I-35 Bridge: Responding to Tragedy

  • Client:
    Manson Construction Company
  • Completion Date:
    September 2008
  • Key Collaborator:
    Flatiron
  • Project Type:
    Marine Infrastructure
  • Service Categories:
    Owner Services & Onsite Support
    Naval Architecture
  • Challenge:
    Engineer bridge replacement and equipment logistics on a deadline.

A TIGHT CHANNEL AND A TIGHT SCHEDULE.

The I-35 bridge was over 2,000 feet long and crossed the Mississippi River in the middle of Minneapolis. On August 1, 2007, it collapsed in the middle of rush hour, claiming the lives of 13 people and injuring over a hundred more. In immediate response, civilians from all over the region took action to help in the rescue efforts. Within three hours of the bridge’s collapse, the rescue mission was complete. Minnesota DOT swiftly called for a replacement bridge with a far safer, superior design.

The Minnesota DOT selected the Flatiron‑Manson Joint Venture to design and build the replacement. The project kicked off the just days after the bridge’s collapse and the entire team was given just 15 months to open the new bridge. Glosten was contracted to design the crane barge to support the bridge segment lifts. The navigation locks on this upper part of the Mississippi are only 56 feet wide, which is too narrow to fit a single barge large enough to support the crane. The team opted to assemble a raft of two smaller barges connected with a grillage to perform the lift.

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QUICK THINKING.

Glosten evaluated prospective barges and alternative lifting schemes and developed a finite element model of the barges and grillage to analyze a full range of load conditions to safely pick, lift, and place the bridge segments. Two 54-foot-wide barges were joined on site by a steel grillage to support the Manitowoc 4600 ringer crane and provide enough stability for the lifts while still managing to fit through the channel’s locks. The crane was acquired in the Pacific Northwest and was disassembled at Manson’s Seattle yard, trucked to Minneapolis (in over 40 truckloads) and reassembled on site. The grillage was fabricated in two halves, brought upriver on the chartered barges, and finished on site.

The joint venture team exceeded the DOT’s goal timeline and opened the new St. Anthony Falls Bridge three months ahead of schedule, finishing the entire project in just 11 months.

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