Construction of this project was completed in 2002.
Work has been completed on Multnomah County's latest project to rehabilitate the deck of the Burnside Bridge and install a system of seismic restraints. The $2.1 million project was awarded to Mowat Construction Company of Woodinville, WA. Major items of work included replacement of the asphalt wearing surface with microsilica concrete, new expansion joints, new storm water catch basins, a handicap accessible curb ramp at Martin Luther King Jr. Blvd and the installation of seismic restraints.
Traffic lanes on the bridge were reduced from five to four lanes during the project, which was completed as scheduled on November 15, 2002. The work progressed in three phases, with a four-week break for the Rose Festival. Two lanes of traffic were maintained in each direction at most times. Bike lanes on the bridge were removed during the project and bicyclists were directed to use the sidewalks with pedestrians. The contractor used an additional lane of traffic on those evenings when concrete placement was planned.
Seismic Restraints
The Burnside Bridge has been designated as a lifeline structure and evacuation route for the region. To help the bridge withstand the forces of an earthquake, the County completed a Phase I seismic upgrade of the bridge. The retrofit added steel connections between deck spans and at points where the deck meets the main piers and abutments. The Burnside Bridge is the first bridge maintained by the County to receive a seismic retrofit.
Various types of restraint systems were installed at different locations on the underside of the bridge. Each system was designed for the location. At the west Abutment Wall, rod-type restraints with beam seat extensions have been installed to connect the deck stringers to the wall and provide additional bearing surface during a seismic event.
Workers cored through various spots beneath the bridge at Bents 5, 8, 11, 14, 16, 17, 18 and 19 and installed cylindrical-type seismic restraints designed to hold the separate spans of the bridge together during an earthquake. After the hole was cored through, a large threaded pipe was inserted and bolted to the structure, with a nut fitted to complete the installation. Another design using threaded rods was installed on Piers 1 and 4 and Bents 22, 24, 26, 31, 33 and 34.
Stormwater Management
In an effort to reduce the amount of pollutants entering the Willamette River, leaky expansion joint material was removed, and the joints rebuilt and filled with new material. This will allow rain water to flow across joints and into catch basins instead of through them to the structure below.
In addition to this work, catch basins constructed by Stormwater Management Inc. of Portland, were installed at 14 locations to collect rain water, separate trash and large debris and filter the water before releasing it into the city's stormwater system or into the Willamette River. This is the first application of this type of treatment system to a bridge structure.
Deck Rehabilitation
The existing asphalt overlay on the approach structures was removed and replaced with an overlay of microsilica concrete. Roto-milling machines were used to remove the asphalt layer. Shot Blasting machines followed to clean up the surface and provide the proper surface profile for the concrete to adhere to and bond with the deck. Bid-well machines were used to uniformly distribute the concrete across the deck and eliminate the need for extensive hand-finishing. The new concrete was placed at night when traffic impacts and vibrations were at their minimum. Similar work was completed by the County on the Morrison Bridge's east ramps in 2001. The microsilica concrete overlay will last longer than asphalt and provide additional strength to the existing bridge deck.
Handicap-Accessible Sidewalk Ramp
In addition to the other features of work, the County, in conjunction with the City of Portland, has constructed a handicap-accessible ramp at the SW corner of East Burnside and Martin Luther King, Jr. Blvd. Due to the unique sidewalk construction at this corner, the sidewalk was widened an additional 5 feet to allow for the construction of ramps. There is no change to the original crosswalk layout at the intersection or to traffic lanes existing the bridge.