A barge on the Mississippi River transports precast segments to the jobsite.
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The concept of Best Value Design/Build is at the heart of the I-35W bridge project's success. Along with providing a durable structure, designed and built to serve the public for more than 100 years, the new bridge has a graceful, elegant modern design. It is positioned for growth, as the new bridge is 76 feet wider than the old one and will accommodate significantly more traffic and possibly light-rail transportation in the future.
Best Value contracting encourages everyone involved in the construction, including the owner, to focus on building the best quality possible. Jon Chiglo, the project manager for the Minnesota Department of Transportation (Mn/DOT), says, the I-35W bridge was their seventh Best Value project. And for producers, it showcases a performance approach to specification writing.
Shortly after the collapse last summer, Mn/DOT invited construction companies to submit “Best Value Design/Build” proposals for the reconstruction. For the contractor, deciding to bid a Best Value Design/Build project imposes additional responsibilities. Each bidder was required to provide its own design for the bridge, so they approached bridge design/engineering firms to work with them. Because the contractor is responsible for the design, they are not entitled to change orders based on material or labor quantity overages or design conflicts.Best Value bidding
There were three bid sections for this project: price, time, and Best Value, said Terry Ward, Mn/DOT's deputy project manager. In the Best Value section, the important areas included safety, quality, public relations (including public involvement in the design process), aesthetics, and enhancements. The upfront costs of Best Value contracts are often a little higher than traditionally bid projects. But over the life of a contract there is minimal cost growth due to change orders, and the final numbers turn out to be close to other forms of bidding.
Four bidders submitted bids after one month, during which they conducted research, completed designs, and presented their proposals to the review panel. There were three proposals for structural steel bridges and one for structural concrete.
A panel of experts convened by Mn/DOT evaluated each proposal on the basis of price, time to construct, design, quality, safety, and the proposal's technical content.
In October, Mn/DOT awarded the contract to the joint venture of Flatiron Constructors, Longmont, Colo., and Manson Construction, Seattle—with FIGG Engineering Group (FIGG), Tallahassee, doing the design work and being the engineer of record. The winning proposal was the only one submitted for a structural concrete bridge.
Flatiron was the 70% partner and provided leadership, scheduling, and organization. The contractor self-performed many aspects of the construction, including concrete work. Manson was the 30% partner with expertise working on water and with large cranes. Its responsibilities involved transporting the precast segments by barge and lifting them into position using a 600-ton “ringer” crane mounted on two barges in the river.
The bridge is actually two bridges—one for each direction of travel. To further speed construction, the venture decided to cast the back-span sections of the bridge in-place and use precast segmental construction for the main spans, making it possible to work on all portions of the deck at the same time.
With this approach, the contractor could double up its efforts. For example, contractors typically buy one set of bridge pier forms, constructing one pier at a time, says Ward. But on this project, the contractor bought enough forms to construct all substructure elements at the same time. Also, contractors typically set up one or two casting beds onsite to produce precast segments. But here, eight casting beds were set up.
Flatiron's managers decided to use structural concrete because they would stand a better chance of completing the bridge on time and have better control of their very tight schedule.
—By Joe Nasvik, senior editor with CONCRETE CONSTRUCTION, TCP's sister publication.