2008 OCEA Finalist

Header

Tacoma Narrows Bridge, Tacoma to Gig Harbor, Washington

Tacoma NarrowsThe Tacoma Narrows Bridge, the longest suspension span built in the United States in four decades, officially opened to traffic in July 2007. The structure, one of the first major suspension bridges in North America to be delivered under the design/build contracting model, crosses the Tacoma Narrows, in Washington State, to link Tacoma and Gig Harbor. It was designed and built for the Washington State Department of Transportation by Tacoma Narrows Constructors (TNC), a joint venture of Bechtel Infrastructure Corporation, of San Francisco, and Kiewit Pacific Company, of Omaha, Nebraska. TNC retained parsons/HNTB, a joint venture of Parsons Transportation Group and HNTB. Work on the $615-million lump-sum turnkey contract began late in 2002. By that time 90,000 cars a day were crossing the existing bridge, which was built in 1950 and designed to handle 60,000 cars per day.


The new bridge is adjacent to the existing one, which replaced a span that collapsed in spectacular fashion in 1940 just a few months after it opened. The event was captured on film and changed the way suspension bridges are designed. The deck of the new bridge takes the form of a steel truss 5,400 feet (1,646 m) long, the main span being 2,802 feet (854 m) from tower to tower.


Major construction work included installing caissons for two 509 feet (155 m) tall towers, building the towers, spinning cables, and assembling the deck. During the final phase, 46 deck sections – each weighing an average of 459 tons (416.4 metric tons) – were lifted and attached to suspension cables.


Among the challenges that the project team faced were the proximity of the new bridge to the existing crossing; the high winds, strong currents, and tidal changes typical of the Tacoma Narrows; the importance of preserving the pristine environment of the area; and the need to work around the remains of the 1940 crossing, now resting at the bottom of the waterway.