Electronic Design

Engineering Bridges Isn't Just Civil Anymore

During my days as an engineering student at Manhattan College, my calculus teacher used to say, "No partial credit! Get wrong answer, bridge fall down!" This was the first thing that flashed through my mind back in August when I heard about the I-35W bridge collapse in Minnesota. My very next thought was that an error in calculations couldn't have been the cause of this disaster. So what was the cause?

The day after the collapse, Michael J. O'Rourke, a professor of civil and environmental engineering at Rensselaer Polytechnic Institute, said in a New York Times article that the bridge's renovations likely caused the collapse, not general decrepitude. "It is more common for a bridge to have problems during renovations than before or after," he said.

I travel over two bridges to get to my office in Paramus, New Jersey, from my home on Long Island: the Throgs Neck Bridge and the George Washington Bridge. A statement like this gives me pause, since these two bridges are under constant renovation. In fact, I often wonder how long it will take to remove the copious rust from the towers of the Throgs Neck.

Still no answers
On Oct. 15, a story on the Minnesota Public Radio Web site (http://minnesota.publicradio.org/) revealed that the cause of the collapse is still unknown and probably won't be determined for many months. But organizations like the National Transportation Safety Board (NTSB) and the Minnesota Department of Transportation (MnDOT) are working hard at finding an answer.

An answer after the fact is certainly needed, no matter how long a wait. But I'm more concerned about the bridges that are still standing. I have read about inspectors who visually inspect bridges or use ultrasound techniques. Is this sufficient? Civil engineers have been building modern bridges for many years. But do they take advantage of the wealth of available electronic sensors and data-acquisition and computing equipment?

When asked at NIWeek about the bridge collapse, National Instruments CEO James Truchard pointed to his own company's products as a way to make bridges safer. In fact, case studies on NI's Web site show how some civil engineers are integrating electronics into their bridge-building work.

Monitoring structural health
One case study, entitled "Monitoring the Structural Health of the Rion-Antirion Bridge Using LabVIEW Real-Time," explains how Advitam, a division of French company Vinci Construction, developed a structural monitoring system to measure and define the behavior of the Rion-Antirion Bridge in Greece during normal operation, strong winds, and earthquakes (see the figure).

Advitam used a combination of four PXI/SCXI chassis linked with National Instruments LabVIEW Real-Time software to incorporate the conditioning, acquisition, processing, control, storage, and sharing of measurements. It also used lots of different sensors, including 3D accelerometers, strain gages, load cells, and displacement, water-level, and temperature sensors. For more, see http://sine.ni.com/cs/app/doc/p/id/cs-689.

Next question
Whether or not today's civil engineers are capable of "civiltronics" engineering, combining both disciplines to build new bridges, the fact remains that older bridges probably aren't being monitored by sensors hooked into data-acquisition systems and analyzed by computers on a day-to-day basis. Should these bridges be retrofitted? I guess you can argue that visual inspections are sufficient.

The New York Times article pointed out that the Federal Highway Administration issued a report last year that rated 13.1% of all highway bridges as "structurally deficient." It said these bridges have "deteriorated conditions of significant bridge elements and reduced load carrying capacity."

So officials know about the problems, but they don't know when they will become severe enough to cause a collapse. After all, when a bridge or any other major structure collapses, it is with brutal suddenness. Maybe an electronic system in place on a bridge could do more than indicate a need for repairs. Maybe it could actually send a warning before "bridge fall down."

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