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In the early days of the 20th century, civil engineers were in an arms race to find the best ways to open a bridge.

One novel method was tried out by engineer Ralph Modjeski for Portland’s , completed in 1913. A Rall mechanism employs giant, 8-foot-diameter steel wheels that roll along tracks high above the center of the bridge.

To explain the mechanism’s complex movement to the uninitiated, it helps to have visual aids, said Jon Henrichsen, Multnomah County‘s division manager for bridges.

鈥淚t’s one weird, elliptical motion; it’s much easier to show with pictures, or, better yet, a video,鈥� he said. 鈥淭his is a very complicated bridge 鈥� way more complicated, really, than it needs to be. You can build a simpler bridge that’s easier to maintain and more reliable.鈥�

Like an evolutionary dead end, the was en vogue for only about a decade before simpler, more efficient and economical systems took over. The Chicago-type bascule would become the standard of the style, an example being the Burnside Bridge. But in 2017, the Broadway Bridge and its unique design are still vital to Portland and the 32,000 people who cross the span daily. And now, after a century of rolling back and forth, its .

The four massive wheels have turned more conical than round, and cracks are showing up.

鈥淭here’s just a lot of issues with these,鈥� Henrichsen said. 鈥淚t’s time to replace them.鈥�

The county has contracted with Springfield-based Hamilton Construction to replace the Broadway Bridge’s one-of-a-kind Rall wheels and the tracks and bearings, and rehabilitate the trunnion, control struts and associated structures. It’s a complex undertaking that requires a highly specialized skill set, and it presents its own engineering challenges 鈥� how to lift the bridge to swap out the wheels? How to make them?

To change the wheels, the Hamilton team is lifting the entire bridge, one 1,000-ton leaf at a time. Bridge engineer Ed Wortman likens the problem to jacking up a truck to change its tires, but in this case, no place on the bridge is hard enough to set the 鈥渏ack.鈥�

鈥淚t wasn’t designed to be lifted up into the air as we’re doing now,鈥� Wortman said.

The solution created by OBEC Consulting Engineers of Eugene is a lift system that uses the stone and concrete piers under the bridge for bases, and thick steel plates welded to the bridge. Two 900-ton capacity jacks will work together to push thick posts upward.

This will all go on while bike and vehicle traffic and the Portland Streetcar are moving across the bridge.

鈥淭hey’ll only lift it just enough to get those wheels out,鈥� Wortman said. 鈥淭hen it’s just like changing the tire on a car.鈥�

Wortman was a bridge engineer for Multnomah County starting in the 1990s, but he began working on bridges in 1960. He’s worked part-time since his retirement in 2007, and was on site this month checking progress on the project.

鈥淲e always thought we were going to have to change these wheels, and we thought the designer probably made some accommodation for it,鈥� he said. 鈥淭hen we started looking at it, and it turned out, it wasn’t that easy.鈥�

Ultimately, Wortman said, the decision to use the design was a financial one 鈥� it was slightly cheaper than the other two alternatives. Despite any trouble, it actually has done its job 鈥� creating the widest possible opening for ships 鈥� quite well, he said.

鈥淚t was a complicated system, but clever 鈥� but also, hard to maintain,鈥� he said. 鈥淚t’s pretty special. There’s not another bridge like it in the world.鈥�

Each wheel supports about two million pounds of weight. But those wheels have been rolling back and forth for more than a century. The wheels are solid hunks of steel that start out about 30 to 40 percent larger before being pounded into shape. In 2017, not much metal is forged west of the Mississippi River, but VEGA contracted with Peninsula Iron Works to make the forgings.

The 88,000-pound wheels were forged 鈥� not cast, as were the originals 鈥� at Peninsula Iron Works. The original wheels had cored holes in them like spokes in a bicycle wheel, which helped make them considerably lighter. They were pounded out on the shop’s vertical boring mill, which was manufactured in 1968 but features modern automated CNC controls. They were flipped three times, and shipped on trucks with special permits.

鈥淭his is probably more accurate than they were done historically,鈥� said James Johnson, president of Peninsula Iron Works. 鈥淵our big advantage today would be in how the materials were manufactured, compared to a casting.鈥�

Johnson and his brother are the third generation to operate Peninsula. The fabrication shop performs 3,000 jobs per year. For this one, they were subcontracted under Vigor, which prepared plans and shipped the materials for the forgings. At more than 100 years old and the only shop like it on the West Coast, Peninsula aided the Allied war effort in World War I and mills serving the Pacific Northwest lumber industry. Its handiwork can be found nearly everywhere in the Portland area 鈥� including on all five movable bridges.

Once the new wheels are on, much testing will be needed to ensure they’re aligned with each other and the tracks are oriented perfectly. Among the updates incorporated into the project is breaking up the big metal struts that connect to the control room and pull the bridge open. Breaking them into three pieces, instead of one, makes for easier adjustments.

There will be one, final 48-hour closure over a weekend when final testing will be conducted. Once the old wheels are off, they will likely be shipped to a recycler, though the county has been in talks with the Regional Arts and Culture Council about using one in a public art installation, Henrichsen said.

In Modjeski’s day, bridges had much shorter life spans 鈥� maybe 20 years for the Broadway, Henrichsen said. The original operators of the bridge didn’t even grease its gears.

鈥淗e’d probably think we were crazy to still be operating this bridge,鈥� Henrichsen said of Modjeski.

But a complete bridge replacement project would cost between $300 million and $400 million, and significantly impact commuters.

鈥淎fter all these years, it still works well,鈥� Wortman said. 鈥淪o you can’t question the decision to build it in the first place.鈥�

Broadway Bridge Rall wheel replacement

General contractor: Hamilton Construction

Cost: $13.5 million

Construction start: July

Expected completion: December