Message #119972

[Jeannette Latoria]

1973: World Trade Center Is Dynamic Duo of Height

When they debuted in 1973, the two glistening 110-story towers of New York City's World Trade Center (WTC), 1,362 and 1,368 ft high, were more than 100 ft taller than the city's other world height record holder—the Empire State Building. Their size was the subject of a joke during the press conference to unveil the landmarks. WTC architect Minoru Yamasaki was asked: "Why two 110-story buildings? Why not one 220-story building?" His tongue-in-cheek answer: "I didn't want to lose the human scale."

     Before foundation excavation began, the 500 x 1,000-ft site was enclosed by a 3-ft-thick, 70-ft-high concrete cutoff wall built by the slurry trench wall method and keyed 3 ft into rock. Excavation was complicated by two nearby subway tubes that had to be supported without service interruption. A six-level basement was built in the foundation hole. Excavation of 1.2 million cu yd of earth and rock created $90 million of real estate for project owner, the Port of New York Authority. Instead of being trucked off for disposal, spoil was used to create 23 acres of fill in the Hudson River adjacent to the WTC site. It has since been developed as Battery Park City.

     The twin towers had the world's highest load-bearing walls. Seattle-based structural engineer Worthington, Skilling, Helle and Jackson designed them as vertical cantilevered steel tubes. Exterior columns are 14-in. square hollow box sections spaced 39 in. center-to-center. Spandrels welded to the columns at each floor make them into huge Vierendeel trusses. Each tower is 208 x 208 ft with a column-free interior between the outer walls and the 79-ft x 139-ft core.

     Installation of steel for the load-bearing walls was more a problem of logistics than construction (ENR 1/1/70 p. 24). Adjacent city streets were narrow, congested and offered little storage space. Each of the 200,000 pieces of steel had to arrive at the right place at the right time—and for the most part, they did. One of the industry's earliest computer-programmed control systems, which took the owner's engineers six months to set up, helped accomplish this. The twin towers' HVAC system circulates and filters 9 million cu ft of air per minute to more than 9 million sq ft of office space. Air conditioning is provided by a 2.5-acre refrigeration plant at the fourth basement level. Instead of cooling towers, intake and outflow pipes run to the river, only 150 ft away.

     The project involved more than 700 contracts, coordinated and administered by Tishman Realty and Construction Co., New York City. The towers held the height record only briefly. Even as they neared completion, work had begun on ChicagoÕs Sears Tower, which would reach 1,450 ft.



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http://web.archive.org/web/20020611065443/http://www.enr.com/new/A0816.asp