin90))/((0.381)(1.858)) = 0.127m
This means the point CP is located 0.127m below the centroid.
So now we just need the reaction forces located at the bottom and top of the glass where the plywood holds the glass.
R-bottom = 4815.4N
R-top = 2372.7N
These where calculated by summing the moments about the bottom point and then the top point.
Now the maximum bending moment occurs at CP and is equal to (4815.4N)(0.254m) = 1223.1Nm.
Next we calculate the elastic section modulus (this is where glass thickness comes in):
For rectangular shapes: S = (1/6)htÃ"šÃ‚²
t = glass thickness = 12mm = 0.012m
h = tank height = 0.762m
S = (1/6)(0.762)(0.012m)Ã"šÃ‚² = 1.8288 x10^-5mÃ"šÃ‚³
Now we can finally calculate the maximum stress that will occur in the glass:
This equal to the maximum moment over the elastic section modulus:
(1223.1Nm)/(1.8288x10^-5) = 66.88 MPa
If you use 24mm glass the maximum stress would be = 16.72 MPa
So there you have it. Iââ"šÂ¬Ã¢"žÂ¢m not sure what the tensile strength of glass is but you want it to be more that the max stress calculated above. I believe itââ"šÂ¬Ã¢"žÂ¢s somewhere in between 69 and 120 MPa depending upon the type. Tempered glass would be even higher probably anywhere from 120 to 370 MPa. Not sure though on these numbers.
Side Notes:
The above calculations are only valid if both the bottom and the top of the tank have adequate bracing.
The above calculations should only be used for plywood tanks, as all glass tanks are joined with silicone which means the weakest point would be at the seams.
A safety factor was not used, however the actual water height will be lower than what was used in calculations.
Only the weakest point was examined.
There is a possibility I could have miss calculated, thereââ"šÂ¬Ã¢"žÂ¢s no guarantee the glass will experience the above stresses (could be more could be less).
All units were converted to SI units.
Work Cited:
Engineering Material Science, William D. Callister
Fluid Mechanics 5th Edition, Frank M. White
DesertBandits
New member
I think you should go to Garf's site. They have plans and a calculator to tell you how thick to go on everything. By the way laminated glass is only like 75% as strong as the real thing.
Sphelps,
If you have Callister, you should know that the highest stresses in ceramics occur at defects that serve as stress-raising regions, like inclusions and cracks. That's why 4, not 3-point bending tests are used on ceramics - fracture is somewhat statistical in these types of materials, and you must consider a region with an even stress, which isn't the case with a 3-point test, or a tank panel for that matter. Tabulated tensile strengths for ceramics are less useful than for many other materials, as they are so seldomly used for situations under tensile loads.
In this situation, you's have to consider the actual deflection of the piece. Young's modulus is a fourth order tensor, making the calculation complicated for a thick panel braced on all edges.
Tempered glass does not have a higher tensile strength than untempered. The piece is air quenched so the outer surface has a residual compressive stress. This stress has to be overcome in a bending situation before the tensile regime is reached, so the piece can support higher loads.
Good luck in school - don't work too hard.
G1
If you have Callister, you should know that the highest stresses in ceramics occur at defects that serve as stress-raising regions, like inclusions and cracks. That's why 4, not 3-point bending tests are used on ceramics - fracture is somewhat statistical in these types of materials, and you must consider a region with an even stress, which isn't the case with a 3-point test, or a tank panel for that matter. Tabulated tensile strengths for ceramics are less useful than for many other materials, as they are so seldomly used for situations under tensile loads.
In this situation, you's have to consider the actual deflection of the piece. Young's modulus is a fourth order tensor, making the calculation complicated for a thick panel braced on all edges.
Tempered glass does not have a higher tensile strength than untempered. The piece is air quenched so the outer surface has a residual compressive stress. This stress has to be overcome in a bending situation before the tensile regime is reached, so the piece can support higher loads.
Good luck in school - don't work too hard.
G1
salty joe
Active member
Hey G1, I'm a little cofused. I wonder if you could enlighten me.
Does tempered glass have a similar property to stressed steel encased in concrete used for bridges?
If tempered glass does not have a greater tensile strength than non-tempered glass, yet it can carry a greater load, how is it stronger?
Can you say how much stronger tempered is than non-tempered in percentage, or does that depend on size & thickness?
I heard that tempered glass is harder than non-tempered. If true, do you know how much harder?
And finally, is there a standard for tempering glass to ensure uniformity?
Thanks,
Joe
