Glass strength and double laminate

dallasg

dallasg

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Hi,

just a quick Q about glass, 24mm laminate glass is made from 2 12mm sheets bonded together, this is done to make the glass stronger for bullet proofing etc, but is the strength of the pane still not the same as a single 12mm sheet in the sense that what if one of the panes in the laminate crack, surely then the pressure will be to great for the uncracked 12mm piece?

i might be totally off here, but just something i am curious about, or does the laminate "weld" the glass into "1" piece?

thanks
 
hey dallas
we built a small tank using 6mm laminate glass, meaning 3mm, laminate and another 3mm glass. Filled up, everything went well for 30 min then the inside glass cracked followed by the outside one. did some research and replaced with single sheet of 6mm glass and it`s been going for a long time now.
hope that might help.
 
dallasg said:
Hi,

just a quick Q about glass, 24mm laminate glass is made from 2 12mm sheets bonded together, this is done to make the glass stronger for bullet proofing etc, but is the strength of the pane still not the same as a single 12mm sheet in the sense that what if one of the panes in the laminate crack, surely then the pressure will be to great for the uncracked 12mm piece?

i might be totally off here, but just something i am curious about, or does the laminate "weld" the glass into "1" piece?

thanks
Click to expand...

Dallas

You are wrong:). While the glass is not exactly welded into one piece, the two combined with the laminate is massively stronger than one on its own.

Glyn has just built a tank from 3 x 12mm glass that is 1.2m high or so. If the laminate was no stronger than one 12mm on its own it would have burst long before it was even completely full.

True laminate glass is not quite as strong as the equivalent in monolithic glass, as there is slightly more flex due to the laminate sheet, but it is almost.:thumbup:

Cheers

Rob.
 
I agree with Rob. I was involved with a 33000l octagonal tank that had 8 1500 x 1500 x 51mm laminate panels. One of the panels cracked a few pains due to the frame not been installed correctly. If this panel had have been float glass R50k salt water would have spilt onto the wooden deck and evergreen grass.


Laminate glass has it's benefits. I personally do not like it because it discolours in time and sometimes the laminate parts, causing marks in the pains. IMO
 
nice thread Dallas, and awesome answers guys !!
 
Leslie Hempel has answered this question before, saying that its only as strong as one pane.
Will 10mm safety glass work? - General Discussions
Post 7

"dude my opinion is this, as i have said many mines before Laminated lass is actually weaker than normal float (normal) glass as it will only be as strong as the strength of the thiskest piece(10mm laminate - 2 x 5mm pieces laminated together - total strength is equal to 1 x 5mm piece) not to mention more expensive. 10mm normal glass will be fine for a tank 2.000L x .600W x .450H the biggest i would go in 10mm would be 2.5 x .700 x .700 but have seen bigger and am wary. other factors to consider are the positioning of holes and the overall design.

i hope that helps"
 
Agree with Rob.. Must also add that it is not recomened by the supplier to drill holes in the laminated panels just thought I would share that bit f info too
 
@Donn "CARP" The 33000 litre tank is 2.5 meters deep the panels are made of 5x10mm pains. I will be interested to hear how this tank of 4 years has managed to stay intact should your opinion be correct.
 
@ Nemos Janitor, that was a quote from another thread by Leslie Hempel.
I stated on that thread that im of the opinion that it would be stronger and the members disagreed.
 
Interesting thread...
Ross tank is 2 x 8mm glass laminated and Adriaan done it this way because Ross wanted the tank rimless..
Maybe Adriaan should give us an answer here as i saw two tanks built by him where he used laminated glass and both tanks are rimless, so surely, laminated glass is stronger if it holds rimless tanks together?????
 
Ridwaan cant agree more. Put it this way if you had to put two pieces of metal together do you think it is going to take the same amount of strength to bend it? NO it wont so I cant see why some guys think that 2 10mm pieces of glass will not be stonger than 1 piece of 10mm. Almost the same as useing Euro bracing if it did not help strenthen the tank why would we be adding it
 
From Pilkington Glass

The ASTM E 1300 Standard Practice for Determining Load Resistance of Glass in Buildings should be consulted for glass capacity under specified loads. The strength of glass can be doubled by heat-strengthening, or quadrupled by full-tempering. Note that annealed glass suffers a static fatigue effect which makes it only half as strong under long term loads (aquarium loads, snow loads, etc.) as under short term loads, such as wind gusts.
Laminated glass is 50% to 100% as strong (depending on aspect ratio and framing details) as monolithic glass of the same overall thickness and size when subjected to short duration loads at room temperatures.
Symmetrical insulating glass, where both lights are the same thickness, can carry almost twice the uniform load, as one of the lights on its own.
Glass has a finite probability of breakage under load. Its strength cannot be exactly predicted. For this reason, good design practice, while attempting to prevent glass breakage, will also always consider the possibility and consequences of unanticipated breakage.

Annealed and heat-strengthened glass will break into large pieces when the applied load exceeds the glass strength. Most of the pieces remain in a glazed opening unless further force is applied. Laminated glass requires a considerable load to force it from a glazed opening even when both lites are broken. It can, however, be pierced by dense, hard, falling objects. Tempered glass breaks into very small pieces which can easily fall from a glazed opening, and often fall in small clumps which do not separate until they hit the ground...
... On large sizes, the glass thickness needed may be decided by deflection limits rather than glass strength. Note that equal thicknesses of annealed, heat-strengthened and tempered all deflect the same amount under equal loads. Laminated glass, at room temperature, of the same thickness, will deflect about the same amount for short duration loads (seconds) but will behave as sliding layers and deflect further under long duration loads (hours or days).
Click to expand...
Hennie
 
hennie i think you have pointed out what i have struggled to find the correct wording to express.. laminate is a safety glass that deflects and then retains its usual composition. EG; i have run into a sliding door consisting of 6.38mm laminate glass at full pace (not intensionally of course) and have been flung back over 2 meters (i weighed around 65kg at the time) if you place a consistent pressure on the same thickness glass it will finally succumb to the pressures exherted on it. for smaller tanks where an oversized thickness laminate glass is used EG: 2m x .600 x .600 tank in 20mm laminate yould most definatley work as the minimum thickness of normal float (flat glass) required is between 10 and 12mm depending on structural loads (due to placement of holes etc) exherted on it... in bigger tanks i would assume that so long as the proportions are kept in check (laminate glass thickness doubled in comparison to flat glass) it would probably work but there would be other factors that come into play EG: parting of the laminate over time due to moisture seeping between the panes, the unproven cracking of one pane due to varying temperature differences in the 2 pieces of the laminate glass glass.

in closing, laminate glass is not designed to be used for the purpose in which we want to use it for (aquaruims). It is meant to limit harm in a situation where normal glass will most certainly inflict harm such as car windows and sliding doors EG: it is law that laminates or toughened be put in any area below .600mm off the ground or in doors containg glass, as a glazer you are not allowed to place normal glass in such areas.

tempered glass would be a better option but would also be subject to the correct sizing in comparision to load. just because it is stronger does not mean it will not eventually succumb to an consistent overload if incorrectly calculated.

i dont proclaim to know all there is about glass and its strengths, but this is what i have learnt in my time of working with it. i am however always very cautious and personally prefer to overspec on glass thickness if there will be doubt.
 
I ran through a tempered glass door (not intentionally) and there was millions of glass pieces everywhere. Up to 6 meters away!

I will never build a tank with that. One hit and full glass pane gives way resulting in all water livestock sand rocks whatever else in the tank to be on the floor within one second. You will not even have time to react, or say your favourite swear word.

Where normal glass will crack, leaving you with a nice waterfall squirting out the side, giving you time to react, swear, run around totally confused to get some buckets....

Seems laminate will work, as long as you double up on thickness. Nice for rimless tanks, but no use on tanks with euro bracing.

My 2c
 
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