Workers already are assembling a temporary Interstate 5 bridge span to replace the section that fell into the Skagit River last week.
Steel plates, girders and truss beams were unloaded in stacks Wednesday at the now-unused strip of freeway just north of the bridge, where officials say the first few parts are being fastened together.
“They’ve been rolling in,” said Kris Olsen, spokeswoman for the state Department of Transportation. “We should have the last loads in the morning.”
The new crossing, to carry traffic by mid-June, is being installed by Acrow, a New Jersey firm that shipped about 10 truckloads of parts from Camas, Clark County.
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In September, the state DOT expects to finish a permanent, four-lane roadway, supported by giant steel girders from beneath. Total costs are expected to be about $15 million, the department says.
Acrow’s bridges resemble military-style “Bailey bridges” that were deployed in World War II. They are made of 10-foot-long beams fastened in sequence, said Chief Executive Bill Killeen.
The company provided 18 bridges on the south and east sides of Mount St. Helens after the volcano erupted in 1980, he said.
The Skagit job requires a pair of narrow two-lane decks, each 160 feet long. That size, “is well within the range of structural capability” Killeen said. Many years ago, Acrow built a 300-foot bridge over the Klamath River in California, he said.
The steel is U.S.-made and fabricated near Williamsport, Pa., said Killeen. Much of the Skagit supply is new, and some reused from a bridge in Hawaii, he said.
Meanwhile, the retrieval of broken truss beams continues in the river, where some parts of interest to the National Transportation Safety Board remain submerged.
After those are carefully removed, state contractor Atkinson Construction can quickly extract the other beams and the deck. The concrete roadway “slid off its girders like frosting off a cake,” after Thursday night’s crash, NTSB Chairwoman Deborah Hersman said last weekend.
The collapse was triggered when an overheight load, going south toward Vancouver, Wash., struck about 10 crossbeams. One or more hits caused the northernmost of four bridge spans, built in 1955, to fall in a second or less.
The cargo, known as a casing shed, was part of a drilling platform. This kind of piece wasn’t commonly carried across the bridge, said Ed Scherbinski, vice president of Alberta-based Mullen Trucking.
It was one of two loads Thursday night destined for a storage yard, he said.
“We’ve taken bigger pieces than those,” he said. “We specialize in over-dimension, heavy equipment.”
The platform is used for conventional oil drilling and could be used for wells and mining, Scherbinski said.
The load was registered as 15 feet 9 inches in a state permit, while the bridge clearance is 15 feet 6 inches at the edge of the right lane, and 14 feet 6 inches near the right guardrail — so the truck needed to be in the left lane.
Security video footage shows a white truck passing the tall load near the bridge entrance.
The sequence raises a question, being explored by NTSB, about whether driver William Scott was hindered from moving left.
There was no pilot car required in the rear to block any passing.
“We are reviewing the videos and probably will do so again back in our lab here in D.C. This will help us corroborate what we are seeing in evidence, with what the video shows. Right now, we are not in a position to rule anything out,” said NTSB spokeswoman Kelly Nantel.
Mike Lindblom: 206-515-5631 or firstname.lastname@example.org.
On Twitter @mikelindblom