On 01/08/2017 04:32 PM, Zenaan Harkness wrote:

excessively reinforced central column

   ...and floor supports at the corners but NOT in the middle of the spans
   on the building's outside edges. So when the buildings had  torsionally
   flexed a few times too often as it WAS NOT designed to do, the corner
   supports let go and the floors slid down the central support column.
   Thanks for pointing out why the two WTC towers collapsed straight down.
   Rr