Hundreds of sensors give U of M officials valuable data about the 35W bridge

One of the legacies of the 35W bridge collapse, which occured 11 years ago this week, was a focus on the safety of the nation’s bridges.

That includes the bridge that replaced the structure that collapsed. It’s now monitored by 500 sensors.

Researchers at the University of Minnesota say it’s one of the few, if not the only bridge, that has this many sensors monitoring it for so long. The sensors will be in place 10 years next month.

Those insights from the data are helping them better understand how bridges work and they're making them safer.

Underneath the vehicles that cross the 35W St. Anthony Falls bridge every day are these sensors. Think of them as automated inspectors.

“There are emails that go out every week from the bridge that say the monitoring system is operational,” said Lauren Linderman, of the University of Minnesota’s Civil, Environmental and Geo-Engineering Department.

The system sends researchers like Linderman information in the form of emails on how the system is working.

“This is kind of an unique opportunity,” she added.

Linderman is on the team that looks at the data to find clues on how the bridge is holding up over time.

“Usually there’s not an immediate change,” she said. “It’s a slow change in the performance of the structure.”

According to the National Transportation Security Board, a faulty metal plate on the old structure was the likely cause of the collapse on Aug. 1, 2007. The collapse killed 13 people and left 145 others injured.

Inadequate inspections were cited as a contributing factor.

The sensors on the new bridge, completed just 13 months after the collapse, go a long way toward addressing that problem. They measure factors like displacement, vibration and temperature.

“Structures kind of breathe regularly with temperature and just time and so if you drive, you might see a gap for a bearing, well that allows it to move horizontally,” said Linderman. “So, the current system measures that to make sure that’s operating properly.”

So far, researchers haven’t seen anything in the data that has prompted concern, giving them room to focus on other areas.

“To try and improve the long-term performance and serviceability of structures, to try and improve the economic impact of them and try to preserve them,” Linderman added.

The researchers are working with MnDOT officials on a 10-year review of the system, figuring out what works and what does not.