Interesting that the glass itself failed, rather than the mounting:
spsalso
spsalso
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High rise window fail in San Francisco storm 2
- Thread starter spsalso
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I'm not at all surprised by the glass failing; it's a common problem in tall buildings, where stresses build up over time from building settling or movement, and the mounting has only so much compliance. My son lives in a 8 story condo and most of his front facing windows are cracked.
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Is there an issue with tempered glass slowly relaxing the built in stresses over time, since glass is considered a 'supercooled' liquid. I understand some medieval stain glasses have 'flowed' a tad, and created an opening (Myth... see below).
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That's a myth
Tempered glass is probably even less likely to flow, given the amount of internal stress it has.
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As the article indicates, glass is not a "supercooled fluid", but an amorphous solid, i.e., it has no general or pervasive crystalline structure, but has, relatively small domains of crystallinity. The bottom line is that glass, tempered or otherwise, basically doesn't change, on the order of centuries, if not millenia. It's no different than, say, Damascus steel, in retaining its mechanical properties. It's by far more robust than Teflon, which actually does flow under pressure.
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Alistair_Heaton
Mechanical
As a teenage summer job I worked for a glazing company. AC Yule in Aberdeen and its still quite surprising seeing jobs I worked on 35 years ago still looking good.
The safety glass you could throw bowling balls, hammers what you like at it in the scrap skip and they would just bounce out. If you wanted to break it to get more in the skip you just tapped the edge with a toffee hammer and the whole lot would go.
Its something to do with the result of the tempering process.
Glass does change over time, normal glass pre tempering you have about 1-2 years after manufacturing to cut it or form it. After that it gets much more brittle and unworkable in a cold state. If its been processed/treated it is of course unworkable.
A can't give a reference to it, its just experience.
Oh there is a rod of glass in either the science museum or one of the UK classical university's which is suspended horizontally between 2 supports which has a bit of a visual sag in the middle. Its 300-400 years old and the sag is mm over a 3ft length.
We had a lecture on glass in materials, from memory the modern stuff is completely different to the pre WW2 stuff which quite a lot of it is in modern standards higher than acceptable radioactive.
And to note there are glass instruments of the same era as the rod and there is no noticeable or measurable changes and they include optical glassware.
Not that it will be a factor in this case.
I suspect the window has flexed in its mount and moved over the years to get the edge into contact with something, maybe a screw head not put in flush, hard enough to trigger the self destruction mode of a side tap to the edge.
Glass is amazing stuff. We only got 1 lecture on it and the summary was its doesn't work the way you think it should, but its amazing stuff.
The safety glass you could throw bowling balls, hammers what you like at it in the scrap skip and they would just bounce out. If you wanted to break it to get more in the skip you just tapped the edge with a toffee hammer and the whole lot would go.
Its something to do with the result of the tempering process.
Glass does change over time, normal glass pre tempering you have about 1-2 years after manufacturing to cut it or form it. After that it gets much more brittle and unworkable in a cold state. If its been processed/treated it is of course unworkable.
A can't give a reference to it, its just experience.
Oh there is a rod of glass in either the science museum or one of the UK classical university's which is suspended horizontally between 2 supports which has a bit of a visual sag in the middle. Its 300-400 years old and the sag is mm over a 3ft length.
We had a lecture on glass in materials, from memory the modern stuff is completely different to the pre WW2 stuff which quite a lot of it is in modern standards higher than acceptable radioactive.
And to note there are glass instruments of the same era as the rod and there is no noticeable or measurable changes and they include optical glassware.
Not that it will be a factor in this case.
I suspect the window has flexed in its mount and moved over the years to get the edge into contact with something, maybe a screw head not put in flush, hard enough to trigger the self destruction mode of a side tap to the edge.
Glass is amazing stuff. We only got 1 lecture on it and the summary was its doesn't work the way you think it should, but its amazing stuff.
Alistair_Heaton
Mechanical
just some links. Annealed is the other state I forgot. If it has come down in larger panels it will be that instead of tempered. I think UK you have to use laminate safety glass above a certain height in building's to stop a shower of glass shards.
JohnRBaker
Mechanical
If you look at the videos, it appears that the glass panels didn't disintegrate until they hit the ground. In the air, they were still large, single pieces of glass. And if you look in one shot, it showed a window with only a portion of the glass missing, like a chunk broke out, away from the rest of the window which was still in the frame.
John R. Baker, P.E. (ret)
Irvine, CA
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John R. Baker, P.E. (ret)
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Alistair_Heaton
Mechanical
that Pilkington link has the links to the UK codes on the subject I think.
UK though did change things after the PIRA bombing in London which basically blew out all the windows in the area.
I am no expert but if its big shards then it just annealed plain glass not tempered I think.
UK though did change things after the PIRA bombing in London which basically blew out all the windows in the area.
I am no expert but if its big shards then it just annealed plain glass not tempered I think.
Tempered glass is usually only installed if there is significant risk of being hit, such as with floor level panes
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Alistair_Heaton
Mechanical
No clue all the stuff I was involved with was either double glazing units or Cordonas bowling alley in Aberdeen with single pane stuff and that we had great fun trying to break in the scrap skip until someone nearly got brained by a bowling ball lobbed off the roof and bouncing.
An interesting article about the type of glass used in modern high rise buildings. Heat strengthened glass seems to be the norm. I thought it clever that they include a few marked panels of tempered glass to allow firefighters to break in.
Alistair_Heaton
Mechanical
UK the firemen have a tungsten carbide tipped bolt gun that breaks them. Bit like the emergency hammers on trains but on steroids. They use it on car windows as well.
They press the front on which pushes back a safety interlock and they can release the spring.
They press the front on which pushes back a safety interlock and they can release the spring.
JohnRBaker
Mechanical
I carry a tungsten-tipped tool in my car to break the windows. It also has a blade to cut your seat-belt. And yes, I keep it where I can reach it at any time. And there's a second one in my wife's car, also where it can be easily reached.
John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:
The secret of life is not finding someone to live with
It's finding someone you can't live without
John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:
The secret of life is not finding someone to live with
It's finding someone you can't live without
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