ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/740919
PROJECT SR 520 Evergreen Point Floating Bridge East Approach Bridge Greg Banks, BergerABAM, and Dellas Clark, Kiewit-General-Mason Nestled between Seattle, Wash., and the nearby communities of Bellevue, Kirkland, and Redmond, is the nearly 50-mi.-long, more than 1-mi.-wide, majestic Lake Washington. Recent population growth in these communities has brought an increase in transportation demands on the corridors connecting them with Seattle. Washington State Route 520 (SR 520) serves as one of two corridors crossing over Lake Washington. Designed with only four traffic lanes, two in each direction, the nearly 50-yearold existing floating bridge is often clogged with heavy traffic. The aging infrastructure was also vulnerable to windstorms that required closure of the corridor due to waves crashing onto the roadway, and had seismically vulnerable approach spans that failed to satisfy current seismic design code standards. Due to these deficiencies, the Washington State Department of Transportation decided to release a design-build contract to construct a new floating bridge across the lake. The new bridge would include two generalpurpose lanes and one high-occupancy lane in each direction, plus full shoulders on an elevated roadway deck; a regional shared-use path; and means to accommodate high-capacity transit at a future date. The new SR 520 Evergreen Point Floating Bridge is made up of a number of elevated bridge segments: the pontoonsupported low-rise and high-rise structures; single-span structures at each end of the pontoons providing transitions from the floating bridge segments to the land-based fixed segments; Pier 36 (two-column/shaft land-based fixed pier marking the west end of the contract); and the focal point of this article, the land-based, fixed, east approach bridge. Comprising twin three-span, parabolicarch shaped, cast-in-place concrete box-girder superstructures, one for westbound and one for eastbound traffic, the east approach bridge structures provide an elegant transition between the land-based fixed structures and the low-profile floating bridge structure. The overall length of the east approach bridge is 630 ft, with a cantilever span of approximately 110 ft, an interior span of approximately 320 ft, and an end span of approximately 200 ft. The 110-ft cantilever span supports the end of a 190-ft-long transition span structure whose other end is supported on the floating bridge. Together, the transition span and cantilever end of the east approach bridge create a nearly 300- ft span forming the lake’s east navigation channel. PROFILE SR 520 EVERGREEN POINT FLOATING BRIDGE EAST APPROACH BRIDGE/SEATTLE AND MEDINA, WASHINGTON BRIDGE DESIGN ENGINEER: BergerABAM, Federal Way, Wash. PRIME CONSULTANTS: KPFF and BergerABAM, partners as the prime engineering team, Seattle, Wash. PRIME CONTRACTOR: Kiewit, General Construction, Manson Construction (KGM)—a joint venture, Federal Way, Wash. POST-TENSIONING CONTRACTOR: Schwager Davis Inc., San Jose, Calif.