Construction crews working the One World Trade Center site reached a milestone on Aug. 12 by placing the largest steel column to date for the $3.1-billion tower in Lower Manhattan. The 60-ft, 70-ton beam will serve as one of 24 perimeter columns that surround the building’s core. Once placed, the columns will allow the initial floors of the tower––including the lobby––to be built out. Tishman Construction is managing construction on the 2.6-million-sq-ft, 102-story structure for the Port Authority of New York and New Jersey. Construction began in April 2006 on the steel-frame tower designed by the New York office of
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.