MINNEAPOLIS -- The next time you drive down to a Vikings game or the Mall of America, you'll probably notice the brawn of the new Interstate 35W bridge, but you won't really see its brain.
The bridge's predecessor collapsed into the Mississippi River on Aug. 1, 2007, killing 13 people and injuring 145. Construction on the new $234 million bridge began Nov. 1, and it's projected to open as soon as Tuesday, more than three months ahead of schedule.
Four cavernous concrete enclosures underneath the bridge serve not only as its backbone, but also hold the central nervous system for this "smart bridge."
With a guided tour provided by Duluth-based Mesaba Electrical Group, the News Tribune got an inside look at the labyrinth of sensors, electronics and other features in the soon-to-be-traveled, 1,200-foot bridge.
Besides the 750 miles of steel tensioning cable and 50,000 cubic yards of concrete, the bridge will have 323 monitors and sensors to document the bridge's conditions during its lifespan. These gauges, either embedded in the concrete or mounted on the surface, will measure the swaying of the bridge from side to side, the stress points and any bending in the structure. The Minnesota Department of Transportation deemed it a "smart bridge" because of its extensive technology.
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"This is history right here," said Bernie Serre, a Mesaba project manager who also took part in Wednesday's tour. "It's pretty cool, pretty impressive."
The bridge's underbelly, the enclosures that measure 14 feet wide and 19 to 25 feet tall, also house the anti-icing system, which will preemptively spray a solution on the roadway when its electronic weather monitor foresees icy or slippery conditions.
Besides being the central nervous system for the bridge, the four enclosures also serve as its spine, with six cable tension wires lining each box.
Mesaba Electric and its sister company, Polyphase Electric, were responsible for the majority of the electrical work toward the end of construction. From June to August, they had 54 workers putting in long hours each day during seven-day work weeks.
"We made tremendous progress in a short time," said Denny Johnson, Mesaba's on-site project manager. "A lot of people were on top of their game for a long time."
Johnson, who also oversees Mesaba's Waconia bridge project, said his record of hours worked in a week topped out at 114.
"It's going to be hard to go back to normal," Johnson said. "I went to the Waconia bridge, and they hadn't poured one of the fittings yet and I said, 'What?' Here things go quick."
The Interstate 35W bridge project was Mesaba's largest project ever by more than$4 million.
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"We like unusual work," said Tim Harkonen, Mesaba's vice president. "We did $7 million worth of work in eight months. I don't know when we will get that opportunity again. Usually, we do $7 million worth of work in three years."
Southbound travelers on the bridge will again have a tremendous view of the downtown Minneapolis skyline, but now, the view of the bridge from the skyscrapers will provide its own picturesque view.
An aesthetic lighting system of more than 300 LEDs will project any color in the spectrum onto the bridge's white surface. Five lanes of traffic will flow in each direction, two more than the previous bridge, with possible light-rail accommodations. MnDOT said the bridge has a 100-year lifespan.
Starting this week, an average of 141,000 drivers will pass over the bridge every day, comforted by its muscle -- and its mentality.
