"Matt Mc_Carthy" wrote to "MIKE ROSS" (20 Dec 02  00:39:13)
 --- on the topic of "Word Trade Center"

 MM> Hit the nail on the head!  The structural component of the WTC was the
 MM> central core of steel.  Ordinary old buildings that demolitions people
 MM> normally work with have basically "four legs", and if the timing is
 MM> off allowing any one leg to 'fail' too soon, the building falls
 MM> sideways.
 MM> The central core is like dropping donuts on a horseshoe pole, they can
 MM> only go straight down.

The older buildings were made up of many little steel cubes all linked
together to form a larger structure. The problem with that system is one
couldn't have a wide open space without columns in the middle of it.
There was also a matter of resources and economics to build such
buildings beyond a certain height.

The genius of what the engineers did in the case of the WTC was to move
the columns to the outer walls and central core so that the floors were
held up between the two, like a bridge using trusses. The whole outer
shell of the WTC was made of thick structural steel sheets bolted
together. In fact that was the only structure seen sticking out like a
crown from the rubble.

In one building it was the core which failed first and in the other it
was the outer wall. Both outcomes were affected by the way in which the
inpacts were directed, since one mostly missed the core but did more
damage to the walls and one struck the core dead on but with much less
fatal damage to the supporting walls.

In either case the burned sagging floor joists, which pulled both
support structures upon one another, when their connecting end links
broke, the walls promptly buckled like a house of cards falling down.
The intact remaining floors above completed the pancake effect by acting
as a giant pile driver mass. It was a sad combination of circumstances.

 Mike
 ****

... Pentium wise; pen and paper foolish...
--- Blue Wave/DOS v2.30