PROJECT PROFILE
Client:
Tacoma Narrows Constructors
Fixed Price
Design-Build Contract Cost:
$615 million
Project Duration:
September 2002—April 2007
Design Duration:
September 2002—
September 2003
Parsons Services:
Initial and final design, engineering support, construction quality assurance,
seismic engineering, bridge type studies, conceptual and final design,
seismic evaluation, and construction engineering
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Parsons has a long, successful history of designing many of the world’s suspension bridges, including the Tagus River Bridge in Portugal. Parsons designed the bridge in the early 60s to receive a future lower level and then designed the lower deck, which was completed in the late 90s. Parsons’ suspension bridge expertise and design-build capability were key factors in its selection as the joint venture lead on the Tacoma Narrows Bridge design-build project, scheduled for fast-track completion in 55 months. In September 2002, Parsons received notice to proceed as the lead engineer responsible for design, engineering support during construction, construction quality assurance, and temporary works engineering for the new Tacoma Narrows Suspension Bridge. We are also upgrading the existing Tacoma Narrows Suspension Bridge and the 2.4-mile roadway approach.
The original 5,939-foot-long Tacoma Narrows Bridge linking Tacoma and Gig Harbor, Washington, opened to traffic on July 1, 1940. Popularly known as “Galloping Gertie,” the bridge earned the nickname from its rolling, undulating behavior. Motorists crossing the 2,800-foot center span sometimes felt like they were riding a giant roller coaster: the cars ahead momentarily disappeared from view as though dropped into the trough of a large wave.
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Left: "Galloping Gertie"the original Tacoma Narrows Bridge. Right: The bridge collapses during a wind storm on November 7, 1940. |
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Acting like a sail, the original bridge deck caught the wind rather than allowing it to pass through. As the wind’s intensity increased, so did Gertie’s rolling, corkscrewing motion—until it finally tore the bridge apart during a 42-mph windstorm only four months after it opened. This disaster was the genesis of wind engineering for bridges: bridge designs are now modeled and tested in wind-tunnels to prevent similar catastrophes. Gertie’s wreckage remains on the bottom of the Narrows and has been declared a national underwater monument.
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Left: Final
instrumentation is checked prior to full bridge aeroelastic wind
tunnel testing at NRC labs in Ottawa, Canada. Right: View of wind tunnel models. |
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The current, much safer Tacoma Narrows Bridge, situated on State Route 16 in Pierce County, opened on October 14, 1950. It is the primary link between the Seattle-Tacoma metropolitan area on the eastern shore of Puget Sound and the scenic residential and recreational areas on the Olympic Peninsula to the west. After 53 years of operation, it has been nominated for the National Register of Historic Places.
In recent years, population and traffic growth have increased congestion along State Route 16, especially on the Tacoma Narrows Bridge. During peak periods, the four-lane bridge operates at or beyond its design capacity. Congestion lasts for three to four hours—during both morning and evening rush hours—costing motorists a significant amount of lost time every year.
The new Tacoma Narrows Bridge, set to open in 2007, is only the second suspension bridge to be built in the United States in the past 40 years—the first was California’s new Carquinez Bridge for which Parsons provided design services and engineering support during construction. The new Tacoma Narrows Bridge is in the top five in the United States in terms of its span, behind the likes of the Golden Gate Bridge and the Mackinac Straits Bridge. Its caissons are some of the largest ever built—they are equivalent to an underwater 20-story building supporting the 510-foot-tall towers. They are being constructed under environmentally extreme conditions—150-foot-deep water, currents up to 7 knots, 50-degree waters, and 50-mph winds are routine.
  Caisson concrete placement for one of the towers. Caissons are currently moored at Port of Tacoma and will be towed to the site later this year. |
To ensure that currents do not erode the soil around the caissons, Parsons performed extensive scour analysis of the channel bottom using field measurements combined with physical modeling to accurately portray the channel bed behavior. Tidal conditions and the existing bridge’s caissons complicated the analysis.
The client challenged Parsons to deliver parts of the caisson design within one month after notice to proceed and to deliver the complete caisson design before completing the superstructure design. We worked closely with both the client and the owner, Washington State Department of Transportation (WSDOT), to make reasonable assumptions regarding the design loads, mitigate risk as much as possible, and still deliver the caisson design early. The entire design will be completed within 14 months of notice to proceed.
Parsons has also performed general and detailed inspections of the existing Tacoma Narrows Bridge to determine the condition of all structural systems, including main cables, suspender ropes, stiffening trusses, towers, foundations, girders, floor beams, stringers, dampers, and bents. The existing bridge will be seismically upgraded and reconfigured to three lanes for westbound traffic.
The new bridge will run south of and parallel to the existing bridge. It will be 5,400 feet long with a 2,800-foot main span and will include three traffic lanes consisting of two eastbound general-purpose lanes and one HOV lane, shoulders on both sides, and a separate bicycle/pedestrian path. The configuration will match that of the nearby 53-year-old bridge. The design can accommodate a second deck for future light rail or additional highway lanes. Other construction includes a toll plaza, access lanes, a new interchange on the west shore, and an additional traffic lane in each direction between the nearest interchanges on each side.
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Left: Cross section of the new Tacoma Narrows
Bridge. |
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Parsons’ numerous value engineering changes eliminated tunnels and saved earthwork, reinforced concrete, and structural steel. An innovative Parsons design alternative reduced the size of the anchorages (which anchor the cables at each end of the bridge) while still accommodating a future lower level through the anchorage block.
For this project, Parsons is performing work in three locations simultaneously: Gig Harbor, New York, and San Francisco. All locations are linked electronically and access files from a common server. We also hold bi-weekly task force meetings on site to unite the owner and contractor with the designer to jointly identify and resolve constructability issues presented by this complex and fast-paced project.
“TNC is proud to see the Tacoma Narrows Bridge Project get off to such a good start. The Parsons-led JV has helped make this possible by contributing as an integrated member of our team. Design leaders have provided the technical guidance necessary to ensure that the main elements of the design move forward in support of our commitments. Leadership provided by the management and the various design leads has been visible throughout the various task force meetings, with a focus on resolving constructability and coordination issues while the design is under development. Their solid technical expertise, professional demeanor, and ability to work effectively within a design-build environment and an 'incentivized' design contract have proven key to our success. And we are certainly looking forward to keeping this positive momentum throughout the rest of the project.
The Parsons-led JV overall performance to date confirms that our decision to make them part of the Tacoma Narrows Bridge Team was the right one."
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Sampling of suspension
bridges on which Parsons has worked. |
Tacoma Narrows is the latest project in Parsons’ long, prolific history of designing suspension bridges. Parsons’ suspension bridge expertise, coupled with its design-build capability, has been a major contributor to the overall success of this project to date. It is the first major transportation design-build project in the state of Washington, and its success is a key component in WSDOT's transportation program.
Visit the Tacoma Narrows Bridge Project website.
