Vision-Based Monitoring of Post-Tensioned Diagonals on Miter Lock Gate

Miter gates are structures that act as both the damming surface and doorway of lock chambers and are commonly found on American rivers. Miter gates are assumed to have very little torsional stiffness, and their geometry causes the gate to twist under its own weight. Thus, long, slender, post-tensioned steel members (termed diagonals) are attached across the diagonal dimensions of the miter gate to provide torsional stiffness and counteract the twist of the gate. Maintaining an appropriate level of tension in these diagonals is of critical importance to both the structural performance and serviceability of the miter gate. Traditional contact sensors to monitor tension in diagonals are economically impractical. This study investigates a noncontact method for monitoring the tension by means of the Lucas-Kanade approach to optical-flow on videos of vibrating diagonals to extract a time history of displacement. From the displacement, the dominant frequencies of vibration of the diagonal members are estimated and used to determine the tension in the diagonals using a beam theory. The proposed approach is particularly attractive because diagonals will be monitored periodically, rather than continuously. Moreover, the vision-based method is simplified by using a human-in-the-loop approach, whereby features to be tracked via optical flow are manually selected by a user. The efficacy of the approach is demonstrated by means of a scale-model lab experiment of miter gate diagonals, and the effects of camera orientation, vibration amplitude, and camera distance are investigated. The results show that, with appropriate modeling of the behavior of the diagonals, the vision-based method is a viable approach to determine the tension in miter gate diagonals.