Construction of this project was completed in 2007.
A two-year construction project on the Burnside Bridge has completed its final stage. The $9 million project completed critical repairs to the lift span of the historic bridge. Repairs included replacement of the lift span deck and replacement or repair of parts that help open the bridge which opened in 1926.
Mechanical repairs to the bridge were completed during a bridge closure that ran from September 17 until October 17, 2007. During that time the contractor replaced or repaired parts that help open the bridge. An original hinge that attaches the 3.8 million pound counterweight to the lift span was broken and would not turn freely. Stress from the frozen hinge caused the eastern leaf of the bridge to open slower than the western leaf. If the hinge were to fail, the east leaf span would have been able to open.
Replacement of the pin and bearing that form the hinge was technically challenging. The contractor had to detach the counterweight and lower it to replace the parts. A complex rigging system supported the counterweight while it is detached. The repair may be the first of its kind, due to the Burnside’s rare design.
The four-week bridge closure was needed to ensure the safety of the public, workers and the bridge itself. Vibrations from traffic could have impacted drilling operations and other work. The repair required the contractor to assemble parts that have very tight tolerances.
About 45,000 vehicles cross the Burnside Bridge on a typical day.
The project made these improvements to the bridge:
• Replaced lift span deck and sidewalks
• Installed seismic restrainers
• Installed new motors and brakes and repaired gears
• Replaced electrical wiring
• Installed storm water collection and treatment facilities, and
• Replaced or repaired corroded steel.
The concrete deck of the lift span was worn from eight decades of use and was completely rebuilt. The Burnside Bridge has one of the largest concrete decks of any bascule drawbridge in the world. At less than five inches thick, the deck is also extremely thin for a concrete deck that is stressed and flexed by regular openings.
Rebuilding the deck while keeping the bridge open to road and river traffic is one reason construction took two years. The contractor had to keep one leaf of the lift span operable so the bridge could open for river vessels.
In order to keep the bridge open to road and river traffic, the new deck was built in four stages (two per lift span leaf). Each stage required one month of curing time before the new concrete was strong enough to handle the stress of traffic and bridge openings.
While the project inconvenienced bridge users, it extended the life of the historic bridge, which opened in 1926.
Federal funds covered 70% of the $9 million project, while Multnomah County contributed the rest.
Multnomah County maintains the Burnside Bridge, five other Willamette River bridges and 300 miles of roads.