Abstract
Recent tragedies around the world have shown how accidents in the cable-stayed bridges can wreak havoc on the society. To ensure the safety of the cable-stayed bridges, several studies have estimated the cable tension force using the vibration of cables. Most of these methods for estimating the tension of a cable start with measuring the displacement of the cable. Recent development of commercial cameras provide opportunity for more convenient and efficient method for measuring the displacement of cable. However, traditional vision-based displacement measurement methods require the assumption that the movement of the cable should be measured in parallel to the camera plane. This assumption limits the installation location of the camera when measuring the displacement of a cable. Therefore, this study introduces a new vision-based cable displacement measurement system that can measure the displacement of a cable in various locations even when the camera is installed in the side of the cable. The proposed method consists of three phases: (1) camera projection matrix estimation, (2) cable tracking in the image coordinate, and (3) cable displacement estimation in the world coordinate. To validate the performance of the proposed method, a simulation-based validation test, a lab-scale validation test, and an on-site validation test were conducted. The simulation-based validation test verified the performance of the proposed method in an ideal condition, and the lab-scale validation test showed the performance of the method in physical environment. Finally, the on-site validation test showed that the proposed method can measure the cable displacement with a side view camera.
Highlights
Recent tragedies around the world showed how accidents in the cable-stayed bridges can wreak havoc on the society
Kim et al estimated cable tension forces based on the natural frequency of cables [4], and Yin et al analyzed the cable tension force using the response of a vehicle passing on a cable-stayed bridge [5]
This paper presented a new method for estimating the displacement of a cable from a side view camera
Summary
Recent tragedies around the world showed how accidents in the cable-stayed bridges can wreak havoc on the society. Zhao et al used microwave intrametric radar to measure the displacement of the Nanjing Eye cable-stayed bridge and estimate the tension force [8]. Most of these studies required the measurement of cable displacement either directly or indirectly. The camera should be relocated to the side of the cable to secure the line of sight, but the measured displacement using the video recorded from the side view will contain a large projection error. The system is comprised of three phases: estimating the camera projection matrix, tracking the cable in the image coordinate, and restoring the displacement into 3D world coordinate. In phase 3, the cable displacement in the world coordinate is restored by combining the results from phase 1 (i.e., camera projection matrix) and phase 2 (i.e., location of the target in 2D image coordinate)
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