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Given Jason Kunkle's passion for bridges, he is planted on the perfect professional perch -- high above the Willamette River amid the cross-braced mesh of the Sellwood Bridge's aging steel truss.

In three weeks, Kunkle and a team of engineers, supervisors and skilled workers will culminate months of preparation by activating 10 hydraulic jacks that will lift the 3,400-ton bridge two inches off its concrete piers. In the 12 hours after, they plan to seamlessly pull off one of the longest bridge moves ever attempted.

"If you love bridges, this is what it's all about," said Kunkle, a foreman with

, which formed a joint venture with Sundt, an Arizona contractor, to tackle the $307.5 million replacement of the Sellwood Bridge. "It's a once-in-a-lifetime project."

Challenging facets fill the construction project list. One is the extensive in-water work of sinking long steel columns for both a traffic detour bridge and a work bridge just upstream, which contractors will use as a staging platform to build the permanent structure.

No single aspect of the project, however, rivals the slow-motion drama of the planned Jan. 19 "translation" of the bridge: Stout metal "cradles," lifts and a dizzying system of hydraulics will scoot the bridge deck from its current alignment to the piers that will cradle its temporary incarnation as a detour bridge.

"It's a critical part of the entire operation, and it has taken lots of planning," said Ed Wortman, a retired Multnomah County engineer who was brought back in a temporary, part-time capacity to review work done by other designers and contractors. "Always in the backs of our minds is the thought, what might come up that we haven't thought about?"

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One thing that has warranted plenty of consideration is the age of the steel. When the Sellwood Bridge opened Dec. 15, 1925, it was one of the first large steel bridges in the Portland area that was fabricated on the West Coast.

Some parts of the bridge -- specifically, the steel on the west and east approaches to the main structure -- are even older. They are parts of the original 1894 Burnside Bridge that were recycled into the "new" Sellwood Bridge.

Those pieces, however, will be among the first to go when preparations are made for the bridge move. The east and west approaches will be demolished, with any concrete being pulverized and moved elsewhere and the old steel cut up and carted off for melting down and recycling.

"The steel itself will hold up just fine," Wortman said, "as long as the bridge isn't being bent or rotating. We're taking this long, tricky bridge and keeping it perfectly straight as it moves."

will oversee the move. In doing so, the heavy-lift moving company will use much of the same equipment it employed five years ago to move the arch span for the new Sauvie Island Bridge.

Complicating matters is the planned alignment of the detour bridge relative to the existing span. Although everyone would have loved to deal with a straight downstream push, alignment issues mean the bridge's east end needs to move only 33 feet -- half of the 66 feet the span's west end must travel.

To accomplish the feat, Omega Morgan will control five hydraulic jacks pushing the lifted span, with the west-end jacks pushing twice as fast as their east-end counterparts. Integral to success is a special "digitally controlled power jack" capable of adjusting the amount of hydraulic fluid going to each jack.

U-shaped "track beams," equipped with Teflon pads to provide slick sliding surfaces between the two sets of supports, will guide the truss to its termination point.

The company will also use three methods, including visual and mechanical survey systems, to ensure that the span is moving evenly and without undue strain or deformation to any one spot on the truss.

The county will follow up with two methods of its own, including electrical "strain gage" measurements set up to calculate possible deformations in the steel during the move.

In Wortman's view, the most likely thing that can go wrong is the weather. Too much wind or ice, he said, could delay the move for a day or two.

Otherwise, the move is expected to go smoothly, with the new detour bridge opening Jan. 24 to accommodate the 30,500 cars that use the span daily.

Workers themselves are equally confident of the move's success. Of more concern for many is a bitterly cold work environment that provides no shelter from biting winter winds whipping along the river.

Wet snow and rain that fell on a recent day made things even worse.

"When there's water on the road deck above, it's like a sprinkler system around here," Slayden's Kunkle said. "Just one cold, soggy mess."

A soggy mess, he said with a smile, that he wouldn't trade for anything.

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