236th Street NE Cantilevered Sidewalk

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The Stillaguamish Tribe of Indians contracted with Combined Construction of Mukilteo, WA to improve a 1.2-mile corridor of 236th Street NE to make it safer for vehicles, pedestrians, and bicyclists. 236th Street NE carries traffic from I-5 to the nearby Angel of the Winds Casino Resort.

The project included widening travel lanes, adding turning lanes, adding shoulders or bike lanes, and creating an illuminated shared use path for cyclists and pedestrians. In addition, the Tribe made a number of environmental improvements along the corridor including replacing an existing 20-inch culvert, classified as a fish barrier, with a new 18-foot wide arched culvert.

Instead of building wide embankments to support the additional lanes and shoulders the designers used retaining walls to minimize the impact to the wetlands along the route. A walkway cantilevered off the south side retaining wall enables pedestrians and cyclists to safely pass over the stream without disturbing the ecosystem.

The 10’ wide x 417’ long cantilevered walkway was built using lightweight FiberSPAN™ FRP panels supported on steel beams spaced 10’ apart. The steel beams were anchored to a concrete ballast block with four post-tensioned bars. The 6” thick deck panels spanned 10 feet between support beams and were designed for 100 psf live load. The molding division of Creative Composites Group supplied a total of 15 panels for the project. The typical panel was 10’ wide x 30’ long  and weighed less than 4,000 lbs. Panels were cross-sloped to facilitate drainage and railings were mounted directly to the tops of the panels.