I-5 Willamette River Bridge, Eugene/Springfield, Ore.

When Hamilton Construction was asked by the Oregon Dept. of Transportation (ODOT) to be the general contractor on the Interstate-5 Willamette River Bridge replacement project, the firm knew it was going to be a big job. But it didn't realize just how big.

Hamilton, Springfield, Ore., would be taking on a delivery method that it had never before used—the construction manager/general contractor (CM/GC) approach. In fact, ODOT is one of the first five DOTs nationwide to use the method, which involves the owner selecting and partnering with the contractor and designer early on to manage work. Unlike design-build contracts in which the owner hands off the project to the design and construction team, the CM/GC approach keeps the owner heavily involved throughout the project, Hamilton says.

"We were the state agency's personal builder," says Con O'Connor, construction manager and partner at Hamilton. The bridge, which borders the cities of Eugene and Springfield, "was completely different than any other job the firm has taken on; it was unfamiliar territory for us."

The team also cited the CM/GC delivery method for providing flexibility and cost-effectiveness on the project by allowing construction to start two years ahead of schedule while design was under way. This helped the $152-million project finish four months ahead of schedule and $15 million under budget, Hamilton says.

The project involved demolishing the original single-bridge structure as well as a temporary detour bridge and replacing them with twin bridges nearly 2,000 ft long, with 400-ft arch spans—the state's largest.

By comparison, the original, aging structure was 1,800 ft long and consisted of six spans. The detour bridge was 1,985 ft long and consisted of 143-ft main spans of cast-in place (CIP) concrete box girders.

The new bridge is a modern structure built to last up to 100 years. It includes post-tensioned reinforced CIP box girders, prestressed box beams and girders, and a reinforced CIP deck arch.

Done in stages, the project contained three in-water work windows (IWWW), with the first—for pile driving only—lasting from April 1 to April 30. The next IWWW went from June 1 to October 31 for non-pile driving; and the third running from July through October for pile driving again.

The project was complex and included a 120,000-sq-ft work bridge that was built on 263 pilings. It had a steel-reinforced wood deck that served three functions: demolition containment, access for the crews while they were building the permanent structure and support for the falsework construction of the CIP arches. The work bridge was strong enough to support the crews, vehicles, cranes and arch forms, says Jeff Firth, project manager and a partner at Hamilton.

After dismantling the original span, the crew built the southbound bridge. With the diversion of north and southbound traffic to the completed southbound span, the detour bridge was demolished and the northbound span built.

The detour bridge had been built in 2004 after cracking was discovered in the original structure, which resulted in weight limits. But the detour structure was built using materials and methods that could be installed quickly, and it did not meet environmental design or seismic standards for permanent freeway bridges, ODOT says, and so had to be demolished.

Design Input

"There were a lot of stages [on the overall project] that took a lot of thought process," Firth says. "It was complicated to build." Also, citizen groups had an impact on design. "It was a true collaboration," he adds.

With community input, design engineer OBEC Engineering made conceptual designs that the Hamilton and ODOT team used to evaluate cost, schedule and feasibility.

In a nod to the region's history, the new structure includes a 42-ft-long stainless steel depiction of a river and canoe, flanked by camas flowers and cattails that run between the northbound and southbound bridges. The names of the eight Native American bands that make up the Kalapuya tribes, the area's first residents, are etched into the structure's pedestal.

Original plans called for the steel on the southbound work bridge to be reused on the northbound work bridge. But waiting to use the steel from the southbound bridge would have delayed the building of the northbound work span and forced crews to seek a costly variance to extend the IWWW, Firth says.

Hamilton worked with ODOT to find a solution. To keep the project on schedule, the team would build the northbound work bridge prior to completion of the southbound permanent structure. This entailed ordering 1.1 million lb of steel in late spring 2010, which was delivered in early summer of that year. The effort allowed crews to build half of the work bridge with the supplementary steel during the IWWW and complete it with the recycled steel from the southbound work bridge when the IWWW resumed.

Early completion of the work bridge enabled the team to dismantle the detour bridge and do preparatory work on the permanent northbound bridge at least six months earlier than planned. The workaround also helped the project avoid incurring rising steel costs due to inflation, Firth says.

"A delay to the project would have been more costly," O'Connor says. "The initial purchase of steel was more effective."

Firth says that a cost-saving series of value engineering propositions and the CM/GC delivery method gave the team increased flexibility. For example, when local and state agencies as well as the citizens advisory group asked for a new bike path on the south side of the river, a plan that was not part of the project's original scope, the team was able to deliver it.

"The bike path was made possible by redirecting funds made available by cost-savings; the use of 50 salvaged concrete girders taken from the demolished old bridge; and additional federal funds secured by working with Oregon congressman Peter DeFazio, whose district is home to the bridge," Firth says. He adds that the cost-savings from using the salvaged beams was significant.

The team also faced multiple external terrain features that were undesirable for a construction site. These included arterial roadways, wetlands, a main rail line, a freeway off ramp and two parks. "This was not your normal urban interchange," Firth says.

The project included eco-friendly practices, one of which was to build a water runoff containment system as part of the work bridge. The system, which prevented demolition debris from falling into the river, stayed in place until the work bridges were removed.

The team also used a hydro-acoustic noise attenuator, also called a "bubbleator," during pile driving to diffuse underwater sound levels. Two 1,600-cu-ft-per-minute compressors vaporized the water to create an air curtain and minimize fish disturbance. This was also the ODOT's first use of recycled cement. The material was used in a commercial mix application and in the large mass footing pours.

"There was a lot of innovation that took place on this project and especially in the development of concrete mix designs," Firth says. One of ODOT's goals was to provide sustainable, cost-effective solutions that exhibited performance durability, and "the use of recycled concrete certainly met all those objectives," he says. "We were able to remove thousands of pounds from the waste stream."

Other environmental elements included the use of canola oil biodiesel for the pile drivers. Compared with petroleum-based diesel, canola oil reduces carbon monoxide emissions by 30%, Hamilton says.

Also, the new bridge touches down in only one place—a natural island in the river. By comparison, the old bridge had five piers and the detour bridge had 21.

The team used the Freyssinet method employing reinforced concrete truss spans on the new span. Firth says this is the state's first use of the method since 1932.

In naming this project the region's best, the judges applauded the team's safety efforts, with one saying that there were many preventative measures taken. These included a health and safety program tailored to the project.

The program addressed a range of potential hazards. PCA Health & Safety Consultants was hired to employ a full-time safety crew on site that worked closely with Hamilton's safety and operations staff. Routine job hazard analysis was conducted along with daily safety huddles, weekly "toolbox talks" and monthly safety meetings with the subcontractors.

Onsite visitors were also required to participate in a safety orientation program.

At peak, the project employed 80 Hamilton workers and about 200 to 250 subcontractors on site. Throughout the 351,192 total hours worked, there was one lost-time injury on the job.

The safety judges noted that record in giving the team the Excellence in Safety Award.

The judges also took special note of the team's efforts to mitigate risks to the environment and to reach out to the community and the local tribes. They also commended the team's collaboration and the bridge's "elegant" design.

Key Players

Owner/Developer Oregon Dept. of Transportation