Tag Archives | LRT

Checking In on the PMLR Bridge

On Wednesday, I had the opportunity to tour the construction site around the west abutment of the Portland-Milwaukie Light Rail Bridge through the Oregon section of the Institute of Transportation Engineers.

At present, most of the work is centered around the construction of the in-water piers and the two towers that rise from each. The western structure is nearly at full height presently, with the towers rising 160 feet from the pier as seen below (the eastern structure is much smaller at the moment). They’ll be 180 feet when complete.

PMLRTowers.jpg
On the top of the right tower, you can see a saddle structure that was recently installed. The saddles are the parts through which the cables are threaded, and for the bridge to be structurally sound, they must be precisely located with a tolerance of fractions of an inch. To accomplish this, the saddles are placed into steel and re-bar skeletons by “specialists” on the ground and then lifted into place on the tower where the concrete is poured.

PMLRSaddles.jpg

In order to ensure sensitivity to the river’s ecosystem, in-water construction can only take place between July 1 and October 31 each year. So the first structures built last summer were the cofferdams at the base of each tower. I snapped a photo of the underside of the western cofferdam below. The eastern cofferdam is pretty easy to observe from the Eastbank Esplanade. Those views will become much more dramatic as the towers grow.

PMLRCofferdams.jpg

Once the towers are complete, the deck itself will be constructed using the “balanced cantilever” method. The deck will grow outward from each tower structure, always with an equal amount of deck existing on each side of the towers. The cables will be threaded through the deck and towers as the deck grows. The last pieces of the construction will be connecting the two sections of deck in the middle, and then connecting each section to its abutment. The photo below is of the western abutment.

PMLRAbutment.jpg

I snapped this photo from what will eventually become the South Waterfront Greenway, a strip of park with dedicated paths for bicycles and pedestrians. The land around the bridge will see the development of many tall, mixed use buildings like those recently constructed along the south waterfront. The Greenway will, I think, be among the best walks or rides in Portland when our beautiful cable-stayed bridge is finished and the structures begin to rise from its base.