Magnifying vibrations in bridges and buildings

To the naked eye, buildings and bridges appear fixed in place, unmoved by forces like wind and rain. But in fact, these large structures do experience imperceptibly small vibrations that, depending on their frequency, may indicate instability or structural damage.

CSAIL researchers have now developed a technique to “see” vibrations that would otherwise be invisible to the naked eye, combining high-speed video with computer vision techniques.

Normally, high-speed video wouldn’t pick up such subtle vibrations from a building. To do this, the researchers employed a computer vision technique called “motion magnification” to break down high-speed frames into certain frequencies, essentially exaggerating tiny, subpixel motions.

In laboratory experiments, the researchers were able to detect tiny vibrations in a steel beam and a PVC pipe. The vibrations measured by the technique matched those picked up by accelerometers and laser vibrometry — precise but expensive techniques commonly used in infrastructure monitoring.



Oral Buyukozturk, a professor of civil and environmental engineering at MIT, says motion magnification provides a faster, cheaper, and noninvasive alternative to existing monitoring techniques.

“This could be a noncontact sensor technology that can be used for economic and speedy applications,” Buyukozturk says. “Depending on your objective, perhaps you could use the camera on your cellphone for screening, and if you detect something, you could concentrate on it with a high-power camera. There are levels of inspection, and you don’t always have to start with the highest-quality camera.”

Buyukozturk has co-authored a paper, along with lead author and graduate student Justin Chen, which appears in the Journal of Sound and Vibration. The paper’s other co-authors are CSAIL graduate student Neal Wadhwa and postdoc Young-Jin Cha, along with CSAIL principal investigators Fredo Durand and William Freeman.

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