MOUNT VERNON — The work to put a permanent replacement span on the I-5 Skagit River bridge that collapsed in May is at a crucial stage, the state Transportation Department said.
Eight girders — each one 162 feet long and weighing 84 tons — are being moved into place next to the temporary span, spokesman Dave Chesson said Wednesday. Three were delivered Tuesday, three more were arriving Wednesday and the last two will arrive today.
Moving each steel and cast concrete girder into place is a tricky maneuver that requires coordination among two cranes — one on a floating platform in the Skagit River — and the truck that hauled it from Tacoma on a rig so long it requires a separate steering mechanism on the back for sharp turns.
Overall, the work is on track to slide the permanent replacement into place after Labor Day, Chesson said.
“This is really a major milestone,” he said.
Repairs have been underway since an oversize truck load hit the bridge on May 23, sending one 160-foot section and two vehicles with three people into the water. No one was killed.
Traffic was detoured for a month through Mount Vernon and Burlington until a temporary span was installed. The Max J. Kuney Co. of Spokane has a $7 million contract for the permanent span, which carries about 71,000 vehicles a day, the Transportation Department said.
Replacing a bridge with the least disruption to traffic is an engineering challenge. It involves building platforms over the water on either side of the bridge. The temporary span will slide off onto one platform. The permanent span will slide from the other platform onto the existing piers, Chesson said.
In addition, moving the huge girders in tight quarters requires a ballet of coordinated movements. A crane on the river dike lifts one end of the girder off the slowly backing truck. The crane hands that end off to the second crane floating in the river and picks up the other end from the truck. Then the two cranes put the girder on the platform.
“It was quite an operation,” he said of the first day’s work. “It’s amazing. A lot of engineering expertise went into every single aspect of doing this.”
The temporary span should be rolled off and the permanent span rolled on before October.
“So far, so good,” Chesson said. “We’re on schedule.”
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