AFTER MINNEAPOLIS’S I-35W steel truss bridge collapsed into the Mississippi River at 6:05 p.m. on Au-gust 1, 2007, the first job was survivor rescue, followed by recovering bodies and clearing of vehicles and wreckage. Well before that was finished, planning for a 1,223-foot-long replacement structure was under way. The state tallied a daily tab of $400,000 in delay and lost business, given that 140,000 vehicles had been using its eight lanes each weekday. Normally, says structural engineer Alan Phipps of FIGG Engineering Group, a typical bridge of this size takes 30 months to build.

This job would be different. Phipps served as design manager for a team that won a lightning-fast four-way bidding competition. The Flatiron Constructors–Manson Construction joint venture promised to install two concrete bridges—one handling northbound traffic, one southbound —for $234 million. Crews swarmed the site on November 1 to prepare for boring holes and pouring pier foundations at the river’s edge, even as engineers continued to detail the superstructure plans. Taking advantage of the rare fact that this bridge could be built without having to cope with daily highway traffic, crews commandeered the road on the south side of the river to lay out eight precast- concrete assembly lines, featuring four-story-high heated buildings on wheels. These enabled the bridge segments to be cast day and night in defiance of subarctic weather. The crews’ job was to build forms, set reinforcing steel, and pour 120 pieces for assembling the river crossing. The segments measured up to 16 feet in length and weighed up to 200 tons, depending on their location along the gently curving spans. “We couldn’t wait for the four- to six-month lead time to order steel forms, so Flatiron built them out of timber,” says Phipps.

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