Speed and Strength

On Aug. 1, 2007, the I-35W bridge over the Mississippi collapsed into the river. The Minnesota Department of Transportation (Mn/DOT) issued a request for qualifications for the replacement bridge Aug. 4. A request for proposals (RFP) was released Aug. 23. On Oct. 8 Mn/DOT affirmed its selection of design-builder Flatiron-Manson Joint Venture (F-M) to receive the rebuilding contract. By Christmas Eve 2008, the reconstruction of the new St. Anthony Falls (I-35W) bridge should be complete.

Flatiron and Manson have experience working together, having recently completed the San Francisco Oakland Bay Bridge Skyway as a joint venture. Flatiron has worked with their lead designer, Figg Bridge Engineers, on projects such as the Sagadahoc Bridge in Maine. The key team members bring years of experience in both bridge design and construction and fast-tracking projects.

Quality Assurance

To keep to Mn/DOT’s aggressive schedule, construction will take place on three fronts simultaneously, including in situ construction of the concrete side spans. F-M has a quality management plan and an integrated quality approach that they expect to enable them to meet or exceed Mn/DOT’s expectations. A quality performance incentive plan will reward those working on the project and ensure a premier final product. Bimonthly quality evaluation meetings between F-M and Mn/DOT will keep them on track for those goals.

“For the main bridge, they’re going to be building the approaches … and at the same time casting segments of the main river span,” says Jay Hietpas, Mn/DOT design-build program manager. “So they’re able to work on multiple areas at one time.”

Aesthetics

The F-M team has chosen a theme of “Arches, Water, Reflection” as the source for their designs. A number of choices for the new bridge’s appearance have been submitted, and the community will be involved in the final selection. The basic design will have a concrete box girder variable depth superstructure and a parabolic curve over the Mississippi. The aesthetic features to be selected will include pier shape, railing details, color, textures, gateway monuments, and feature lighting. A site memorial will also be part of the design, to be developed in three evening charettes. The design also has provisions for a future pedestrian walkway underneath, if needed.

“We asked each team to come up with their own design and their own aesthetic approach to it, so we asked them to look at the context of the surrounding environment,” Hietpas says. “There’s a lot of arches in the area, so they kind of incorporated the theme of the surrounding environment and incorporated an ‘arch’ approach to their concept.”

Ultimately, he says, they wanted the bridge to blend into the surroundings but also wanted it to be an elegant, modern bridge.

In addition to the actual bridge design, the proposal includes landscape design in the park areas on both banks of the river which, among other things, means plantings, walkways, lighting, side grading, signing, site furnishings, and vehicular and pedestrian circulation. The plan preserves existing natural features and a historic stone wall. There are observation decks on both sides of the river, adding to the park’s atmosphere. It also includes a provision for future changes to the park area by the National Park Service and City of Minneapolis.

“Some people in the community want the bridge to be a showcase, and some people in the community say, ‘No we want to fit into the environment,’” Hietpas says. “It’s kind of a delicate balance.”

Structural Enhancements

The old bridge was a non-redundant structure. “This bridge will have multiple levels of redundancy,” Hietpas says. “We required a minimum of three [concrete box] webs on the design; they have a minimum of four webs.”

The design will incorporate a number of innovative materials to minimize life-cycle costs. It will be built of high-performance concrete, including a corrosion inhibitor. Extra ducts and anchors will allow for future post-tensioning so that the live load can be increased by 10 percent. An integrated sensor and monitoring system will allow Mn/DOT to get bridge information in real time. There will be only two expansion joints for low maintenance and ease of inspection.

Community Relations

Hietpas and the team will actively disseminate information to the public and involve the community in the project as it proceeds. In addition to the preliminary design charettes, during construction there will be sidewalk superintendent talks, three bridge kiosks with interactive monitors, Web cams, and an outreach for education initiative. In addition, construction operations near residential neighborhoods will take place during the day, minimizing noise problems for the residents.

For Mn/DOT, this is their seventh best value design-build project.

”This was a little bit unique, where the highest price actually was awarded the project,” Hietpas says. “Before, in the past, the lowest prices had the highest technical score — in general — but on this job, there was quite a big spread in the point difference [in the] technical scores.” Even though Flatiron’s cost was quite a bit higher than the other teams, they were still awarded the contract, based on their approach. “When we scored them, we didn’t score them on time, and we didn’t score them on cost,” he says. “Those elements were sealed when we actually scored the proposals.”

In addition, Hietpas says this project was different in other ways. “The previous ones we were pretty prescriptive in what actually the scope of the project was,” he says. “We said, ‘You pick the profile. You pick the alignment. You pick the bridge type. You pick the aesthetic approach you want to use.’”

Another unique aspect of the bridge project is that it will be the first built under the Federal Highway Administration’s (FHWA) Design-Build Rule.

The Rule, Section 1503 of the 2005 Safe, Accountable, Flexible, and Efficient Transportation Equity Act - A Legacy for Users (SAFE-TEA-LU), requires that FHWA allow state departments of transportation design-build projects to proceed through the preliminary design phase before the National Environmental Policy Act (NEPA) process is complete. This streamlines the preliminary design phase by allowing it to run concurrently with the NEPA review. The final design phase cannot begin until the NEPA review has been concluded. DBIA submitted comments when SAFETEA-LU was being considered.