Only the interior core columns remain standing from about the 60th floor down. What happened to the much stronger outer core columns all the way down?
I'm sorry, I'm not clear on what you are asking. Which "outer" columns are you referring to. From what I understand, the WTC was constructed with a "box within a box" design. The inner core of columns supported half the weight, and the entire outer "skin" of the building supported the rest. This allowed for no interior columns within all the rented space, "opening" it up and allowing for more rentable space. As far as I know, there were no outer columns. Please elaborate.