>>> Met History <[log in to unmask]> 8/01/00 7:06:16 >>> wrote:
"The gangly-hilarious new Alfred Lerner Hall (replacing the old Ferris Booth) at Columbia has ... The exterior is made up of 10 foot by 10 foot sheets of glass, "floated" to the interior frame in the same way Jim Polshek's firm has done the new Planetarium.  On Lerner Hall, nearest Broadway, there's the largest example of safety glass failure I have ever seen, truly impressive - perhaps caused by a frosted student.  What is the theoretical range of such crumbly-cracking?  A mile?"

Uh oh!

I can feel a long-range failure diagnosis coming here.  This will beat (by many miles) my forensic architect mate Peter Hartog (of the hills) who was (mis)quoted as having claimed that he could identify nickel sulfide inclusions from 50m.

... 10' x 10' glass panes, floating off the structure (point fixings at the corners, I guess)?
... safety glass, with crumbly cracking?
... one failure?

Sounds to me like a piece of tempered glass which when it fails, crazes into little dice.  Now, this could have been caused by lots of things.  Such as impact, edge damage, loading from adjacent panels, lateral loads ... but I'm going to hazard a guess that it was due to a microscopic sized defect in the glass called a nickel sulfide inclusion.

If I'm right, the failure would have initiated (started) in the body of the panel (i.e. away from the edges), and this would be identifiable by a radiating crack pattern from this point.  At the point, would be two slightly larger particles, roughly symmetrical.  There would be a straight fracture plane between the two particles.  And roughly midpoint along that fracture plane, within the thickness of the glass, a small black dot (about 0.1-0.2mm diameter) would be present.  Don't get me started on why this happens - unless you want a very long post!  Suffice to say I've been doing expert witness reports on this type of failure over the last couple of months.

One of the characteristics of this type of failure is that it often starts 18-24 months after installation, and then continues for many years.  Such failures have been quite widespread throughout the world, but are buried by the glass suppliers/installers, who blame many other causes.  Tough to identify, tougher to prove.  One piece of glass doesn't prove the case.  And I have seen an impact failure of tempered glass which looked almost identical to what I have described above ... except that the inclusion (the little black dot) was missing.

Most unlikely that one of the frosted students frosted the glass ... but of course it might just have been one of those stray bullets that roam the NYC streets day and night!

Cheers

david