Located in the center of the Willamette Valley in central western Oregon, the city of Corvallis has a population of 61,000 and is nearly equidistant to Salem in the north and Euguene in the south. Its central location increases the importance of infrastructure projects like the Van Buren Bridge replacement. The Oregon Department of Transportation (ODOT) and Hamilton Construction are currently working on the bridge, which spans the Willamette River in Corvallis.

The old Van Buren Bridge was built in 1913 and serves eastbound traffic. A partner bridge, Harrison, serves westbound traffic. Just 20 feet wide, the Van Buren Bridge was a two-lane swing bridge that was converted to a single lane for modern traffic.

The route leading onto the bridge is three lanes and experiences significant backups during rush hour as traffic funnels into one lane. The bridge has an average daily traffic of 13,000.

The bridge was recently load-restricted, preventing most freight traffic from using it. Fire trucks and school buses were also not permitted on the bridge.

"The Van Buren Bridge had details which are fatigue prone," said Andy Howe, a Bridge Design Engineer with DOWL, the designer and engineer for the project. "It had spans that lack redundancy and was a swing bridge that was no longer able to open."

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The last reason the old Van Buren Bridge needed to be replaced was to have a bridge that could survive an earthquake. The bridge is in the Cascadia Subduction Zone, a more than 700-mile fault line.

"There have been 43 earthquakes in the last 10,000 years within this fault,” Howe said. “The last earthquake that occurred in this fault was on January 26, 1700, with an estimated 9.0 magnitude."

While no one can say with certainty if another powerful earthquake will occur in the area, ODOT is taking the possibility seriously and is designing infrastructure to withstand large earthquakes. This consideration has been part of the ODOT mindset since the 2000s.

"When this bridge is completed, it will be the only bridge over the Willamette River in the mid-Valley that is expected to be operational after Cascadia," Howe said. The next closest seismic resilient bridge is 60 miles away on the north side and 40 miles on the south side.

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Engineers designed the bridge to be serviceable within 48 hours after a magnitude 9.0 earthquake. Inspectors would need to review approaches and determine what/if any repairs need to be made.

"We built two temporary bridges to construct one permanent bridge," said Markus Schaaf, an ODOT Assistant Resident Engineer managing the construction contract. The first temporary bridge serves as a detour bridge during the demolition of the existing bridge and construction of the new one. The team also built a work trestle to facilitate demolition and construction access.

The team put great thought into where to land the west end of the bridge. There is significant commercial activity off the west end of the bridge, as well as the Riverfront Commemorative Park. The nearly 12-acre park serves as a community gathering place and regularly hosts activities.

"We needed to preserve the function of the existing street system to continue the current use in that area," Howe said.

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The new bridge is 730 feet long and has three main pieces. There is a short span on the west bank, three spans over the river (approximately 615 feet), and a short steel span to get back down. The three main spans of the bridge are haunched steel (which was economical and provided the required clearance) and plate girders with a concrete deck

"This structure type was selected specifically to land the bridge at 1st Street while being able to clear the Coast Guard river navigation envelope,” Howe said. "We're replacing a swing bridge with a fixed span. Navigation of the river by large vessels is uncommon these days, but that function needed to be preserved."

The new bridge is 52 feet wide and includes two driving lanes and a shared-used path. The old bridge had a bumpy, wooden path. Schaaf said the path was so bumpy that bicyclists would ride in the driving lane. The new shared-use path is suitable for cyclists and walkers.

Designing a bridge that can withstand a magnitude 9.0 earthquake can come with many challenges. One that the design team ran into was that the west riverbank is potentially unstable during powerful earthquakes. Soft soils in the area extend to great depth, and the soil at the bottom of the river may liquefy during a large earthquake. Howe explained how the design compensates for the soft soils.

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“We used isolation bearings within the bridge to address the difference in behavior between the foundations in the river and the foundations on the riverbanks,” he said. “The middle part of the bridge will sort of float independently from the ends. This feature means unique bearings and unique expansion joints in the deck. Seismic design code requires the foundations to be more robust than the columns that support the bridge. We want any damage during an earthquake to be easily seen rather than hidden below the ground surface. As a result, the drilled shaft foundations are 8 feet in diameter and use a thick permanent steel casing in the high-stress area. The limited friction between the steel and the soil means shafts extend more than 200 feet below the bottom of the river.”

Constructing the deep foundations was a challenge for the team. Hamilton Construction Manager Pat Prescott said that the shafts approached 240 feet, which presented some constructability challenges with reinforcing cages, site logistics, and water management. The team constructed shafts using an oscillator capable of exerting 8 million pounds of torque.

"The powerful torque allowed our subcontractor to install and remove casing that was necessary to get the work done quickly and create secure and stable shafts at a reasonable price," Prescott said.

Any time construction occurs around a waterway, teams face restrictions regarding when they can work in the water. The Van Buren Bridge project had bird windows, in-water work windows, and limited roadway closures. Each of these played a part in the planning process.

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Hamilton Construction, headquartered in Springfield, Oregon, has previously worked with ODOT.

"They have a good reputation and have proven it on this project,” Schaaf said. “They're organized and prepared and ask questions early on as they are ahead, which allows us to react before crunch time." He added that there is a sense that everyone has the same goal and is working as a team.

Prescott seconded that notion. "We've overcome and solved problems through great communication and everybody's willingness to have a quick conference call or meeting to discuss the challenge at hand,” he said. “The sooner an issue is identified, the more time you have to collaborate and come up with a solution." He added that with a "project first" mentality, challenges are resolved and overcome quickly.

Besides having the low bid, Hamilton also has been a good choice because they own a significant amount of temporary steel. The need for temporary steel and Hamilton's experience in bridge construction have empowered them to handle the project successfully.

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DOWL has also worked with ODOT. DOWL and Hamilton were both involved in the successful Willamette River Bridge project in Eugene, Oregon.

The $61.4 million project (construction costs only) is on budget. The federal government is paying 89 percent of the costs, while the state government is paying the remainder.

Construction on the project began in spring 2023 and is scheduled to conclude in December of 2026. Currently, the project is slightly ahead of schedule. Prescott and Schaaf credit the teamwork of all associated with the project as one of the prime reasons for being ahead of schedule. In addition, the team is on site six days a week and up to 16 hours a day. Forward-thinking is another reason for the team being ahead of schedule.

"We're all about communicating the work, planning the work, and thinking long term," Prescott said. "Our crews need to be fully aware of what is going on this week and the next, but we have to keep our eye on schedule three, four, six months from now.”

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Upon completion of the Van Buren Bridge project, drivers will have two eastbound lanes leaving downtown Corvallis and no-load restrictions. Pedestrians and bicyclists will have a new shared-use path on the bridge. Finally, the earthquake-ready bridge will keep the area from being cut off if an earthquake occurs. Reliable transportation will aid local and regional recovery for potential earthquakes.

• Owner: Oregon Department of Transportation
• General Contractor: Hamilton Construction, Springfield, Oregon
• Designer/Engineer: DOWL, Bellevue, Washington
• Other Key Contractors: Willamette Valley Excavating, Albany, Oregon (excavation/roadwork); Michels Construction, Brownsville, Wisconsin (drilled shafts); Aaken, Bend, Oregon (electrical); Knife River Northwest, Bismarck, North Dakota (paving/concrete supplier); Riverbend Materials, Eugene, Oregon (concrete supplier)
Photos courtesy of Oregon Department of Transportation