11 сентября 2001   ::   Мейссан Тьерри

The core consisted of 5-inch concrete fill on metal deck supported by floor framing of rolled structural shapes, in turn supported by a combination of wide flange shape and box-section columns. Some of these columns were very large, with cross-sections measuring 14 inches wide by 36 inches deep. In upper stories, these rectangular box columns transitioned into heavy rolled wide flange shapes (see Appendix B for a picture of the transition from box column to H-column).

Between the 106th and 110th floors, a series of diagonal braces were placed into the building frame. These diagonal braces together with the building columns and floor framing formed a deep outrigger truss system that extended between the exterior walls and across the building core framing. A total of 10 outrigger truss lines were present in each building

Figure 2-10 Outriger truss system at tower roof.

(Figure 2-10), 6 extending across the long direction of the core and 4 extending across the short direction of the core. This outrigger truss system provided stiffening of the frame for wind resistance, mobilized some of the dead weight supported by the core to provide stability against wind-induced overturning, and also provided direct support for the transmission tower on WTC 1. Although WTC 2 did not have a transmission tower, the outrigger trusses in that building were also designed to support such a tower.

Figure 2-11. Location of subterranean structure.

A deep subterranean structure was present beneath the WTC Plaza (Figure 2-11) and the two towers. The western half of this substructure, bounded by West Street to the west and by the 1/9 subway line that extends approximately between West Broadway and Greenwich Street on the east, was 70 feet deep and contained six subterranean levels. The structure housed a shopping mall and building mechanical and electrical services, and it also provided a station for the PATH subway line and parking for the complex.

Above, is a photo of the area shaded in blue, in Figure 2-11 (looking north). In the foreground, are the foundations for the central core of the South Tower. The North Tower can be seen on the left further back. Two subway lines can be seen crossing the site (the two bridge-like structures). The site extended from West Street in the west to the old extention of Greenwich Street in the east (which was ripped up to make way for WTCs 4 and 5) and from Vesey Street in the north to Liberty Street in the south.