Sensor for Measuring Interstory Drift Could Aid in Earthquake Response

A new optical sensor developed by scientists and engineers at Lawrence Berkeley National Laboratory (Berkeley Lab), Lawrence Livermore National Laboratory, and the University of Nevada-Reno could reduce the time needed to reliably evaluate whether critical buildings, such as hospitals and schools, are safe to reoccupy after an earthquake. The Discrete Diode Position Sensor (DDPS) uses a laser source and a position-sensitive detector to measure interstory drift within buildings quickly and accurately.

A new sensor developed at Lawrence Berkeley National Laboratory combines laser beams with a position-sensitive detector to directly measure drift between building stories, an essential part of assessing earthquake damages in buildings and deeming them safe to reoccupy. Courtesy of Diana Swantek/Berkeley Lab.

To directly measure structural drift, a laser light is projected across a story height to sense the position at which the light strikes a detector located on the adjacent building floor. Using a geometric array of small, inexpensive photodiodes, the sensor is able to instantly track the position of an impinging laser beam.

So far, DDPS has held up to three rounds of stringent experimental shake table testing. “The rigorous testing the DDPS has undergone indicates how the drift displacements measured on the three testbeds compared to representative drifts that could be achieved on an actual full-scale building undergoing strong shaking from an earthquake,” professor David McCallen said.

DDPS is a small device that will be positioned between building stories to detect interstory drift and transmit data about building damages to response planners. Its debut comes as governments at every level make post-earthquake building inspection and reoccupation a central focus of response planning, and as the highly anticipated next generation of remote connectivity, 5G, becomes reality. Courtesy of Diana Swantek/Berkeley Lab.

The new generation of the DDPS is a quarter of the size of the team’s original sensor design, which it began to work on in 2015. The new DDPS features 92 diodes staggered in a rectangular array so that the laser beam is always on one or more diodes. The new sensor is being deployed initially in a multistory building at Berkeley Lab, which is adjacent to the Hayward Fault, considered one of the most dangerous faults in the United States.

“Until now, there’s been no way to accurately and directly measure drift between building stories, which is a key parameter for assessing earthquake demand in a building,” McCallen said. The ability to measure and display key interstory drift information immediately after an earthquake could provide critical data for making informed decisions on building occupancy and the potential to maintain functional use of facilities after a quake occurs.