Morrison Bridge Update

Morrison Bridge Update
Posted by on August 17, 2017
Posted in: built projects, construction, events, legal, transportation
Last night I walked down two flights of stairs into “the pit” of the Morrison Bridge. As part of a tour organized by WTS Portland, I got to see the current state of construction first hand, including the counterweight mechanism below the bridge.
It’s not the first time I’ve been “down below”. Back in 2014, Fat Pencil Studio assisted Multnomah County in litigation related to the defective installation of a fiber reinforced plastic (FRP) bridge deck. Three years later, they are nearing completion of a new deck comprised of steel and lightweight concrete. The Eastern lift span deck is mostly complete, though the concrete is a bit rough pending installation of a thin driving surface to match the surrounding roadway. On the Western lift span, open steel mesh is awaiting a concrete pour. The last remaining FRP panels can be seen on the South side, with bolts and glue holding them in place.
The roadway surface in different states of completion

The bridge lift operator works from here

View toward Mt Hood from operator booth

The new concrete and steel bridge deck is more than twice as heavy as the open steel grate or FRP system that was installed previously. As a result, major changes had to be made to the counterweight and lift mechanism. Hundreds of steel plates were hung off the back of the already massive counterweight, and thousands of concrete blocks were carried inside by hand. The entire lift span is balanced on a trunnion pin, which also had to be bulked up to carry the added load.
close-up view of trunnion pin

The counterweight (right side of image) sits inside a giant pit

Concrete blocks stashed inside the counterweight

Steel plates hang on back of counterweight

All this engineering gets a live test this weekend when the new East span opens for the first time. If all goes according to plan, prime contractor Hamilton Construction will move ahead with pouring the West side deck in the coming weeks, and be on track to open the full bridge toward the end of October.

About Joshua

Joshua Cohen founded Fat Pencil Studio in 2004. Read more