Graduate Schools and Colleges

"A Tall Order"

Without civil engineers, skyscrapers, power plants, and other major construction projects could never get off the ground.

By Mary Kathleen Flynn

Civil engineers are often the unsung heroes of their projects. "The fame may go to the developer and the lead architect," explains Jack Klein, vice president of construction for Silverstein Properties, the developer for the 7 World Trade Center site. "But the civil engineer raises the structure. And the structure is the most important part of the building. Without the structure, we can’t hold up the architect’s design." Civil engineers specialize in huge projects such as bridges, dams, harbors, power plants, airports, and skyscrapers, and they assume a wide variety of roles in bringing these complicated and demanding projects to life. Civil engineering involves site investigations and feasibility studies, structural design and analysis, construction, and facilities maintenance.

As 7 World Trade Center rises like a phoenix out of the ashes of the Sept. 11, 2001, attack, there are literally hundreds of civil engineers hard at work on the new skyscraper. To get an idea of the complexity of the project, consider that the construction documents for 7 WTC include 3,000 pages of specifications and 1,200 pages of architectural, structural, and mechanical drawings. The project has already generated 70,000 documents.

Civil engineers have made major contributions in designing and building the 750-foot skyscraper, which was the last building of the old WTC complex to fall and the first of the new complex to go up. For example, civil engineers specializing in utility layouts worked on the street grid plans to indicate how utilities come in and out of the building. Utilities are essential for any building, but in 7 WTC, they have added significance: The Consolidated Edison substation that powers all of lower Manhattan is located on the ground floor.

Civil engineers contributed to the building’s foundation, as well, analyzing ground conditions. As they examined the soil and rocks, the engineers looked for particular qualities that affect the design of a foundation. "Looking at the ground, including the location, the depth and the dip, tells you how to build what supports the structure," Klein explains.

Because the basement of 7 WTC is three-fourths underwater, civil engineers designed a “bath tub” to hold water outside the structure. They examined the waterproofing detailing and determined how thick the walls had to be to withstand the water pressure.

Civil engineers also conducted wind tunnel studies on 7 WTC, making a physical model of the building equipped with sensors. They then blew air on it, simulating the Manhattan environment to see how the building would react in various wind conditions.

The sheer walls of 7 WTC are made of a 2-foot concrete structure, encasing 70 tons of reinforced steel per floor. Civil engineers designed these walls to resist building movement, taking into account that three cranes would be on top, swinging heavy loads during the construction. Civil engineers further helped determine floor loading—how much weight is likely to be on each floor when the building is occupied.

Given its history, 7 WTC has been designed to be "terrorist resistant." Civil engineers specializing in blast engineering developed ways to harden the building to ensure that the skyscraper could stand up against any attack.

While this elegant blue-tinted skyscraper represents an important rebuilding of the World Trade Center in New York City, it also serves as a model for future tall buildings and innovative engineering design.

Content excerpted from ENGINEERING, GO FOR IT!
with permission from the American Society for Engineering Education.
For more on the publication in which these articles appear, please go to:
www.engineering-goforit.com.