May 1, 2017

SR 520 floating bridge named top engineering achievement for 2017

Photo from WSDOT [enlarge]

The bridge was one of 162 projects worldwide vying for the ACEC’s top award.

Photo by Magnusson Klemencic Associates/Michael Dickter [enlarge]

The Elliott Bay Seawall Habitat and Public Space won an ACEC Grand Award.

Seattle's 1.5-mile SR 520 Floating Bridge won the American Council of Engineering Companies' Grand Conceptor Award as the year's top engineering achievement.

Two Seattle projects won Grand Awards from ACEC: Elliott Bay Seawall Habitat and Public Space by Magnusson Klemencic Associates, and University Link Extension by McMillen Jacobs Associates on behalf of Northlink Transit Partners. Go to http://tiny.cc/p02tky and http://tiny.cc/f12tky for more information about them.

The Sellwood Bridge Replacement in Portland by T.Y. Lin International also won an a honor award. More information is at http://tiny.cc/m32tky/.

The new SR 520 Floating Bridge is a Washington State Department of Transportation project. WSDOT said it was one of 162 projects worldwide vying for the top engineering award.

HDR was the general engineering consultant on the SR 520 program. Kiewit/General/Manson was the floating bridge's design-builder and KPFF Consulting Engineers was lead design consultant.

The bridge opened to traffic on April 25, 2016, and is the world's longest floating highway span, at 7,708 feet, WSDOT said. The old bridge on Lake Washington opened in 1963, and was 130 feet shorter.

Lake Washington's extreme depth and soft lakebed required construction of a floating bridge rather than a conventional fixed bridge. The new bridge is supported by more pontoons than the old bridge, and WSDOT said it is designed to withstand much stronger windstorms and waves. It also has bus/carpool lanes in both directions and a cross-lake bicycle-pedestrian path. The design allows it to be retrofitted for light rail in the future, WSDOT said.

In a press release, ACEC said the superstructure is supported by 21 of the heaviest, widest and deepest longitudinal pontoons ever built, each weighing nearly 11,000 tons. It is further stabilized by 54 supplemental pontoons, as well as cables and anchors. The bridge is built to resist winds of up to 98 miles per hour and 6.3-foot wave heights, or the equivalent of a 100-year storm.

WSDOT said that when reconstruction of the entire SR 520 corridor is complete, the bridge and connecting highway will carry about 10 percent more vehicles and 17 percent more people during peak traffic hours, while reducing rush-hour, cross-lake commutes between Seattle and Bellevue by about half an hour.