The buildings were, tube in tube construction, with cross strcutures between
the tubes, in the case of the first collapse, the fire weakened inner
tube structure collapsed, and the collapse was inwards. Sort of looked
more like an implosion. The other tower appeared to collapse differently.

I heard the fire cladding around the steel structures was 50mm concrete
can anyone confirm this?  Obviously the fire rating was not sufficient
to handle the heat from the burning fuel, but would have been more
than adequate for "normal" fires.

Either way, it's a tradgedy, I don't think you can blame the engineers
in the 70's who designed it for not forseeing this kind of situation.

>
>On Wed, Sep 12, 2001 at 07:42:21PM -0400, Dan Michaels wrote:
>> Chris Pringle wrote:
>> >I was quite interested to hear from one of our structural engineers earlier
>> >today. Apparantly it wasn't the aircraft that caused the buildings to
>> >collapse. The buildings were designed to take the hit of an aircraft.
>> >
>> >What brought the buildings down was the fire. The buildings hadn't been
>> >designed to survive a fire. When the structure became warm, the steel
>> >supports were no longer strong enough to support the weight of the building
>> >and so it gave way.
>> >
>>

Ray Gardiner ray@dsp.com.au
[ 2001 ]

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