Because of the characteristics of cable-supported bridges, the cable tensile force is considered a critical item in their maintenance. In particular, because the evaluation of the cable tensile force in a cable-stayed bridge is essential for understanding the general status of the structural system, identifying the initial values of this force in the construction of a bridge and then accurately predicting and comparing its estimated values during traffic use are very important tasks for the maintenance of a cable-stayed bridge. Therefore, in this study, a vision-based monitoring system that utilizes an image processing technique was developed to estimate the tensile force of stay cables during traffic use. A remotely controllable pan-tilt drive was installed in the developed vision-based monitoring system to estimate the forces on multiple cables using a single system. The use of a 20× electric zoom lens made it possible to achieve sufficient resolution to remotely derive the dynamic characteristics of the stay cables.

In this study, a method to measure multi-point displacement responses by using a digital image processing technique is suggested. Digital images are acquired by a commercial digital camcorder, which is the sensor to measure remote displacement responses considering convenient and economical aspects for use. The digital image correlation (DIC) as one of digital image processing techniques is applied to the algorithm developed and the image transform function (ITF) to correct the movements and errors between the image without deformation and that with deformation is also used to increase the resolution of displacement responses. One shaking table test and several field tests to validate this algorithm, which can measure multi-point displacement responses of structures by using digital image processing techniques, were carried out