Posted by d on September 13, 2002 at 11:49:18:
In Reply to: Re: The Price of Progress posted by Paul Dremann on September 13, 2002 at 10:20:54:
You might look back almost precisely one year to the trenchant observations of Ngon Nguyen on this forum, who pointed exactly in the direction that you are, to the defects of the damping system.
At that time, it seemed that the collapse was thus to a significant degree a result of either (or both) failure of the VED connections from mechanical separation or by melting....
However, I don't know that the comprehensive engineering analysis of the experts even mentioned these dampers as a partial cause.
Nevertheless, the general concern seems valid, and is a familiar situation to engineers.
The vast scale and sway of the buildings required flexibility at the connections; yet flexibility implies susceptibility to oxidation failure, whether slowly (as with the Mianus bridge collapse) or quickly (as may have been the case with the dampers).
As I saw it, the critical question was; would any large fire in the upper floors of the WTC (not just the actual attacks) have had the same tragic result? If so, then it would seem that the necessary redundancy was forgotten, ignored or delayed...
The Mianus bridge is sometimes mentioned as an example of the failure to provide redundancy at connections, with ledges etc.
Ngon Nguyen pointed out, in one of his postings, that had the rigid truss/wall connections been true hinges, the fracturing of the connection might have been avoided...
Is this the result of the long-term transformation of mechanical
connection (boltings, rivets, etc) to chemical forms of adhesion?
Should the two be used in tandem, to provide redundancy where critical
systems are connected?
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