Analysis of information sources in references of the Wikipedia article "World Trade Center (1973–2001)" in English language version.
From the opening day of the South Tower Observation Deck in December 1975 through close of business on the night of September 10, 2001, more than 46.3 million visitors experienced the views from the tower's summit.
The framed tube, which Khan developed for concrete structures, was applied to other tall steel buildings.
... the loads initially carried by the damaged exterior columns were transferred by Vierendeel truss action to the remaining exterior columns immediately adjacent to the impact area."World Trade Center Building Performance Study". Federal Emergency Management Agency. May 2002. Archived from the original on April 30, 2011. Retrieved August 21, 2019.
Manhattan — John De Smidt is positively insouciant as he and his construction crew climb still higher, erecting a 365‐foot television‐transmission antenna on the roof.
... the loads initially carried by the damaged exterior columns were transferred by Vierendeel truss action to the remaining exterior columns immediately adjacent to the impact area."World Trade Center Building Performance Study". Federal Emergency Management Agency. May 2002. Archived from the original on April 30, 2011. Retrieved August 21, 2019.