[URBAN NOTE] Negligence or breakage? More on the One Bedford glass fall
Responding at Facebook to my post describing the fall of a panel of glass from the 32nd story of a condo tower near the St. George subway station, Ben--an experienced contractor--had a lot to say. Yes, it's disquieting.
There are two basic designs of glass parapet railing. The more common has slots in extruded aluminum top and bottom rails, with the glass fitting in the slots. The less common has one of various fittings, generally in stainless steel, securing the glass to the posts, such as here:
http://products.construction.com/Manufacturer/Innovative-Structural-Glass--Inc--NST28064/products/Fittings-NST15689-p
But it appears to be the first type here. If so, the most probably errors that would result in a panel coming loose are:
1) The panel was improperly fitted in the rails. This would have been very easy to notice.
2) The glass was slightly undersized, allowing not enough "bite" for the slots in the rails to hold it. If this was the case, the situation is very dangerous, because the odds are that the same condition exists throughout the building.
Here's one I've used on several projects:
http://www.kanescreens.com/images/cad/Chesterfield_System_Full_Image.GIF
You can see it's got the "slotted rails". If it's built correctly, it is impossible for that event to occur.
[. . .]
I was thinking "how did the system fail?" but there is another possibility- that the railings were damaged by abuse. Deliberately jumping on the bottom rail (or otherwise beating on it) could loosen it to the point where the glass panel slips loose. Whatever the case, an experienced forensic civil engineer should be able to quickly tell which actually caused the failure.
One more thing! The glass in railing systems like this is supposed to be tempered. Tempered glass fragments into tiny bits when broken. It should be possible, from evidence, to determine whether the glass was broken at the balcony, and fell as a rain of little bits, or fell as a unit and broke on impact. The former would be consistent with abuse at the balcony, the latter with faulty construction or manufacture.
I wasn't close, but it seemed from the brooms that people were using to sweep the sidewalk that it may have fallen as such a rain of little bits.
There are two basic designs of glass parapet railing. The more common has slots in extruded aluminum top and bottom rails, with the glass fitting in the slots. The less common has one of various fittings, generally in stainless steel, securing the glass to the posts, such as here:
http://products.construction.com/Manufacturer/Innovative-Structural-Glass--Inc--NST28064/products/Fittings-NST15689-p
But it appears to be the first type here. If so, the most probably errors that would result in a panel coming loose are:
1) The panel was improperly fitted in the rails. This would have been very easy to notice.
2) The glass was slightly undersized, allowing not enough "bite" for the slots in the rails to hold it. If this was the case, the situation is very dangerous, because the odds are that the same condition exists throughout the building.
Here's one I've used on several projects:
http://www.kanescreens.com/images/cad/Chesterfield_System_Full_Image.GIF
You can see it's got the "slotted rails". If it's built correctly, it is impossible for that event to occur.
[. . .]
I was thinking "how did the system fail?" but there is another possibility- that the railings were damaged by abuse. Deliberately jumping on the bottom rail (or otherwise beating on it) could loosen it to the point where the glass panel slips loose. Whatever the case, an experienced forensic civil engineer should be able to quickly tell which actually caused the failure.
One more thing! The glass in railing systems like this is supposed to be tempered. Tempered glass fragments into tiny bits when broken. It should be possible, from evidence, to determine whether the glass was broken at the balcony, and fell as a rain of little bits, or fell as a unit and broke on impact. The former would be consistent with abuse at the balcony, the latter with faulty construction or manufacture.
I wasn't close, but it seemed from the brooms that people were using to sweep the sidewalk that it may have fallen as such a rain of little bits.