Our transit agency has an extensive network of light rail tracks that's ever expanding. Their current project includes building a new bridge across the Willamette River in downtown Portland. As one of the local agency review engineers, I had a small role in the preliminary design phase of this bridge. Now that construction is underway, I sometimes get opportunities to tour the construction site. Is there anything cooler than watching a bridge being built? (Especially to a nerdy civil engineer!)
|Towers rising out of the river|
Construction started in the summer of 2011. To build the bridge piers, giant cofferdams were placed in the river, the water pumped out, and huge shafts drilled into the river bottom. Filled with concrete, these became the foundations. Then, throughout the year, two towers slowly rose out of the water.
These photos are from September 2012. The tower near the west shore was nearly 2/3 complete.
A close up of the west tower. Look at the long staircase workers must climb to reach the top!
|Concrete pour from the workbridge|
For access from shore, a sturdy workbridge was built. This enables delivery of construction materials to the work area and easy access for the workers. Concrete trucks can drive very close to the towers. The long green arm is a pump that gets the concrete up to the work platform. As you can imagine, it takes a lot of concrete to build a bridge of this size.
|Towers on the east shore|
A look at the east tower. Not very far along at this point. The green rectangles you see are rebar cages that form the skeleton of the towers. Forms will be placed around the rebar and the cage will be filled with concrete. As you can see, there's a workbridge on this side of the river too. Cranes balanced on huge barges do the heavy lifting.
|We engineers love this stuff!|
Some facts: This will be a cable-stayed suspension bridge. When completed, the bridge will serve light rail trains, streetcar, buses, pedestrians and bicycles, but no private autos will be allowed. It will be approximately 1,720 feet in length, and the towers will each be 180 feet high. It's the first new bridge built across the Willamette River in nearly 40 years.
|A year later.....|
Fast forward to November 2013. Not only are both towers at full height, but the concrete bridge decks, anchored by long cables, extend from both sides of each tower. The abutments on both shores are well under construction, and the bridge decks are getting ever closer to reaching land.
|Form traveler on the west end|
Last week, I got another opportunity to visit the construction site. Not only that, I was able to go up on the bridge itself! Not many people are allowed to get so close.
This shot is two photos stitched together. It shows the form traveler on the west end of the deck. The deck is built outward in both directions from the towers, keeping each side in balance. The form traveler moves with the extension of the deck. As construction progresses, cables are cast into the deck's underside.
|Underside of the west tower|
I think this is an interesting view of the bridge's underside. A lot sure has happened in a year!
|The decks are getting closer...|
Eventually the deck will touch the abutments on each side of the river. And the other ends will meet in the middle of the river. In this photo, it looks as though the decks are getting close to touching, but I'm told this closure won't happen until next May.
|Soon they will meet!|
Here's a view of the deck's underside, suspended over the river. I think it's so amazing that a bunch of steel cables can hold up so much concrete!
|I see the cables up close and personal|
This is my view from the bridge deck. Is this awesome or what? Each of these white pipes house over thirty individual steel cables. The cables run through a hole in the tower, and are cast into the bottom of the deck on both sides.
|View from center span|
Walking in the middle of the deck, where the future tracks will be laid, gives you an idea of the huge scale of such a structure. Tracks will be located in the center of the bridge, and each outer side will have a wide path for bikes and pedestrians. In the future, it will be great to walk across this bridge and take in the city and river views. Someplace to bring my camera, that's for sure!
|Cables radiating out from the tower|
It's fun to see a project move from words in meetings, to lines on a plan sheet, to an actual steel and concrete structure. Scheduled for completion in late 2014, I can't wait to tour the finished product.
For more information, check out the transit agency's website.
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