Posted by Paul Dremann on September 14, 2002 at 06:31:22:
Before I desist from talking about the WTC disaster I would like to leave you with a few thoughts.
For those who are curious about viscoelastic dampers you can go to GOOGLE and search for that heading, i.e. viscoelastic dampers. Also, search under 'damped structures in north america'. There you can find the list of buildings containing them and in what numbers.
To reiterate, in the WTC the devices were located on the 'bottom chord' of most of the floor trusses from the 10th to the 110th floors. (refer to Nguyen's drawings, also in GOOGLE). Remember, they were designed as non-structural components that absorbed and dissipated energy during the building's relative motion. The bitumen rubber compound (BRC) was covered by fireproofing material. It has been established that the crash stripped the fireproofing from certain chords where it separated after the bitumen burned, thus 'degrading the integrity' of the trusses. When the lower chord was released from connection the total truss deflected. Lastly there 10,000 devices per tower.
Other similar buildings are Columbia Sea First and Two Union Sq. in Seattle. The Sears Tower,and John Hancock Center, all variations of the Fazlur Khan type 'tube system' buildings.
Enough about the structure of WTC Towers! Pray we 'learn' from this disaster.
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