Readying a Vulnerable Region for Recovery

• Comprehensive services from bridge engineering to public involvement
• Seismic resiliency for a critical lifeline bridge
• Consideration of more than 120 bridge options and selection of the preferred type
• Bridge design that integrates a bascule movable span, a cable-stayed structure, and long-span steel girders 

The Burnside Bridge in Portland, Oregon, straddles the Willamette River in one of the world’s most powerful earthquake zones. HDR has assisted Multnomah County with a wide variety of engineering and environmental services tied to improving the crossing. The ultimate goal is to replace the existing structure with a new, more seismically resilient crossing. 

Developing Resilient Bridge Alternatives

Oregon sits in the Cascadia Subduction Zone, making it subject to some of the world’s largest earthquakes. Since being identified in the 1980s as an active fault line immediately off Oregon’s coast, scientists have documented a long history of earthquakes and tsunamis in the zone, regularly causing catastrophic damage in the region. 

In a major earthquake, Portland’s downtown bridges are all expected to suffer moderate to significant damage. If not collapsed, all are expected to be at least rendered unusable, threatening critical emergency response, evacuation, and recovery efforts.

To help address that threat, Burnside Street and the associated Burnside Bridge, built in 1926, were identified as a critical “lifeline route” that should be able to withstand the next earthquake and either remain open or reopen quickly after a major earthquake event. 

Our services included identifying the existing bridge’s vulnerabilities; public involvement and stakeholder outreach; exploration of funding options; structural engineering (including bridge, seismic, geotechnical, and hydraulic engineering) movable bridge engineering (mechanical, electrical, and seismic); civil engineering (including traffic, roadway, site civil, surveying, urban design, and landscape architecture); and geo-environmental and cultural resources. 

High-Tech Public Outreach

An important part of our public outreach was helping Multnomah County build support through a public outreach campaign that drove home the need for action. Animators based in our Boise, Idaho, office created a true-to-life video of how the bridge would shake, sway and eventually crumble onto nearby interstates and into the water during a major earthquake. 

The video, a vivid illustration of the need for the project, was released publicly in 2017 and quickly received coverage in local media. Since its release, the animation has been seen in nearly 100 countries and received more than 80,000 views. 

Bridge Design Expertise at Work

Beginning in 2016, our team conducted a feasibility study of the bridge’s seismic vulnerabilities that considered more than 120 bridge options, eventually identifying four alternatives (three replacement and one retrofit) for further evaluation in the Environmental (NEPA) phase beginning in 2019. In the process, a set of unique seismic design criteria was developed in conjunction with leading industry experts. Input was also solicited from the community and regulatory bodies. At the end of this phase, a replacement long-span bridge was chosen as the preferred alternative. 

Concurrent to the earthquake resiliency study, we also led the design of rehabilitation work on the current, aging bridge. Our bridge engineering experts provided structural, mechanical/electrical, and roadway rehabilitation improvements to address safety issues on the current bridge, as well as its load-carrying capacity and reliability, to extend the Burnside Bridge’s service life until its planned replacement by 2035.

In 2024, after further design work and community input, it was determined that the new bridge will have long, steel girder-style spans on its west approach, a bascule-style movable span over the middle of the Willamette River and an inverted Y-shaped cable-stayed design on its east approach. Similar to the other downtown vehicular bridges, a movable bridge type was maintained over the Willamette River to make sure that ship vessels, which can reach up to 160 feet above the water surface, can cross without the need for a much taller, longer and more expensive bridge to provide the same vertical clearance. Our team is advancing design of the bridge toward the 60% final design milestone.  

The new Burnside Bridge will have two vehicular lanes in each direction, with one eastbound lane dedicated to buses, similar to current conditions. Bike and pedestrian paths will create a safer active transportation experience on both sides of the bridge, each being 17 feet wide and protected with barriers. The new Burnside Bridge will have the widest bike and pedestrian space of any downtown Portland bridge.