Launch Slideshow

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Bridge from Tragedy

Bridge from Tragedy

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    The St. Anthony Falls Interstate 35W bridge is 76 feet wider than its predecessor and can accommodate the addition of light rail. Redundancy is designed into every element of the structure. Photo: Joe Nasvik

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    Twin City residents were invited to meet with project mangers like Minnesota DOT's Jon Chiglo (on the left with safety vest) every Saturday to learn about the reconstruction progress. Attendance ranged from four to 450 people; ultimately, 5,000 members of the public took advantage of the “sidewalk talks.” Photo: Joe Nasvik

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    Award-winning mathematicsMinnesota DOT's formula for determining the technical score of “best value” design-build proposals.

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    Flatiron/Manson cast the back-span sections of the bridge in-place and used precast segmental construction for the main spans, making it possible to work on all portions of the deck at the same time. They used the I-35W roadway south of the river as the site for the segmental precasting beds. Photo courtesy of Figg Engineering Group

To design and build the bridge in one-third the time Minnesota DOT typically allows for such a project, Flatiron/Manson orchestrated a well-choreographed ballet of innovative engineering with just-in-time materials delivery involving multiple players. For a detailed explanation of construction, see “Bridge to the Future” in September's CONCRETE CONSTRUCTION.

The Aug. 1, 2007, collapse of the eight-lane Interstate 35W bridge into the Mississippi River made headlines worldwide when it killed 13 and injured 145. In addition to shocking the nation, the failure shocked the Twin Cities' economy.

Opened to traffic in 1967, the structural steel bridge was a vital cross-town link between Minneapolis and St. Paul. Each day it remained closed, road users lost an estimated $400,000. Faced with a grieving and angry public, Minnesota DOT (Mn/DOT) released its seventh “best value” design-build request for proposals.

Four construction companies aligned with engineering and/or design firms to tackle the challenge. A panel of experts convened by the department evaluated each based on price, construction time, design, quality, safety, and technical content. The request for proposals was issued Aug. 23, 2007; the contract was awarded Oct. 8; construction began Oct. 15; and a test shaft was drilled Nov. 1.

Contracted to be completed in 437 days for $234 million, the new St. Anthony Falls I-35W bridge was completed 90 days ahead of schedule, earning the joint venture of Flatiron/Manson $25 million through an early-completion bonus and a “no excuses” clause in which it relinquished all rights to future claims.

THE RULES OF THE GAME

The financial incentives were separate from the methodology Mn/DOT used to evaluate proposals. The department's formula for best-value design-build contracts is mandated by state law and didn't produce the lowest-priced option.

In fact, Flatiron/Manson's proposal was the most expensive. But when its technical score, which was almost 24 points higher than the nearest competitor, was factored into the equation, the result was the lowest adjusted score — and thus, the “best value” option.

Mn/DOT Project Manager Jon Chiglo says the department gives away some control to give bidders considerable latitude and flexibility. In this case, the department provided geometric layout, with no horizontal or vertical restrictions beyond minimum height requirements for barge traffic; environmental requirements; drainage requirements; and a completion deadline of Dec. 24, 2008.

He likes this approach because it makes safety a high priority, emphasizes quality as well as price, integrates design into the bid process, allows Mn/DOT to evaluate the experience and approach of the design-build team as part of the selection process, gives the contractor more control over the project schedule, and enhances partnership all around.

It also allows the department to consider candidates' approaches to “non-tangible” items like public involvement and aesthetic enhancements. Bidders were required to explain how the public would contribute to design decisions. They also were invited — but not required — to resolve six substandard geometric design elements in the original roadway approaches to the bridge.