A new method is proposed for measuring interstory drift, the shifting of floors relative to one another when a building undergoes wind or earthquake loading. A laser crosshair is projected from one story to the next, and onto a set of photodetectors which sense changes in the position of the projected light. This paper reports the theory of operation and a quasi-static verification of the method using micropositioning stages to provide input displacements. Lateral positions, including translational and rotational components are calculated from the photodetector outputs, and show excellent agreement with input displacements. The overall performance of the sensor system is extremely linear and predictable, and appears robust enough for field deployment.
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