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125 YEARS IN ENR HISTORY: World Trade Center Is Dynamic Duo of Height (8/16/99)

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ENR HISTORY (8/16/99)

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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 Chicago’s Sears Tower, which would reach 1,450 ft.


Contractors Face Fuel Shortages

Contractors Face Fuel Shortages Gasoline shortages that began on the West Coast spread eastward in 1973. Construction firms were forced to rely on independent fuel providers and pay higher prices to keep vehicles and jobs rolling. One San Antonio-based contractor came close to shutting down a highway job for lack of fuel, managing to find some just two hours before supplies ran out. Contractors in other areas experienced delays on jobs until they could negotiate contracts for adequate fuel supplies, and it became increasingly difficult to find distributors throughout the U.S. who were willing to bid on supplying large amounts of fuel. Prices on diesel rose 50% higher than the previous year. A major oil company salesman informed one East Coast construction firm that it might be on a ration system before too long (ENR 4/5/73 p. 11).

Civil Rights in Construction

To some, the 1960s-era civil rights struggle had generated no real progress in construction by 1973 except for "a legacy of tough-sounding legislation and countless assistance programs." One building trades labor affairs director agreed that racial discrimination patterns still existed in unions, but argued that gains were being made in apprenticeship programs. He claimed that at least two outreach programs attracted more than 12,000 minority youths into the industry. But one official of the National Association for the Advancement of Colored People charged that the programs merely perpetuated the illusion that improvements were being made while maintaining the status quo (ENR 5/3/73 p. 17).

Plans to Rebuild Vietnam

A cease-fire in the Vietnam War generated plans for its reconstruction, estimated to cost up to $20 billion (ENR 2/1/73 p. 17). But the U.S. adopted a "wait-and-see attitude" on rebuild programs, while foreign governments cautiously set machinery in motion. Japan was expected to take a major role in rebuilding roads and power networks. The Dutch gave top priority to flood control and irrigation systems, and Sweden was asked by Hanoi officials to provide two 500-bed hospitals. Other countries pledged new aid packages. The Soviet Union agreed to adopt dam-building and power projects as its priority. enr reported that President Richard Nixon would be judged not on what was to happen in Southeast Asia, but on what he did at home to rebuild the "bridges of understanding torn down by the war."


© 1999 Engineering News-Record

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