Core Denial
Establishing the true nature of the core structures is of great importance given that the most widely read document on the World Trade Center attack -- the 9/11 Commission Report -- denies their very existence, claiming the towers' cores were "hollow steel shaft[s]:"
For the dimensions, see FEMA report, "World Trade Center Building Performance Study," undated. In addition, the outside of each tower was covered by a frame of 14-inch-wide steel columns; the centers of the steel columns were 40 inches apart. These exterior walls bore most of the weight of the building. The interior core of the buildings was a hollow steel shaft, in which elevators and stairwells were grouped. Ibid. For stairwells and elevators, see Port Authority response to Commission interrogatory, May 2004. 1
http://911research.wtc7.net/wtc/arch/core.html
The top illustration indicates what may have been typical dimensions and thickness of the smaller core columns, about half-way up the tower. The outermost rows of core columns were apparently considerably larger, measuring 54 inches wide.
Columns
The core columns were steel box-columns that were continuous for their entire height, going from their bedrock anchors in the sub-basements to near the towers' tops, where they transitioned to H-beams. Apparently the box columns, more than 1000 feet long, were built as the towers rose by welding together sections several stories tall. The sections were fabricated by mills in Japan that were uniquely equipped to produce the large pieces. 2
Some of the core columns apparently had outside dimensions of 36 inches by 16 inches. Others had larger dimensions, measuring 52 inches by 22 inches. 3 The core columns were oriented so that their longer dimensions were perpendicular to the core structures' longer, 133-foot-wide sides. Construction photographs found at the Skyscraper Museum in New York City indicate that the outermost rows of core columns on the cores' longer sides were of the larger dimensions. Both the FEMA's World Trade Center Building Performance Study and the NIST's Draft Report on the Twin Towers fail to disclose the dimensions of the core columns, and the NIST Report implies that only the four core columns on each core's corners had larger dimensions.