text: Each of the individual stilts is composed of four vertical beams; the outer pairs of beams are much heavier than the inner pairs. This design prevents the stilt from buckling. Inside the stilts are emergency stairs and mechanical ducts. In 2002, following the September 11 attacks the previous year, one of the stilts was reinforced with blast-resistant shields of steel and copper as well as steel bracing. There is also an octagonal elevator core in the middle of the building, which measures  and carries half of the building's gravity-related structural loads. Beneath the lowest office story, the core contains only elevators, and the emergency staircases are within the stilts.
  Chevrons
  Above the stilts, within the walls, are stacked load-bearing braces in the form of inverted chevrons. Each elevation of the facade has six chevrons, which are eight stories tall. The wind loads from each eight-story tier are transferred into the center of the frame, where  "mast column transports" extend the tower's entire height. The mast columns are  deep at their bases, tapering to  above the 40th floor. The diagonal beams in each chevron are  deep and connect to spandrel panels at the top of each eight-story tier, which are  deep. The tops of each eight-story tier (where the diagonal beams meet the building's corners) do not have vertical columns, thus preventing wind loads from accumulating at the tower's corners.