Minneapolis I-35 Bridge Reopens ahead of Schedule

Elizabeth Taurasi, Executive Editor -- Design News, September 18, 2008

Three months ahead of schedule, the new I-35 bridge in Minneapolis opened to traffic this morning. The bridge collapsed on August 1, 2007, killing 13 and injuring 145 others.

The Associated Press is reporting the new $234 million structure contains hundreds of sensors to collect data. This "smart bridge" technology, according to the AP article, is to detect small problems before they become big ones. The concrete is embedded with more than 300 sensors that will generate a record of how it handles the stresses and strains of traffic, along with Minnesota's harsh climate, the AP article says. The sensors will also measure how the structure will handle loads and vibrations and how it will expand and contract between winter and summer seasons, as well as watch for any potential corrosion from rock salt and other road treatments.

The new bridge was completed ahead of its Dec. 24 schedule, which will allow for the contractor to reap a reported $27 million bonus.

While the old bridge was built from steel, the new bridge is concrete and built with redundant systems to keep the structure from collapsing should one part fail.

The contract to rebuild the bridge was awarded Sept. 19, 2007 as a joint venture between Flatiron Constructors Inc. and Manson Construction. Flatiron-Manson had the highest technical score out of the four bidders.

A National Transportation Safety Board report released last march determined the bridge collapsed under the weight of tons of sand and construction materials stored at two of the structure's weakest points. NTSB officials said in January serious design flaws in the size of several gusset plates used in the main truss of the 40-year-old bridge was a "critical part of the failure."

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