Dynamic characteristics of suspension bridge hanger cables using digital image processing

In this study, a non-contact measurement method is proposed to estimate the tension in hanger cables by using digital image processing. Digital images were acquired through a vision-based system using a portable digital video camera (camcorder), which was used to remotely measure the dynamic responses and was chosen because it is convenient and cost-efficient. Digital image correlation technique, as one of digital image processing algorithms, was applied to develop an image processing algorithm. An image transform function was used to correct the geometric distortion between the deformed and undeformed images and to calculate the subpixels. The motion of the vision-based system caused by external wind or vibration at camera location was corrected considering a fixed object in the image without any additional sensors. Using this algorithm, the dynamic response of the hanger cable and the resolution of the modal frequencies were improved. It was also confirmed that the dynamic characteristics of the hanger cables can be estimated with only the cable shape not attaching any target.