TY - JOUR
T1 - Structural Displacement Measurement Using an Unmanned Aerial System
AU - Yoon, Hyungchul
AU - Shin, Jaeho
AU - Spencer, Billie F.
N1 - Funding Information:
The authors gratefully acknowledge the funding from the Association of American Railroads (AAR) for this research, as well as the strong support from Richard Joy. Collection of the displacements of the railroad bridge in Rockford, Illinois part of research funded by the Federal Railroad Administration (FRA, Cameron Stuart, Program Manager). The efforts of Sandro Scola and James Tuchscherer from CN and Do Soo Moon, Fernando Gomez, Jongwoong Park, and Tim Prunkard from the University of Illinois in collecting this data are also appreciated very much.
Publisher Copyright:
© 2017 Computer-Aided Civil and Infrastructure Engineering
PY - 2018/3
Y1 - 2018/3
N2 - Vibration-based Structural Health Monitoring (SHM) is one of the most popular solutions to assess the safety of civil infrastructure. SHM applications all begin with measuring the dynamic response of structures, but displacement measurement has been limited by the difficulty in requiring a fixed reference point, high cost, and/or low accuracy. Recently, researchers have conducted studies on vision-based structural health monitoring, which provides noncontact and efficient measurement. However, these approaches have been limited to stationary cameras, which have the challenge of finding a location to deploy the cameras with appropriate line-of-sight, especially to monitor critical civil infrastructures such as bridges. The Unmanned Aerial System (UAS) can potentially overcome the limitation of finding optimal locations to deploy the camera, but existing vision-based displacement measurement methods rely on the assumption that the camera is stationary. The displacements obtained by such methods will be a relative displacement of a structure to the camera motion, not an absolute displacement. Therefore, this article presents a framework to achieve absolute displacement of a structure from a video taken from an UAS using the following phased approach. First, a target-free method is implemented to extract the relative structural displacement from the video. Next, the 6 degree-of-freedom camera motion (three translations and three rotations) is estimated by tracking the background feature points. Finally, the absolute structural displacement is recovered by combining the relative structural displacement and the camera motion. The performance of the proposed system has been validated in the laboratory using a commercial UAS. Displacement of a pinned-connected railroad truss bridge in Rockford, IL subjected to revenue-service traffic loading was reproduced on a hydraulic simulator, while the UAS was flown from a distance of 4.6 m (simulating the track clearance required by the Federal Railroad Administration), resulting in estimated displacements with an RMS error of 2.14 mm.
AB - Vibration-based Structural Health Monitoring (SHM) is one of the most popular solutions to assess the safety of civil infrastructure. SHM applications all begin with measuring the dynamic response of structures, but displacement measurement has been limited by the difficulty in requiring a fixed reference point, high cost, and/or low accuracy. Recently, researchers have conducted studies on vision-based structural health monitoring, which provides noncontact and efficient measurement. However, these approaches have been limited to stationary cameras, which have the challenge of finding a location to deploy the cameras with appropriate line-of-sight, especially to monitor critical civil infrastructures such as bridges. The Unmanned Aerial System (UAS) can potentially overcome the limitation of finding optimal locations to deploy the camera, but existing vision-based displacement measurement methods rely on the assumption that the camera is stationary. The displacements obtained by such methods will be a relative displacement of a structure to the camera motion, not an absolute displacement. Therefore, this article presents a framework to achieve absolute displacement of a structure from a video taken from an UAS using the following phased approach. First, a target-free method is implemented to extract the relative structural displacement from the video. Next, the 6 degree-of-freedom camera motion (three translations and three rotations) is estimated by tracking the background feature points. Finally, the absolute structural displacement is recovered by combining the relative structural displacement and the camera motion. The performance of the proposed system has been validated in the laboratory using a commercial UAS. Displacement of a pinned-connected railroad truss bridge in Rockford, IL subjected to revenue-service traffic loading was reproduced on a hydraulic simulator, while the UAS was flown from a distance of 4.6 m (simulating the track clearance required by the Federal Railroad Administration), resulting in estimated displacements with an RMS error of 2.14 mm.
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U2 - 10.1111/mice.12338
DO - 10.1111/mice.12338
M3 - Article
AN - SCOPUS:85041930429
SN - 1093-9687
VL - 33
SP - 183
EP - 192
JO - Computer-Aided Civil and Infrastructure Engineering
JF - Computer-Aided Civil and Infrastructure Engineering
IS - 3
ER -