Optical sensor tech evaluates earthquake building damage

July 15, 2019 //By Rich Pell
Optical sensor tech evaluates earthquake building damage
Scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) say they have developed a new optical sensor that could speed up the time it takes to evaluate whether buildings are safe to occupy shortly after a major earthquake.

The technology - called the Discrete Diode Position Sensor (DDPS) - autonomously captures and transmits data depicting the relative displacement between two adjacent stories of a shaking building. As a result, say the researchers, it is able to provide reliable information about building damage immediately following an earthquake, and could expedite efforts to safely assess, repair, and reoccupy buildings post-quake.

"Until now, there's been no way to accurately and directly measure drift between building stories, which is a key parameter for assessing earthquake damage in a building," says David McCallen, a senior scientist in the Energy Geosciences Division at Berkeley Lab and faculty member at the University of Nevada. "We are excited that this sensor technology is now ready for field trials, at a time when post-earthquake response strategies have evolved to prioritize safe, continued building functionality and re-occupancy in addition to 'life safety.'"

Traditionally, to measure building interstory drift, engineers mounted strong motion earthquake accelerometers at select elevations to secure data on the back-and-forth and side-to-side force imposed on a shaking building. But processing the acceleration data from these instruments to obtain building drift displacements is very challenging, say the researchers, due to the frequency limitations of the sensors, especially when buildings have sustained permanent displacements associated with damage.

In addition, they say, receiving the data quickly enough to inform decision-making on continuity of operations and occupant safety is even more difficult. Also, because typical building accelerometer-based instrumentation can be quite costly, systems tend to be very sparse with accelerometers on relatively few buildings.

As an alternative, the DDPS leverages laser beams with optical sensors to directly measure building interstory drift. It is based on projecting laser light across a story height to sense the position at which the light strikes a detector located on the adjacent building floor to directly measure structural drift.

The tool developed at Berkeley Lab relies on using a laser source and position sensitive

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