Hancock Tower Window Failures

[JayHancock]

Hi all,

Not sure where to put this question but here it goes.

I work in the upper floors of the Hancock Tower. Today a window "failed" (i.e. broke in place in about a million pieces). Last week, a window just one floor below did the same thing.

My question is, is this common? I know this is completely unrelated to the window issues of the 1970's, but does anyone have anymore insight into this?

 

[datadyne007]

Oh my God... that's terribly scary. No, it's not common at all. Windows in high rises are not supposed to shatter... ever. I haven't even seen anything about it in the press. They must be trying to keep it hush hush.

 

[JayHancock]

Granted, they are not falling out onto the street below. Just shattering in place with a tremendously loud pop

 

[datadyne007]

Granted, they are not falling out onto the street below. Just shattering in place with a tremendously loud pop

It sounds like a pressurization issue. An audit of the sealant/caulking probably should be done on the windows immediately. We've had some really violent weather in the past few weeks with intense wind loads being exerted on skyscrapers.

 

[Arlington]

I'm pretty sure this is reasonably common in tempered glass. Common enough that PPG has a page (complete with video) devoted to it on spontaneous breakage. The same tension that makes it strong makes it vulnerable to small inclusions or scratches in the tension layer, which is why it typically either laminated or covered with a film to hold things together if a pane breaks this way. They try to pre-stress all panes to have the flawed ones break at the factory, but they say that temperature changes or building flexing can cause failure when combined with an undetectable flaw.

This recently happened in one (of five) layers in the floor of one of the glass ledge "bump outs" on the Willis Tower in Chicago

 

[datadyne007]

I'm pretty sure this is reasonably common in tempered glass. Common enough that PPG has a page (complete with video) devoted to it on spontaneous breakage. The same tension that makes it strong makes it vulnerable to small inclusions or scratches in the tension layer, which is why it typically either laminated or covered with a film to hold things together if a pane breaks this way. They try to pre-stress all panes to have the flawed ones break at the factory, but they say that temperature changes or building flexing can cause failure when combined with an undetectable flaw.

This recently happened in the floor of one of the glass ledge "bump outs" on the Willis Tower in Chicago

Interesting. The storms probably did have something to do with it...

weakens the glass during high winds

The Hancock is already ridiculously vulnerable to high winds when there aren't violent storms happening.

 

[Arlington]

...in the upper floors of the Hancock Tower. Today a window "failed" (i.e. broke in place in about a million pieces).

Did it, in fact, look like the one on the left, below?

Today I Learned that tempered glass has to be cut before being tempered because the edges are a key part of the structural-tension system, and that you don't want to knick the edges or try to drill a hole in it (the way you can with float glass).

So if there is a scene in Mission Impossible: Ghost Protocol where he scribes a circle in the window of the Burj Dubai, (as I seem to recall), well, the crowds in Pittsburgh would have been throwing stuff at the screen, complaining of tempered glass being inauthentically portrayed.

 

[Downburst]

^I was under the impression that the cracking observed in the Willis Tower glass was the coating/film on the glass Arlington described and not the glass itself. I hope the same is true of any glass on the Hancock.

Also, for what it's worth...

From time to time in Copley square I notice the edges of some panes catching the light differently than others as I line up with the narrow end of the building. Are these broken panes as well?

 

[JayHancock]

Did it, in fact, look like the one on the left, below?

Today I Learned that tempered glass has to be cut before being tempered because the edges are a key part of the structural-tension system, and that you don't want to knick the edges or try to drill a hole in it (the way you can with float glass).

So if there is a scene in Mission Impossible: Ghost Protocol where he scribes a circle in the window of the Burj Dubai, (as I seem to recall), well, the crowds in Pittsburgh would have been throwing stuff at the screen, complaining of tempered glass being inauthentically portrayed.

It looks identical to the picture on the left, and this happened to both panes (today and last week). It's pretty visible on the west-side of the building as well, particularly from the corner of Stuart and Trinity Place

 

[Arlington]

^I was under the impression that the cracking observed in the Willis Tower glass was the coating/film on the glass Arlington described and not the glass itself. I hope the same is true of any glass on the Hancock.

I think the Willis spokesperson didn't understand the concept of "lamination" so the best they could come up with was "coating" instead of "one of the layers in a sandwich of tempered glass".

Either that, or Willis purposely taking a shortcut (rather than explain the engineering) to make it sound less scary.

 

[Downburst]

I think the Willis spokesperson didn't understand the concept of "lamination" so the best they could come up with was "coating" instead of "one of the layers in a sandwich of tempered glass".

Either that, or Willis purposely taking a shortcut (rather than explain the engineering) to make it sound less scary.

Makes sense. Cracking glass does not make for a popular tourist attraction.

 

[Arlington]

Makes sense. Cracking glass does not make for a popular tourist attraction.

It is clear that at Willis there is a "non-structural" layer that sits on top of the structural laminate (that has metal fasteners holding it together). But given how it shattered (in tiny bits) and how they handle it (in picture below) it sure looks like tempered or hardened glass

http://www.parkrecord.com/ci_25864040/cracks-appear-ledge-at-chicagos-willis-tower Looks like when they are removing the old layer, they're carefully brushing out broken glass (with what look to be paint brushes)...not taking out a plastic sheet (and I note that they never say "plastic coating", they're just trying to emphasize that the glass that broke isn't *the* glass of the structure).

You can see that it is layers of glass(es) in this edge view, with the structural laminate's layers visible at all the edges, but then an extra sheet of glass as "carpeting" on the floor:

 

[Randomgear]

I used to live in the South End, just off the Southwest Corridor Park on Greenwich Park. I had a view of the Hancock on the way to work every morning for seven years, between 1997 and 2004. Occasionally, there would be a breakage, probably three or four times in that period. Since my view was always looking Northeast, I only had a view of the south and west sides.. I tend to think that it goes back to the problems that were almost completely, but not quite, solved from the original windows that had major breaking problems. I don't remember windows on the edges breaking, so I don't think that it's a wind load issue (wind loads tend to be highest at the corners).

I also don't know what the makeup of the glass is - whether it's an insulated glazing unit with an air (or insulating gas) space between the glazing layers or just a thick panel of laminated glass. I tend to think that it's the former and it may be composed of two or more layers of heat strengthened glass, annealed glass or fully tempered glass. Seal failure is not uncommon in Insulated Glazing Units but normally all it does is cause the glazing unit to become permanently fogged.

I admit, that I have no access to secret documents (or friendly talkative glaziers) that might tell us what's actually going on.