BRIDGES: First of new S.R. 520 bridge pontoons set to float out July 23

Six completed segments will help support world’s longest floating bridge

Bridges News WSDOT July 20, 2012
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The first six concrete pontoons to support a replacement S.R. 520 bridge in the state of Washington are ready to float out of a construction facility in Tacoma starting Monday, July 23, marking a major milestone toward replacing the aging and vulnerable floating bridge.


Crews will tow pairs of pontoons out of Concrete Technology Corp. on high tides the evenings of July 23, 24 and 25. Pontoons will go through watertight inspections nearby at the Port of Tacoma and be readied for the next round of construction.


“Construction crews have worked for months to build these pontoons, and seeing them float out and towed to Lake Washington this summer will be a huge accomplishment,” said Julie Meredith, S.R. 520 program director for the Washington State Department of Transportation. “We still have a lot of work ahead of us to deliver a new, more reliable floating bridge—and it all starts with pontoons.”


The completed pontoons are the first of 77 of various sizes needed for a new six-lane floating bridge. Together they will help form what will be the world’s longest floating bridge at 7,710 ft. A total of 44 pontoons will be built in Tacoma and 33 in Aberdeen. As each cycle ends, crews prepare the pontoons for assembly in the new floating bridge just north of the existing bridge.


Crews in Tacoma worked for about six months to build this batch of six supplemental stability pontoons. These smaller pontoons will attach to the sides of larger new pontoons to provide additional floatation for the bridge structure. The 44 smaller pontoons each weigh 2,500 to 2,820 tons and measure 100 ft long, 50 to 60 ft wide and about 28 ft tall.


In June, there were 155 workers at the Tacoma jobsite, including 100 craft workers, such as carpenters, ironworkers, concrete workers and equipment operators. Employment levels are expected to rise to meet construction demand as future pontoon construction cycles get under way. Construction is expected to continue into 2014.


“The next few construction cycles in Tacoma build eight pontoons at a time, and this jobsite will continue to buzz with activity for the next two years,” said Dave Becher, WSDOT construction manager for the floating bridge project.


In Aberdeen, crews are completing the first six of 33 pontoons that will form the backbone of the new floating bridge. Pontoons were repaired in June and July after cracks were discovered, and crews are preparing to float them into Grays Harbor and tow them to Lake Washington this summer. A peer review panel is examining the cause of the cracks and preliminary recommendations are pending.


Information about Tacoma pontoon float-out activities July 23 through 25 can be tracked online at


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