On May 23, 2013, a semitrailer carrying an oversized load struck a steel truss bridge over the Skagit River on Interstate 5 in Burlington/Mount Vernon, Wash. The crash caused a 160 ft (49 m) long section of the bridge to collapse in seconds, severing a primary North American trade and transportation corridor. To get traffic restored and commerce moving again, two temporary bridges were installed, but the state needed a permanent solution.
To get a new span open as soon as possible, Washington State Department of Transportation (WSDOT) chose a precast concrete design and design-build delivery, ensuring quick, safe, and cost-effective construction that minimized the need to close the interstate.
"The use of precast girders provided schedule certainty, which was critical to our proposal to WSDOT to open the new permanent span in less than 90 days," says Max Kuney, president of Max J. Kuney Co., the contractor on the project. "We analyzed using steel girders for the span; however, we were not 100% convinced that we could procure and fabricate the steel in the time required. Concrete Technology [the precaster on the project] and precast girders gave us that 100% certainty."
To meet the project constraints, including the aggressive schedule, vertical clearance requirements, and span weight limitations, an integral concrete deck girder system was enhanced with the introduction of an innovative full flexural-shear connection. The project also used the state's first lightweight concrete in the girders and diaphragms. "The lightweight concrete girders were key to being able meet the span weight requirements of 915 tons," Kuney says.
To meet the schedule, special aggregate for the lightweight concrete girders had to ship just two days after the notice to proceed was received from WSDOT. To speed the process, the release for construction drawings was submitted simultaneously with the shop drawings from Concrete Technology.
The superstructure was then constructed on a parallel temporary steel support structure while maintaining all lanes of traffic on the interstate. Once completed, the temporary steel bridge structure was removed and the 1.8 million lb (80,000 kN) permanent concrete deck girder system was placed under a full overnight closure using a skidding system on rails located 20 ft (6 m) from the beam ends.
Thanks to collaboration among all of the project teams and the efficiency of the precast concrete solution, the project was completed ahead of the client's original schedule, Kuney says. "The bridge opened to the public on September 15, 2013, following a single 19-hour closure of the interstate, 115 days from the initial accident and 88 days from the team's notice to proceed."
In addition to restoring a vital transportation and trade corridor, the project resulted in four successful and significant first achievements for the owner. It was the first emergency design-build contract using federal funds, the first decked bulb tee girder bridge design on an interstate highway in the state, the first use of an innovative full-strength closure between girders, and the first use of lightweight aggregate by the owner.
"The Skagit River Bridge project was a very successful one from the standpoint of our client, WSDOT," Kuney says. "Both the public and media outlets were impressed over the high quality and speedy completion of the project."