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Spanning History

In Washington State, a sleek new suspension bridge could make folks finally forget Galloping Gertie.

By David Einstein
Photographs by Terry Lowenthal/Bechtel

Among construction projects, suspension bridges are special. Elegant and graceful, they connect places, and therefore people. They are built in full view, which gives the public almost parental pride in following their creation. And they often become part of a city or region’s identity, like San Francisco’s Golden Gate Bridge or the Brooklyn Bridge in New York.

Tacoma, Washington, just south of Seattle, also is identified with a famous bridge—one that no longer exists. In July 1940, the first Tacoma Narrows Bridge opened. It quickly earned the nickname Galloping Gertie, because its roadway rolled and undulated in the wind. Four months after opening, it collapsed during a windstorm and sank to the bottom of Puget Sound, making history as the most famous bridge failure of all time (see Wind Tunnel Tested ).

Gertie was replaced in 1950 by another bridge—built on the same foundations. It proved to be stronger, weathering every storm for more than half a century, but it couldn’t handle the increases in traffic that accompanied Tacoma’s growth. Designed to carry up to 60,000 vehicles per day, the bridge now carries 90,000.

Relief is on the way, however, in the form of the new Tacoma Narrows Bridge, which is under construction right next to the 1950 bridge. The two together are expected to handle 120,000 vehicles daily by 2020.

With an overall length of 1,646 meters and a main span of 853 meters, the new suspension bridge will be the longest built in the United States since 1964, when the Verrazano Narrows Bridge opened in New York.

“We’re doing something unprecedented here—building a new bridge less than 20 meters from the foundations of an existing bridge, and atop the ruins of Galloping Gertie,” says Manuel Rondón, Bechtel’s project manager for the new Tacoma Narrows Bridge project. Bechtel, in a joint venture with Kiewit Pacific, is designing and building the $849 million project for the Washington Department of Transportation.

The first major phase of construction—the foundations for the towers—began in the summer of 2003, when two giant caissons, each the size of a seven-story building, were towed into place just south of the existing bridge. Over the course of several months they were slowly filled with concrete and sunk to the narrows floor 46 meters below the surface. It was a challenging job, says Rondón. Workers had to contend with the proximity of the existing bridge, avoid the wreckage of Galloping Gertie (protected as a historical site), and place the caissons precisely using global positioning system (GPS) satellites despite treacherous winds and currents.

The caissons were completed by June 2004. “We had worked every day for a year and nobody saw what we were doing because we built the caissons from the surface of the water down,” says Rondón. That changed dramatically with the start of work on the two towers that give a suspension bridge its signature shape, and by July 2005, they had reached their height of 47 meters above the water. “We almost had to warn drivers on the existing bridge to pay attention to the road and stop looking at the towers,” says Rondón.

Thanks to advances in materials technology, the new towers are made of reinforced concrete, which will require less maintenance than the steel towers of the existing bridge. Another difference—the legs lean toward each other, giving the towers the appearance of a truncated “A.” “We got a lot of calls from people asking if we knew the legs weren’t straight,” says Rondón.

During construction of the caissons and towers, work was completed on the two massive anchorages for the main cables. Each anchorage contains some 18,000 cubic meters of concrete and weighs—are you ready?—40,000 tonnes.

Once the towers were completed in July 2005, work immediately began on the two main cables that will carry the weight of the deck. Each cable is about half a meter in diameter and consists of 19 strands, each composed of 454 galvanized wires. The cables are constructed using automated spinning wheels that pull wires from the east anchorage to the top of the first tower, then to the second tower, and finally to the west anchorage.

After the cables are completed, it will be time to assemble the deck, which is being fabricated in South Korea in 46 sections, most of them 37 meters long. The sections will be shipped to the site, where they will be lifted into place and secured to vertical suspender cables connected to the main cables.

The deck design of the new bridge, like the tower, is different from the existing bridge. Back in the 1950s, decks were usually composed of rigid steel plates. Today, designers of long suspension bridges use lighter steel plates with beams running both lengthwise and crosswise. This lighter “orthotropic” design helps distribute loads, enabling better performance under different loads, temperatures, winds, and seismic movement conditions. The deck itself will be topped by five centimeters of asphalt and concrete.

The new bridge also will feature a truss box below the deck—which will make it easy to add a second deck for traffic or light rail in the future. “That’s something we did successfully in Portugal,” says Rondón, who led a multinational team that added a second deck for a railway to the April 25 Bridge in Lisbon.

Along with construction of the new bridge, the Tacoma project is improving nearly 4 kilometers of roadway on State Route 16 in Tacoma and Gig Harbor, and retrofitting the existing bridge so that both it and the new one will have two lanes for regular traffic and one high-occupancy lane. The new bridge also will have a bike path. Traffic on the existing bridge will go one way westbound, with the new bridge running eastbound.

So far, the new Tacoma Narrows Bridge is on schedule. Bechtel’s Karsten Baltzer, who heads up cable spinning and deck erection, says the reason is simple. “We’re really organized and we have good planning. When we finish one phase, we’ve completed the planning for the next phase. And by emphasizing planning, we ensure we can execute.”

To Rondón, suspension bridges are the aristocrats of bridges. “They are monuments,” he says. “They become a trademark any place you have them.” It’s true. The new Tacoma Narrows Bridge isn’t even finished, and already it’s making folks forget about Galloping Gertie.