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See Inside October 2011

Instant Health Checks for Buildings and Bridges

Sensors can detect damage that may be invisible to the naked eye



Yadid Levy/Redux Pictures

During 2011’s deadly onslaught of earthquakes, floods and tornadoes, countless buildings had to be evacuated while workers checked to make sure they were stable. The events served as a reminder that most structures are still inspected by a decidedly low-tech method: the naked eye. To speed the process and make it more accurate, investigators are researching electronic skins, evolutionary algorithms and other systems that can monitor the integrity of bridges, buildings, dams and other structures in real time.

To automatically detect tiny faults and relay their precise locations, civil engineer Simon Laflamme of the Massachusetts Institute of Technology and his colleagues are devising a “sensing skin”—flexible patches that glue to areas where cracks are likely to occur and continuously monitor them. The formation of a crack would cause a tiny movement in the concrete under a patch, causing a change in the electrical charge stored in the sensing skin, which is made of stretchable plastic mixed with titanium oxide. Every day a computer attached to a collection of patches would send out a current to measure each patch’s charge, a system that Laflamme and his colleagues detail in the Journal of Materials Chemistry.

Another engineer is applying a similar concept to bridges. To monitor deterioration inside suspension bridge cables, Raimondo Betti of Columbia University and his collaborators are testing 40 sensors in cables in New York City’s Manhattan Bridge. The sensors track temperature, humidity and corrosion rate.

Although these sensors can detect damage that occurs after they have been installed, what about damage a structure had beforehand? Roboticist Hod Lipson of Cornell University and his colleagues have developed a computer model that simulates an intact structure and runs algorithms that evolve this model until it matches data that sensors provide, which can reveal a broader scope of damage.

One concern impeding widespread applications might be that "there does not exist, yet, enough research and data that economically support continuous and timely maintenance,” La­flamme says. Another concern might be the yet to be studied long-term performance of the systems, especially in harsh environments—a matter for future research.

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