e-Mail

Print

The Oregon Department of Transportation (ODOT) currently is undertaking the largest bridge replacement project in its history. The new Interstate 5 Willamette River Bridge will be a milestone for ODOT in many respects, most notably for its use of the construction manager/general contractor (CM/GC) procurement method — an ODOT first.

Now that construction has been under way for several years, the project team offers insights on CM/GC. Ray Mabey and Jim Cox manage the project for ODOT, Jeff Firth oversees construction for Hamilton Construction, and Larry Fox leads the designers for OBEC Engineering. Each brings more than 15 years of experience in construction or design management, and sometimes both, to this project.

Q: How exactly does the CM/GC procurement method work?

Cox: First, ODOT selects the design and CM/GC firms, which then work as a team with ODOT to build the bridge from start to finish. The CM/GC provides input to design and vice versa. The CM/GC model allows ODOT to have significant input and control throughout the process. All three parties work together to address problems and opportunities efficiently throughout the project’s life cycle.

Q: How does CM/GC differ from more traditional delivery methods, such as design-build and design-bid-build?

Mabey: CM/GC and design-build both benefit from collaboration between the engineer and contractor. But in design-build, the owner contracts directly with the design-build team and thus is not in the center of the contractor-engineer collaboration. This gives the owner much less control over the project.

Another major difference is that in design-build, the owner mitigates, accepts, or passes risk on to the design-build team. If the owner decides to pass on the risk, the design-build team has to price the risk. In CM/GC, we have the contractor strip risk from the price, and we as the owner can hold the price of risk as a contingency. If the risk materializes, we expend the funds; if not, we keep them.

Compared with design-bid-build, CM/GC has many benefits. Design-bid-build is a linear process: design, permits and right of way all need to be complete and acquired before the project is put out for bid. With CM/GC, the project can be fast-tracked — elements whose design is complete can be constructed while design continues on others.

Fox: The CM/GC method allows designers and the owner to get the benefit of collaborating with the contractor during the design development. We can design in means, methods, and efficiencies to provide better value and risk management for the project. It is similar to design-build; however, it is very hard for the owner to retain control of design decisions on design-build projects. With CM/GC, the owner makes all final design decisions after weighing the costs and benefits.

Firth: Compared with the other delivery options, CM/GC allows the general contractor to critique the A&E’s design to make the project easier to build, which can result in cost savings that are passed along to the owner. In a sense, you are constantly value engineering during the process. Through this process, the contractor can help the owner price risk so they can better evaluate what risks it wants to take.

Cox: CM/GC allows ODOT to balance stakeholder desires with project budget. For example, on the Willamette River Bridge, the community wanted input on the style of bridge being built. The designer, contractor, and ODOT worked together to select a bridge type, with Hamilton providing input on cost, schedule, and feasibility, and OBEC modifying design based on community needs. This kind of collaboration continues on this project because of CM/GC.

The arches on the Willamette River Bridge are not true arches — their rise is too flat. To minimize bending forces and induce compression into the arches, the design calls for the arch halves to be jacked apart at the peak.

Q: Why did ODOT choose this delivery method for this particular project?

Mabey: In large part because of its complexity. Not only is it the largest bridge replacement in the agency’s history, it also has the potential for major environmental and community impacts. ODOT needed to control final design decisions so it could respond to the many community-related and environmental issues this project was destined to encounter.

Cox: Additionally, compliance with the National Environmental Policy Act required the preparation of an Environmental Assessment for the bridge. By the time the Finding of No Significant Impact was signed, there were about four years left to complete design and construction before the legislatively mandated completion of the OTIA III program. To meet that deadline, project construction had to be accelerated. Design-build would have allowed us to accelerate construction, but at the cost of having limited ability to make design changes after the contract was awarded. CM/GC gave us both the benefit of project acceleration and final design approval.

Q: What do you see as the greatest benefits of CM/GC for the A&E firm?

Fox: Well, for one, designers working on the project learn how contractors approach their work, what’s important to them, and where costs lie. Since you can collaborate with the contractor during design, you can more likely incorporate innovative and complex engineering into the project because the contractor ensures the designs you are proposing can be built. In short, it makes designers better engineers.

Q: Larry and Jeff, as heads of design and construction, have you witnessed any particular times on the Willamette River Bridge project where the CM/GC team helped solve a challenging design or construction problem?

Crews prepare to pour the deck of the southbound bridge. The southbound structure is expected to open to traffic in late August 2011.

Fox: One good example is the site where the two arch ribs meet at a single juncture in the middle of the river. That particular joint between the two arch ribs and the foundation was extremely congested due to the amount of steel reinforcement all coming together and overlapping in a very confined area. Hamilton was concerned about its ability to place the rebar with the accuracy required to have it all fit together, as well as the difficulty the crews might have getting wet concrete to flow and consolidate properly to ensure the arch bases had no voids when they removed the forms.

The designers and the CM/GC collaborated to solve these issues and came up with two innovative measures. The engineers designed and detailed steel plate templates to assist in accurately placing the rebar. We also collaborated with the contractor and with the ODOT Materials Lab to develop a high-slump concrete mix for this area of the bridge that allowed for consolidation of the wet concrete around the highly confined spaces between the rebar and the forms.

When they took the steel forms off after the concrete was poured and cured, we had a perfectly built result: The parts fit together like a good Swiss watch. And all this with no claims from the contractor, which would have been a very likely outcome under the same circumstances in a traditional design-bid-build contract.

Firth: Another innovation occurred because the bridge crosses the Willamette River, so we were required to work within limited in-water work windows for driving pile. The designer, the agency, and my team wanted to minimize the impacts to the wild as much as possible, and because we were able to make changes once construction began, the team decided to create a noise attenuator that exceeded the established requirements for pile driving. This noise attenuator, or “bubbleator,” protected fish populations from hydroacoustic impacts that can negatively affect their communication and migratory patterns.

Q: What are the biggest advantages of CM/GC for the construction firm?

Firth: Being able to give input to the A&E and the owner on design, specifications, traffic staging, and environmental aspects of the bridge; being able to begin construction prior to having design 100 percent complete; and having the flexibility to limit risk to both the construction firm and the agency.

Q: Was there a challenge the agency faced during the development and construction of this project so far that the CM/GC helped solve?

Cox: When the agency was developing the type, size, and location of the new Willamette River Bridge, we decided to use a dynamic public involvement process that required immediate responses about construction impacts and pricing. The CM/GC quickly and accurately provided us with necessary information to keep the public process moving forward. This same interaction carried us into the local, state, and federal permitting processes, allowing us to move quickly into building the initial structure: the temporary work bridge.

Mabey: The selected bridge type for the Willamette River Bridge calls for a deck arch design. True arches theoretically experience compression only, no bending forces. The arches on this project are not true arches — their rise is too flat. To minimize bending forces and induce compression into the arches, our design calls for the arch halves to be jacked apart at the peak. The jacking forces and distance were calculated; however, when executed on the southbound bridge arch spans, the distance was different from what we had anticipated, causing changes to the spandrel columns that support the deck. Normally, in design-bid-build, the contractor would consider that a change and would expect compensation to accommodate it. Anticipating the possibility, our CM/GC contractor was able to adapt without needing to request a change in compensation or time, which allowed us to stay on time and on budget.

Q: What have been the biggest challenges in using the CM/GC delivery method? Are there any downsides?

Cox: The partnership between the owner, A&E, and CM/GC is heavily dependent on the qualifications of each, but it is even more dependent on the ability of the parties to work collaboratively. If one of the parties is not a good partner, the process can suffer immensely. Where there have been issues, we’ve worked with the principals to make adjustments. Additionally, the agency’s change order process was not set up for the early work package processes required by CM/GC; we have created a working arrangement specifically for this project to resolve that challenge.

Firth: The biggest challenge has been on the contracting side versus the construction side — getting scopes identified, method of payment, proper plans, and specifications to align with those scopes. The biggest downside is trying to capture all the work that is necessary in a specific design package; it takes a lot of foresight when identifying scopes of work.

Q: Based on your experience on the Willamette River Bridge project, would you recommend CM/GC for other construction firms?

Mabey: Yes. Flexibility in delivery methods allows an agency to be responsive to different project challenges, making it more versatile. I expect more departments of transportation will use CM/GC in the future.

Firth: It depends on the project and timelines. For a small project of short duration, CM/GC probably isn’t the way. If it is a larger, more complex, longer-duration project with many local governmental agencies and stakeholders involved, CM/GC is the way to go.

Fox: CM/GC is a great delivery method for large, complex projects where contractor input is essential to assist in design development as well as to manage risks along the way. I think it would be a great experience for all design firms to have, assuming they have the staff capable of pulling it off.