Glass thickness and how water pressure works?

PokerG · 01/17/2006, 03:19 AM

Everyone knows that the thickness of the glass goes up when the tank gets higher not because of the water volume per se, but because of the way the water wants to squeeze out the sides.

Is there a proper calculation for working out the thickness used for unusual setups?

For instance:

1: Someone wants to build a tank thats 4ft high but only 12"x12" for the other dimensions. The normal recomendation for tanks of this height is close to 1" thick glass. But for a tank that is only 12"x12" this would be overkill. So how do you do the maths to get the correct thickness?

2: (And my actual situation) I want to build a tank that is 12-14ft long 12-15" high and 12" deep. Now the glass is more likely to bow in the middle than your standard 40G (48"Lx12"Dx15"H). Should I use thicker glass?

What are the precise benefits to bracing that goes along the glass and that goes front to back? (I realise that going along the glass makes the glass less likely to bend as now the brace had to bend as well effectively increasing it strength, same goes for the front to back bracing, but how much is the benefit. I basically need some maths if people have any to show how to calculate tank strengths when filled with water etc.

Bit of a waffle I know but thanks for your help if you can.

Gary

Fl_seagull · 01/17/2006, 09:02 AM

Glass Thickness is an often discussed topic. The fnzas site explains it better than I can.

I know I have posted a spreadsheet that I have used before. But, currently I can not find my copy. The Fnzas site no longer has a link to the calculator

Fl_seagull · 01/17/2006, 09:24 AM

Quote:

Originally posted by PokerG
What are the precise benefits to bracing that goes along the glass and that goes front to back? (I realise that going along the glass makes the glass less likely to bend as now the brace had to bend as well effectively increasing it strength, same goes for the front to back bracing, but how much is the benefit.

In your case the use of a 2" to 3" bracing around the tank may not be the best option because of the narrow tank width. After all a 3" brace front and back leaves less than 6" to access the tank. You may find it better to put in a 6" wide brace every 18" to 24".

If you are using acrylic the brace around the edge is more important since acrylic allows more bowing. This is more a viewing issue than strength issue IMO.

windsor-aquatic · 01/17/2006, 11:58 AM

I would first check that glass is available in the lengths you mention. You don't indicate where you are, but I spoke to a manufacturer in Canada recently regarding a large tank , and was surprised to find that the longest length of starphire he could obtain was 126 inches. In the UK the same glass is available up to 6.5 metres (256 inches). The previous comments about bracing are very valid, especially the front to back suggestion.

norskfisk · 01/17/2006, 12:28 PM

Actually the glassthickness calculator is still on the fnzas site here:

http://www.fnzas.org.nz/articles/tec...lass_complete/

To answer part of your question:
On the sides 6mm glass is plenty thick enough for the 14' by 15'' tank. Safety factor 3.3.
But this assumes bracing along the top.
Without bracing and thickness for bottom panel I cannot answer.

windsor-aquatic · 01/17/2006, 12:34 PM

On a personal note, I wouldn't want to make a tank of that length without the addition of bracing bars. All glass will tend to bend slightly under water pressure, and that's a long length of glass and therefore a lot of potential bending!

PokerG · 01/18/2006, 06:08 AM

I have a 9ft reef upstairs that has both lengthwise and front to back bracing at various points along the tank. I just didn't like the idea of using 2" lengthwise bracing front and back as this really would make access to the tank difficult as Fl_seagull pointed out.

The site you guys pointed me to is great, thanks I really appreciate it.

Gary

ERICinFL · 01/18/2006, 09:50 AM

Try this to help you. http://www.garf.org/
Go to the DIY section and select tank building. Enter your dimensions and it'll give you it's recommendation.

PokerG · 01/18/2006, 04:34 PM

Garf doesnt recomend you build tanks this size, thats one of the reasons I started to ask around.

But thanks for the response.

Gary

Fl_seagull · 01/18/2006, 06:49 PM

Handling large or long piece of glass can be very scary. Having had a sheet of glass 8 ft long and 3 ft high break in your hands and drop razor sharp pieces around your feet is not something I want to experience again.

Your front, back and bottom pieces are large enough that you may find just handling them will cause them to break.

Also, remember to have the glass shop "seam" the glass square. Some (most where I live) of the shops will not sell unseamed glass. Cutting glass leaves a razor sharp edge. "Seaming" grind the edge so it is safe to handle. In aquarium building these seamed edges makes for better (stronger) joints.

PokerG · 01/19/2006, 04:13 AM

Fl_seagull, I am guessing the place I am will get the glass will sell it already seamed but it will be worth asking. thanks.

Gary

Fl_seagull · 01/19/2006, 06:03 AM

The shops here quote it as $0.22 to $0,25 an inch! It may have been included in the cost you were quoted. The last quote I got had seaming as 1/2 the cost of the bill.

01/17/2006, 03:19 AM	#1
PokerG Registered Member Join Date: Jun 2005 Location: High Wycombe, England, UK Posts: 63	Glass thickness and how water pressure works? Everyone knows that the thickness of the glass goes up when the tank gets higher not because of the water volume per se, but because of the way the water wants to squeeze out the sides. Is there a proper calculation for working out the thickness used for unusual setups? For instance: 1: Someone wants to build a tank thats 4ft high but only 12"x12" for the other dimensions. The normal recomendation for tanks of this height is close to 1" thick glass. But for a tank that is only 12"x12" this would be overkill. So how do you do the maths to get the correct thickness? 2: (And my actual situation) I want to build a tank that is 12-14ft long 12-15" high and 12" deep. Now the glass is more likely to bow in the middle than your standard 40G (48"Lx12"Dx15"H). Should I use thicker glass? What are the precise benefits to bracing that goes along the glass and that goes front to back? (I realise that going along the glass makes the glass less likely to bend as now the brace had to bend as well effectively increasing it strength, same goes for the front to back bracing, but how much is the benefit. I basically need some maths if people have any to show how to calculate tank strengths when filled with water etc. Bit of a waffle I know but thanks for your help if you can. Gary

01/17/2006, 09:02 AM	#2
Fl_seagull Registered Member Join Date: May 2004 Posts: 206	Glass Thickness is an often discussed topic. The fnzas site explains it better than I can. I know I have posted a spreadsheet that I have used before. But, currently I can not find my copy. The Fnzas site no longer has a link to the calculator __________________ I try to learn from other's mistakes but my own are more entertaining. Current Tank Info: 125 gal Reef, 120 FO, 6 gal soft coral/LPS Nano

01/17/2006, 12:28 PM	#5
norskfisk Registered Member Join Date: Aug 2003 Location: Norway Posts: 206	Actually the glassthickness calculator is still on the fnzas site here: http://www.fnzas.org.nz/articles/tec...lass_complete/ To answer part of your question: On the sides 6mm glass is plenty thick enough for the 14' by 15'' tank. Safety factor 3.3. But this assumes bracing along the top. Without bracing and thickness for bottom panel I cannot answer. __________________ Jon Olav

01/18/2006, 09:50 AM	#8
ERICinFL Rejisturd Mimbur Join Date: Oct 2005 Location: Brevard County, FL Posts: 1,346	Try this to help you. http://www.garf.org/ Go to the DIY section and select tank building. Enter your dimensions and it'll give you it's recommendation. __________________ Ummmm... yeah... don't touch the Mag Float. Sorry kids, your college fund is gone, but the tank looks SWEET right? Current Tank Info: 150gal mixed reef. ER CS135, 65gal sump/fuge with a Mag12 return. (2) Korillia 4s, (1) modded MJ1200, two SunSun 3200gph powerheads. 250+lbs LR.

01/18/2006, 06:49 PM	#10
Fl_seagull Registered Member Join Date: May 2004 Posts: 206	Handling large or long piece of glass can be very scary. Having had a sheet of glass 8 ft long and 3 ft high break in your hands and drop razor sharp pieces around your feet is not something I want to experience again. Your front, back and bottom pieces are large enough that you may find just handling them will cause them to break. Also, remember to have the glass shop "seam" the glass square. Some (most where I live) of the shops will not sell unseamed glass. Cutting glass leaves a razor sharp edge. "Seaming" grind the edge so it is safe to handle. In aquarium building these seamed edges makes for better (stronger) joints. __________________ I try to learn from other's mistakes but my own are more entertaining. Current Tank Info: 125 gal Reef, 120 FO, 6 gal soft coral/LPS Nano

01/17/2006, 11:58 AM	#4
windsor-aquatic Registered Member Join Date: Jul 2005 Location: sheffield, uk Posts: 184	I would first check that glass is available in the lengths you mention. You don't indicate where you are, but I spoke to a manufacturer in Canada recently regarding a large tank , and was surprised to find that the longest length of starphire he could obtain was 126 inches. In the UK the same glass is available up to 6.5 metres (256 inches). The previous comments about bracing are very valid, especially the front to back suggestion.

01/17/2006, 12:34 PM	#6
windsor-aquatic Registered Member Join Date: Jul 2005 Location: sheffield, uk Posts: 184	On a personal note, I wouldn't want to make a tank of that length without the addition of bracing bars. All glass will tend to bend slightly under water pressure, and that's a long length of glass and therefore a lot of potential bending!

01/18/2006, 06:08 AM	#7
PokerG Registered Member Join Date: Jun 2005 Location: High Wycombe, England, UK Posts: 63	I have a 9ft reef upstairs that has both lengthwise and front to back bracing at various points along the tank. I just didn't like the idea of using 2" lengthwise bracing front and back as this really would make access to the tank difficult as Fl_seagull pointed out. The site you guys pointed me to is great, thanks I really appreciate it. Gary

01/18/2006, 04:34 PM	#9
PokerG Registered Member Join Date: Jun 2005 Location: High Wycombe, England, UK Posts: 63	Garf doesnt recomend you build tanks this size, thats one of the reasons I started to ask around. But thanks for the response. Gary

01/19/2006, 04:13 AM	#11
PokerG Registered Member Join Date: Jun 2005 Location: High Wycombe, England, UK Posts: 63	Fl_seagull, I am guessing the place I am will get the glass will sell it already seamed but it will be worth asking. thanks. Gary

01/19/2006, 06:03 AM	#12
Fl_seagull Registered Member Join Date: May 2004 Posts: 206	The shops here quote it as $0.22 to $0,25 an inch! It may have been included in the cost you were quoted. The last quote I got had seaming as 1/2 the cost of the bill. __________________ I try to learn from other's mistakes but my own are more entertaining. Current Tank Info: 125 gal Reef, 120 FO, 6 gal soft coral/LPS Nano