THE CONCRETE BRIDGE MAGAZINE

WINTER 2014

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.

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Lightweight concrete deck bulb- tee beams with a lightweight overlay erected on steel piling and bents. Photo: Washington State Department of Transportation. A C C E L E R AT E D B R I D G E C O N S T R U C T I O N I-5 Skagit River Bridge Collapse and Rapid Replacement by Tom Baker, Dr. Bijan Khaleghi, Todd Harrison, Patrick Fuller, and Rich Zeldenrust, Washington State Department of Transportation On May 23, 2013, the evening commute was just ending along a four-lane stretch of the Interstate 5 (I-5) corridor between the Canadian border and Seattle. At roughly 7 p.m., a semitruck heading south and carrying a permitted oversized-load struck the first portal and several subsequent sway members along the steel truss section of the I-5 Skagit River Bridge. The northern truss span of the bridge collapsed into the Skagit River. While the semi-truck made it across, several vehicles didn't and the occupants had to be rescued. Fortunately, no one was killed in the collapse. The Washington State Patrol, the Washington State Department of Transportation (WSDOT), and local agencies responded immediately, setting up and manning detour routes both east and west of the bridge. WSDOT immediately responded with bridge engineers to assess the damage and begin plans for both emergency and permanent repairs, while communication staff responded to the media, and sent out updates and freight alerts region- wide. Traffic engineers worked through the night to refine the detour routes for the roughly 71,000 vehicles that were detoured through the city streets of Burlington and Mount Vernon. Within 24 hours, a contractor was hired under an emergency contract to remove the collapsed span, and began working with WSDOT engineers to install a temporary span to get the interstate back open. As the work was being done to temporarily restore I-5 traffic, WSDOT engineers began assembling contract documents for a permanent span repair. Bridge Type Selection Hours after the collapse, discussions were underway at WSDOT about how best to replace the collapsed span, and how to restore traffic as quickly as possible. Time requirements, vertical clearance requirements, and superstructure dead load limitations quickly became the primary guiding factors in designing the span replacement. Minimizing traffic disruptions dictated the installation of temporary, side-by-side, dual-lane, modular truss bridge spans, which were subsequently replaced with the permanent span. For navigational purposes, vertical clearance to the river below had to be equal to or greater than that provided by the original truss span. And, importantly, to minimize any additional seismic inertial loads to the existing bridge substructure, the dead load of the replacement span could not exceed the dead load of the original truss span by more than 5%. The design-build method (D-B) was chosen for the permanent span replacement with the goal of rapid construction. Three options were investigated: a steel through-truss (a near duplicate of the original span), a steel plate girder span with a concrete deck, and a prestressed concrete girder span with a concrete deck. The steel through-truss, though light in weight and aesthetically consistent with the original bridge, was thought to be too time-consuming to fabricate and erect. The project was advertised for proposal with the assumption that the most- likely structure types for proposal were going to be the steel or concrete girder options. Four D-B teams submitted proposals for the permanent span replacement. Two proposals included the steel girder option and two proposals included the prestressed concrete girder option. WSDOT selected the best-value proposal, which utilized a prestressed lightweight concrete girder deck bulb-tee replacement span. ASPIRE , Winter 2014 | 29 AspireBook_Win14.indb 29 12/10/13 12:54 PM

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