Freewheeling at the Broadway Bridge
Lanes on the Broadway Bridge have been shut down over the past few months so contractors could attach jacks to its supports and replace four Rall wheels and their tracks.
All of the parts are 104 years old and have never been replaced. The Broadway Bridge's Rall wheels are the largest still operating in existence, each with an eight-foot diameter.
The Broadway Bridge is a bascule bridge, which lifts up by rotating about an axle. It has four Rall wheels that pull it up and out, named after Theodore Rall, who patented the idea. Ralph Modjesky was the original designer and engineer of the Broadway Bridge, ocompleted in 1913.
Brett Schneider, engineering and construction consultant with Schneider Consulting, LLC is the project manager on the bridge's wheel- replacement project.
"This bridge is unique in that it opens up, it has these wheels that pull the bridge backward — it's going two directions at one time, opening up and rolling back," Schneider said. "(The Broadway Bridge) is the largest of its kind in the world."
The Rall wheel style of bridge engineering was only popular for a short time, according to Jon Henrichsen, the head of county bridge services with Multnomah County.
"Around this time (1913, when the Broadway Bridge was originally built), there were competing bridge designs for a brief period of a few years, and this Rall wheel design caught on, but it was very short," Henrichsen said. "We have one of the largest in the world, and it's definitely the largest one still operating — there are maybe only two others in the world still operating, and they're tiny by comparison."
The Hannover Bridge in Connecticut has Rall wheels with a four-foot diameter. Another one in Pennsylvania has two-foot diameter wheels, and there's one in Chicago that doesn't operate anymore.
"To those of us in Portland who drive across, it looks like an old red steel bridge," said Mike Pullen, communications coordinator with Multnomah County. "The stuff up above where you drive is very unique in the world, a real challenge and parts wear out — there are very few examples in the world you can copy. This is the only time these wheels will be replaced: most of them (this type of bridge) never got that old that they had to have wheels replaced."
To bring this project together, the county started studies on the bridge in 2010, and discovered the wheel and some small cracking problems in 2012. It was at the same time the new Sellwood Bridge was under construction. The Broadway Bridge uses the CM/GC, or construction manager/general contractor, a project delivery method of collaborating with contractors during the design phase, the same as the Sellwood Bridge.
"From a tech standpoint, the largest (challenge) we've run into that we didn't know about beforehand was one of the wheels was misaligned with the track runs, and we think that was built that way, or has been that way for many years," Schneider said. "When we pulled the old wheel out, we were able to confirm that the (pieces) that hold the axle into the wheel were pointing the wrong direction, and used a line boring machine to realign the wheel. That was a bit of a stress fest the past few weeks."
The whole bridge has been pulling north, especially when the left wing was open. Schneider called it "almost an emergency repair."
The Rall wheel replacement project has never been done to this scale before, and the engineer had to do the math with theoretical numbers: ultimately to jack the bridge up 1/8 of an inch — because the jack gets squished as it pushes up, and the steel supports lengthen with relief — they really had to jack it up 5/8 of an inch.
"Each leaf rolls back as it opens on two wheels," Henrichsen said. "The wheel on the south side was oriented so the axle it rotated on was perpendicular to the tracks it rolls on. On the north side, the wheel was pointed a little to the north — not a lot, but enough so that every time the bridge opened, it wanted to drive the bridge in the direction of north instead of going east-west."
They replaced the axle wheel, the trunnion in the bridge's peak, the tracks the wheels ride on and all the components of the Rall wheels on all four corners of the bridge, which had all original parts.
"The misalignment broke the track on that north side, which caused some of the problems," Henrichsen said. "The wheels themselves were rolling back and forth for 100 years, and the surface started to get small cracks all over it, so we were concerned at some point that would develop into larger cracks that would cause something to break so that we could not fix the bridge at all."
And because the river was there before the bridge, the river traffic has priority over the surface traffic.
"Worst case scenario, it could be a broken drawbridge that has to stay up (forever) because it can't block river traffic," Schneider said.
Jacking up the bridge
The major construction work started in August, and the site usually has between 10 and 12 laborers working on it at a time.
Changing out the Rall wheels is similar to changing a very heavy flat tire.
"The way we've changed the wheels out is literally by jacking the bridge up," Henrichsen said. "We basically use the part of the bridge where the concrete goes into the river — that's one of the reasons why two lanes are closed — the jacking system goes through the part you normally drive on and touches down five to 10 feet below. The traffic jack on top of that concrete pier goes deep under the river. That's what they use for the ground, to lift off from."
Each leaf being jacked up weighs over 2 million pounds; they used a 4100W Manitowoc Crane.
Adding to the complexity is the streetcar wire that runs across the Broadway Bridge: every time the team needed to do work, streetcar electricians had to come out and adjust the wires.
"The system that gets the power for the electrical lines from the part of the bridge that doesn't move, to the part of the bridge that does move, was in the way of us doing this work, so the streetcar had to take all those electrical connections out and make direct electrical connections between parts of the overhead wiring system that normally moves out of the way when the bridge opens. That means every time we want to work on the bridge right now, the streetcar has to come out and do an hour's worth of work to make it so we can open it," Henrichsen said. "That's been tough for us and for the streetcar because often we want them to do that work at 3 a.m. so we don't interrupt people driving home from work."
Manufacturing the new Rall wheels
The new wheels and tracks are designed by New York-based Hardesty & Hanover infrastructure engineering firm, which specializes in moveable bridge engineering and working on old bridges across the country.
Subconsultant OBEC from Eugene designed the system to lift the bridge up in the air.
"They designed the new wheels and tracks to be a little different than the old ones," Henrichsen said. "The new ones are giant, they're heated up until they're really hot and beaten down into shape, which makes it much stronger than regular steel."
The County recognized some issues with the old ones, and ordered these to be made stronger.
"We decided to make these (new) wheels solid to save the effort of making big blocks of steel, beating them into shape and cutting out all the parts to make them look like the old wheels,' Henrichsen said. "That meant we had to get 10-foot-diameter steel, heat them up, beat them down ... and you can only get that done a few places in the Midwest."
North American Forge Masters in Ohio did them.
"When they arrived in Portland, they were big, round discs," Henrichsen said. "Then they machined holes into the center — they did that cutting here — inserted the bushing (metal lining that protects electrical cable) here for the trunnions and shafts to ride on, then cut into the side of the wheel to give the appearance of the old wheels they're replacing."
The old wheels weren't solid steel: they were three castings welded together to create one big wheel with an 8-foot diameter and 3.4 feet wide. They had spokes instead of being solid, and weighed about 56,000 pounds each. The new wheels are closer to 90,000 pounds — and are solid.
"Every neighborhood group said what's going to happen to the old wheels," Pullen said. "We're saving two wheels and two tracks: we hope to find a place near the Broadway Bridge, maybe on private property, maybe a future apartment building or condo tower's courtyard, and we're willing to donate a track and wheel. The other set we want to give to a university to dissect and let engineering students learn how they did stuff 100 years ago."
By Jules Rogers
Reporter, The Business Tribune
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Total budget: $13.5 million
Owner: Multnomah County
Contractor: Hamilton Construction
Designer: Hardesty & Hanover
Engineering subconsultant: OBEC Consulting Engineers
Final machine fabrication: Vigor
Jacking system steel fabrication: Peninsula Ironworks