The I-35 bridge was over 2,000 feet wide 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 immediate action to help in the rescue efforts. Within three hours of the bridge’s collapse, the rescue mission was complete. Following suit, Minnesota DOT swiftly called for a replacement bridge with a far safer, superior design.
A Tight Channel and a Tight Schedule
The Minnesota DOT selected the Flatiron‑Manson Joint Venture to design and build the replacement, kicking off the project just days after the bridge’s collapse. Glosten was contracted to design the bridge segment lift sequence and grillage, and the entire team was given just 15 months to open the new bridge. Because the navigation locks on this upper part of the Mississippi are only 56 feet wide, they were too narrow to fit the new grillage or a barge large enough to perform the lift.
Glosten evaluated prospective barges and alternate lifting schemes, and developed a finite element model of the barges and grillage to analyze for a full range of load conditions to safely pick, lift, and place the bridge segments. Two 54-feet wide barges were joined on site by a steel grillage in order 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 disassembled at Manson’s Seattle yard, trucked to Minneapolis (over 40 truckloads) and reassembled on site. The grillage was assembled in two pieces, brought up river on chartered barges, and finished on site.
A Job Done Well, Ahead of Schedule
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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