Installing new steel grate deck on Morrison Bridge lift span. It will be filled with concrete this summer.

The failing deck of the Morrison Bridge lift span will be replaced with a solid new deck in 2017. The work will require major traffic changes starting April 3 as the old deck is removed and the new one is installed.

Project Facts

  • Preliminary work began in March 2017, with minimal impact on bridge users. The contractor added weights to the counterweights under the bridge deck, to balance the heavier weight of the new lift span deck. 
  • Four of the six traffic lanes will be closed from April 3 through October. One lane will be open in each direction. The westbound lane is only open for traffic exiting I-5 and I-84.
  • Westbound traffic from the Central Eastside can use the ramp to access I-5 north, but will need to use a different bridge (such as the Burnside or Hawthorne) to reach downtown.
  • Traffic is currently shifted to the north side of the bridge and the north sidewalk is open to pedestrians only. The south multi-use path is closed for several weeks starting September 8. Bicyclists and people who use a mobility device should use alternate bridges such as the Hawthorne and Burnside. 
  • The bridge was closed to traffic for two weeks in July and August to pour concrete for the east leaf deck. A two-week closure begins in mid-September for the west leaf deck pour.  The tentative closure dates are September 25 to October 8.
  • The deck will replace one that deteriorated prematurely after installation in 2011 - 2012.  
  • Total project cost for the design and construction phases is $10.4 million. 90% of the funds are federal, 10% county.
  • Hamilton Construction was awarded a $6.5 million contract to install the new deck in 2017.
  • The temporary vehicle weight limit of 10 tons on the bridge and the temporary speed limit of 25 miles per hour will be removed after the new deck is installed in fall 2017.  

Lane closures during north work zone phase.
Lane closures during north work zone phase.

Lane closures during north work zone phase.
Lane closures during north work zone phase.

Cross section showing traffic plan during work on north side of bridge.
Traffic Impacts

Construction work in March 2017 focused on strengthening the lift span, which did not impact traffic.  Work to replace the lift span deck will close four traffic lanes from April 3 through October 2017. A single lane is open in each direction over the river, but the westbound lane is only for traffic exiting I-5 and I-84. Several night-time bridge closures are planned this spring but two-way traffic will be maintained on the bridge at other times.  Westbound access from the eastside will be limited to Interstate  5 north access only.  Westbound bridge users will need to use a different bridge from the inner eastside, such as the Hawthorne or Burnside. 

The following traffic configuration is in place:

  • Two traffic lanes are open on the north side of the bridge.  
  • The north sidewalk is open to pedestrians.  The south multi-use path is closed.

The bridge will need to close to all vehicle traffic when concrete is poured for the east and west leaves of the lift span. Full bridge closures lasting two weeks are planned to begin in mid-July  and in mid-September.  The closures are needed while the concrete is poured and cures, to avoid cracking the concrete from traffic vibrations.

Until the project is complete in October, only one of the two drawbridge leaves can open for river traffic. 

The gross vehicle weight limit on the bridge was reduced from the 40 tons (80,000 pounds) to 10 tons (20,000 pounds) in April 2015.  Bridge speed limits were reduced from 35 to 25 miles per hour. The measures were implemented to extend the life of the FRP deck until it is replaced.  The weight and speed limits will be increased in fall 2017 after the new deck is installed.

TriMet's #15-Belmont/NW 23rd line is temporarily re-routed to the Hawthorne Bridge due to the reduced weight limits. For information on the re-route, visit TriMet's webpage for the #15 Belmont/NW 23 line.

Project Overview

The solid deck installed on the bridge in 2011 was made of fiber reinforced polymer (FRP). It replaced an open steel grating deck that had lasted 50 years, but provided less traction for vehicles in wet weather.  Choices for the lift span deck type are limited because the deck’s weight needs to be balanced by the weight of two 1.9 million pound concrete counterweights, and supported by the bridge structure.

After the deck began to fail soon after installed, County engineers and consulting engineers from David Evans and Associates investigated replacement deck options with consultants and state and federal agency staff. The process led to the selection of an open steel grating deck that will be filled with a top layer of lightweight concrete.  The concrete layer is two inches thick and has a top layer of a polymer asphalt for improved vehicle traction compared to the original deck. This deck type has a long history of use on bascule drawbridges like the Morrison.

The open grating concrete filled deck was not chosen in 2011 primarily due to its heavier weight. The new deck will weigh 44 to 47 pounds per square foot, compared to 20 pounds for the original open steel grating deck and the FRP deck. Analysis in the last year has confirmed that the bridge structure can support the additional weight.  The weight of the two counterweights will be modified to support the extra weight of the new deck.

The Morrison’s original lift span deck was an open steel grating that had degraded after 53 years of use.  The old deck was replaced with one made of FRP panels similar to decking installed on the county’s Broadway Bridge in 2010.  The Morrison Bridge FRP deck began to show signs of failure in 2012, and an in-depth investigation confirmed that many panels were loosening and deteriorating.  The FRP deck was the subject of litigation that has been completed. County staff regularly monitor and repair the deck to ensure the safety of the bridge for vehicle traffic. 

Multnomah County maintains the Morrison Bridge, five other Willamette River bridges, and 300 miles of roads. For information, visit www.multco.us/bridges.