New Sellwood Bridge will be built to withstand a major earthquake

Recent world events remind us how important it is to build structures so they can survive a major earthquake. The new Sellwood Bridge is being designed to the latest seismic standards. Bridge designers will take into account all the potential seismic conditions in the region and at the site of the new bridge.


The 1989 Loma Prieta earthquake caused an upper deck section of the San Francisco-Oakland Bay Bridge to collapse onto the lower deck.

All the existing Willamette River bridges in Portland were built before local seismic risks were well understood. Two existing bridges (the Burnside and Marquam) have had seismic upgrades in recent decades. But no upgrade can match the built-in strength of a new bridge designed to today's seismic standards.

Engineers do not design bridges to survive a specific Richter level, a number that only describes the motions at the actual spot where the rupture occurs. Instead, bridge designers use seismic history based on the frequency and intensity of earthquakes felt at each specific site. The methodology is similar to designing for flood events. The new Sellwood Bridge will be designed to address both 500 and 1000-year recurrence period earthquakes. The seismic goal is for the new Sellwood Bridge to remain standing through an earthquake that is equal to the largest felt here in the last 1000 years.

The 500-year standard is for a smaller earthquake. In that case, the bridge would not only remain standing after the earthquake but would need only moderate repairs after the event.

Bottom line: The new Sellwood Bridge (and the new TriMet light rail bridge) will be built to today's seismic codes and will be the local Willamette River bridges best designed to survive a major earthquake.

Read this technical memo for more information about seismic design for bridges.

Arizona bridge comparison helps explain Sellwood Bridge cost

Comparing costs: A tale of two bridges

When comparing the cost of two items, a shopper needs to know what’s included in the price. The author of a recent letter to a community newspaper wondered why the new Sellwood Bridge has a higher cost than the recently completed Mike O'Callaghan-Pat Tillman Memorial Bridge in Arizona (shown in photo below).


Mike O'Callaghan-Pat Tillman Memorial Bridge Rendering in Arizona
The Arizona bridge is in an iconic location, spanning a steep canyon near the Hoover Dam. The citizen assumed it should cost less to replace the Sellwood Bridge. He encouraged Multnomah County to hire the firm that designed the Arizona bridge to help lower the Sellwood Bridge cost.


Sellwood Bridge Rendering
When the letter was published, the Sellwood Bridge Project had a cost of $330 million and the final cost of the Arizona bridge was roughly $116 million. The cost of the Sellwood project has since been reduced to $290 million, after the County approved a redesigned Westside interchange and refined the cost estimate. That’s still a big price gap between the two projects.

The letter caused Multnomah County staff to do a bit of research to compare costs of the two projects. What we learned helps explain the cost of the most expensive transportation project in our county’s history.

• Cost Elements: The key difference in the price of the two bridges is that the cost of the Arizona bridge is for the bridge only while the Sellwood estimate includes all project costs. These include a westside intersection with Highway 43 that is still expected to cost roughly $80 million. Other items in the Sellwood estimate include right of way (land and structures), design, and costs to protect the environment. The current cost estimate for just the bridge portion of the Sellwood project is roughly $164 million.


• Year of Estimate: The Arizona bridge costs are from a bid in 2004. The Sellwood Bridge estimates are for 2014, the projected middle year of construction. Costs have risen significantly in the past decade due to inflation which averaged 3 – 4% a year during the decade. Inflation accounts for a cost increase of 40 – 50% over 10 years.


• Geology: The Arizona bridge was built into the solid rock sides of a canyon, so deep foundations were not needed. The river and land piers supporting the new Sellwood Bridge will require deep foundations to support the bridge in river sediment and in a landslide zone on the west side.


• Right of Way: The Arizona bridge was sited on federal land so there was no right of way (property) to buy. The Sellwood Bridge is surrounded by private property, especially on the east side. About $36 million will be spent for Sellwood right of way.


• Construction/Traffic Staging: Because no one lives near the Hoover Dam, construction can happen seven days a week, around the clock. Even with construction easements, the close proximity of residential buildings to the Sellwood Bridge constrains a contractor’s work. Work hours and days will be restricted for the Sellwood construction. Also, the Hoover Dam bridge was in a clear, open site with no existing bridge traffic to keep flowing. The new Sellwood Bridge will be built while maintaining traffic (30,000 vehicles a day) throughout construction. This adds complexity, time and cost.


• Environmental: Due to the presence of protected fish species in the Willamette River, construction of the Sellwood Bridge in-water work will be limited to four months each year, while the Hoover bridge was not. “In-water” work is construction that impacts river sediments, such as pile driving or digging for columns. This adds more complexity, time and cost.


• Demolition: The Sellwood cost includes removal of an old bridge, while the Arizona bridge did not.


• Designer: The letter author suggested Multnomah County contact the designer of the Arizona bridge to give us advice on how to economize our project. We have. The County hired the same bridge engineering firm (T.Y. Lin International) and the same Chief Bridge Engineer (David Goodyear) who designed the Arizona bridge. David is one of the premier bridge designers in the U.S. and we are thrilled to have David and his firm leading the Sellwood design team.

Taking all this into account, it’s clear the costs quoted for the two bridges are not apples to apples. However, all parties agree that the cost of the new Sellwood Bridge should be very closely managed so that taxpayers get maximum value for their investment. The County and its project team are committed to pursuing cost savings throughout design and construction.

Steel arch chosen for new Sellwood Bridge

The new Sellwood Bridge will feature a steel arch design and cost less than predicted. Multnomah County commissioners chose the structure type for the new bridge and approved a reduced cost estimate in January, agreeing with recommendations from project partners and a citizen advisory committee.

Steel Deck Arch

The bridge replacement project is at the 30% design phase. County commissioners also approved:

• A compressed westside interchange where the bridge connects with Highway 43
• An open bottom concrete arch culvert where a new access road crosses Stephens Creek on the westside
• Stormwater treatment facilities for both sides of the river

Refinements in the design and the reduced size and complexity of the westside interchange have reduced the estimated project cost by $41 million, from $331 to $290 million (in 2014 dollars).

“We often ask our staff to do more with less,” said County Chair Jeff Cogen. “Last fall we asked the project team to design a better project for less money. In this case, we’ve done it.”

Commissioner Deborah Kafoury, whose district includes the bridge, noted that the revised design has the support of local, state and federal partners. “Everyone is on the same page,” she said. “I’m especially pleased we were able to reduce the size and cost of the westside interchange.”

The county board recommended a steel deck arch for the main river span but kept a concrete arch option in the running. A decision on the material type will be made later this year, after a construction firm is hired and final cost comparisons are developed. Bridge construction is expected to begin in July 2012.

County and City complete funding agreement

Multnomah County and the City of Portland have completed a historic agreement to fund the new Sellwood Bridge. The agreement was approved by the Portland City Council on February 2 and by Multnomah County’s Board of Commissioners on February 3.


Mayor Sam Adams addressed the County Board with Marissa Madrigal, Chief of Staff to County Chair Jeff Cogen

The City of Portland will provide up to $100 million to fund the new bridge. Recent project cost savings are expected to reduce the City’s contribution to $80 million. The City’s total contribution will be determined when the project is completed in four to five years. Funds will come from Portland’s share of new transportation revenue from the 2009 Oregon Jobs and Transportation Act.

With the agreement, $270 million has been secured for the project. Other sources include $127 from Multnomah County, $30 million from the state of Oregon, $22 million from Clackamas County, and $11 million from the federal government. Multnomah County is working to secure federal funds for the remaining $20 million needed.

“Frankly, replacing the Sellwood Bridge is something Multnomah County could not have done alone,” said County Chair Jeff Cogen. “We’ve made great progress to replace the bridge because of the partnerships we’ve built with the City, Clackamas County, the state and federal governments.”

“This agreement is an important two-for-one deal,” said Portland Mayor Sam Adams before the County Board voted. “We fund a new Sellwood Bridge and we also close a funding gap for the new light rail line project to Milwaukie.”

The reduced cost of the new Sellwood Bridge will allow the City to contribute $20 million to the light rail project.

“The Sellwood Bridge serves a regional need,” said County Commissioner Deborah Kafoury, whose district includes the bridge. “The contributions from Portland and Clackamas County are essential to funding a new bridge.”

Sellwood Bridge project receives Engineering Excellence award

The Oregon chapter of the American Council of Engineering Companies has honored the Sellwood Bridge project with a grand award for engineering excellence. The project was one of eight to receive a grand award at the organization’s annual awards dinner in January.

Awards are presented to projects led by engineering companies from Oregon and southwest Washington. The Sellwood Bridge project was honored for its recently completed planning phase. CH2M HILL, Inc. led the consultant team during the planning phase, which concluded last year with federal approval of a Final Environmental Impact Statement for the proposed new bridge. Other consultants on the planning team included Alta Planning and Design, JLA, Parisi Associates, and TY Lin International.

The consultant team worked closely with the bridge owner Multnomah County and the community throughout the planning phase. More than 120 alternative solutions were explored. More than 6,500 people shared their views on the alternatives at open houses and through online surveys. One survey allowed participants to “build a bridge” with different components to determine the cumulative impacts and cost of each alternative. The process led to adoption of a preferred alternative for a new two-lane bridge with improved facilities for all modes that has broad community and political support.

On behalf of Multnomah County, congratulations to our consultant CH2M HILL and the other members of the Sellwood consultant team for a job well done.

Clackamas County approves Sellwood Bridge funding

Replacing the aging Sellwood Bridge moved a step closer to reality on December 9. The Clackamas County Board of Commissioners approved a $5 annual vehicle registration fee that will raise $22 million to help replace the bridge. County residents will begin paying the fee in January 2012.

The action adds a critical piece to the project’s funding plan. Another piece of the funding puzzle may fall into place next month. The City of Portland is expected to approve an agreement to fund up to $100 million of the project. With these local funding contributions, the project’s funding shortfall will be reduced to $40 million. Multnomah County has a $40 million request in to the federal government, which would be the final piece of the funding plan.

Traffic studies show the Sellwood Bridge is heavily used by Clackamas County residents. Seventy-two percent of trips across the bridge begin or end in Clackamas County. The bridge lies less than a mile from Clackamas County, which has few other river crossings.




Multnomah County Commissioner Deborah Kafoury thanked Clackamas County Board Chair Lynn Peterson and her board for their critical support. “Clackamas County has been an active partner in this project since it began in 2006. Your elected leaders, staff and citizens have been at the table as alternatives were developed and we settled on a solution. By adopting this fee, you have taken a major step toward resolving this critical transportation need for the citizens of our two counties.”

Read more on the Clackamas County
ordinance and the board’s resolution establishing the fee.

Citizens recommend steel arch for new Sellwood Bridge

After eleven meetings, a committee of citizens has recommended a Sellwood Bridge structure type to a panel of elected and appointed leaders from the region. The verdict? The new Sellwood Bridge should be a steel deck arch with an open deck that does not obscure the view of the green hills west of the bridge.

The recommendation was made at an October 25th meeting with the Public Stakeholder Committee (PSC). Citizen presenters included Heather Koch, Laura Jackson, Jeff Swanson and Paddy Tillett. In recommending the steel deck arch, Swanson noted its benefits.

“It’s within our budget and also reflects our community values,” he noted. “It echoes the character of the historic bridge and enhances views of and from the bridge
“It also performs well on technical criteria,” the Portland Business Alliance representative continued. “It minimizes construction time, traffic closure and risk for in-water work. It also has great potential for local firms to compete to produce parts or construct the bridge. And the arch form really fits the natural setting of this section of the river.”

Jeff noted that the committee’s second choice, the concrete box girder, ran a distant second. “In the words of one committee member, the lower cost box girder is ‘ugly at any price’,” he said.

Citizen committee members also advocated for reducing the size and cost of the westside interchange which would help to lower the height of a rock cut that will be needed to accommodate the new interchange.

PSC members were impressed by the citizens’ recommendations and their efforts to keep within the project’s budget. “I was afraid the citizens would come back with something beautiful that we can’t afford,” noted State Senator Diane Rosenbaum. “Instead you have worked to find the best solution that fits within our budget. This is great work.”

Other comments by PSC members included a suggestion to consider a concrete arch in case steel prices increase during design and a commitment by ODOT to reconsider the need for four through lanes on Highway 43 under the new interchange. Limiting the through lanes to two could lower the cost and size of the interchange.

The PSC will meet in November to develop their own bridge type recommendation for the Multnomah County Board of Commissioners, who are expected to make the final decision in December.


Citizen committee presenter Jeff Swanson describes the benefits of the steel deck arch while Heather Koch awaits her turn to address the PSC.