Evaluation of a novel video- and laser-based displacement sensor prototype for civil infrastructure applications

Abstract

Deflection measurements on structures continue to be a challenge with current sensor technologies. Material degradation and changes in the mechanical properties over time (e.g. creep and shrinkage in concrete bridges) directly impact the deflections exhibited by a structure. In this article, we introduce and discuss the evaluation of a novel laser- and video-based displacement sensor prototype to monitor displacements and rotations on structures remotely. The sensor is inexpensive, using off-the shelf components, but also accurate and practical for situations that do not allow the use of conventional displacement sensors, which require a reference base. In contrast to other image-based approaches such as digital image correlation (DIC) or Eulerian-based virtual video sensors (VVS), the digital camera of our proposed solution is located at the measurement location on the structure. The sensor was evaluated using laboratory tests to determine the practicality, accuracy, and sensitivity to lighting conditions. The accuracy of the sensor was found to be approximately ± 0.9 mm (± 0.035 in) (95% prediction limits) for a 30.5 m (100 ft) measurement distance under laboratory conditions. Finally, we applied and evaluated the sensor under real-world conditions on a concrete deck/single steel box girder pedestrian bridge under static and dynamic loading conditions as well as on a five-story steel moment-frame building under ambient conditions. Essential for field applications, the results demonstrate the prototype offers an inexpensive yet practical and accurate solution for monitoring displacements and rotations remotely.