Estimating tension of a prestressed concrete cable-stayed bridge under construction and traffic use conditions using a vision-based system

In cable-stayed bridges, cable is the primary member supporting the load, so cable tension is a very important factor in evaluating the integrity and safety of this type of bridge. The direct method of measuring the force of a cable using a load cell or hydraulic jack, and the indirect method of calculating the tension inversely using the shape condition of the cable and the measured dynamic characteristics are the most frequently used methods of measuring cable tension. In this study, cable tension was estimated using the indirect method. A vision-based system was also applied as a sensor to measure the cable's dynamic response. In order to improve the recognition of the control point during image analysis, the helical fillet of the cable was distinguished from the cable using mathematical morphology. A distorted image including a vehicle shows inaccurate results in image analysis due to the installation position of the vision-based system. Accordingly, the image including the vehicle was removed by calculating the similarity between the two images. In the cable-stayed bridge under construction, the tension measured in the lift-off test and the tension estimated by applying the vibration method showed an error of less than 3 %. The accuracy of the tension estimated using the vision-based system could be confirmed. In addition, when the tension measured in the existing cable-stayed bridge was compared with the tension measured during construction, the tension of the cable was confirmed to be well-maintained even after about 10 years of use.