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Temporary Washington I-5 Bridge Replacement Underway
Posted by Tasha Weiss on May 30, 2013 at 4:58 PM.

Workers are already assembling a temporary Interstate 5 bridge span to replace the section that collapsed into the Skagit River near Mt. Vernon in Washington last week, according to an article published yesterday in The Seattle Times.


According to the article, steel plates, girders and truss beams were unloaded in stacks yesterday at the now-unused strip of freeway just north of the bridge, where officials say the first few parts are being fastened together.



The new crossing is being installed by Acrow (an AISC member), a New Jersey-based firm that specializes in the design, manufacture, and supply of modular prefabricated steel bridges. You can see how a temporary bridge is built via an animated video that shows how an Acrow bridge is erected on land, in a manner similar to a big erector set, then launched cantilever-style across the waterway.


Governor Jay Inslee announced the I-5 bridge replacement plan on Sunday: “We will install a temporary span on the bridge that will restore traffic while we build a safe and durable permanent span adjacent to it,” he said. “This plan ensures the economic vitality of Washington state and the communities along this important corridor.”


WSDOT says the temporary four-lane bridge will carry I-5 traffic over the Skagit River at a reduced speed and capacity. The bridge will consist of two, 24-ft-wide structures to replace the collapsed section of the bridge. These structures will be pre-built and trucked to the site to allow for accelerated installation. The remaining southern section has been examined and will not need to be replaced.


WSDOT released a visualization of the temporary replacement bridge.


If the remaining inspections of the bridge structure find no additional damage, the temporary bridge could be in place within weeks. Once debris has been removed, further underwater structural examinations will determine if additional repairs are needed before installing the temporary span.


Crews will immediately start work on the permanent bridge when the temporary span is put in place. They’ll put temporary piers into the river to support a platform adjacent to the collapsed span where the new section will be built. Once complete, the temporary span will be removed and the new permanent span will be moved into place. WSDOT hopes to have the permanent bridge open to traffic in early fall.


According to another article published on Monday in The Seattle Times, the permanent bridge will probably rest upon a half-dozen steel girders, each 160 ft long, that reach from the shore to the first in-water concrete pier.
Harvey Coffman, bridge-preservation engineer for the state Department of Transportation, said steel girders are preferred because they’re lighter than concrete girders, and therefore put less strain on the existing columns, built in 1955.


For additional information on the I-5 bridge replacement plan, see WSDOT’s news release.

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