Estimation of Dynamic Characteristics of Long-span Bridge Cables Using Image Signal Processing

As to the long-span bridges, the health monitoring of a bridge can be identified by measuring tension force on cable repeatedly. The tension force on cable is measured either by direct measurement of stress of cable using load cell or hydraulic jack, or by vibration method estimating tension force using cable shape and measured dynamic characteristics. In this study, image signal processing was used to estimate the tension force of the remote cable using vibration method. A portable digital camcorder was used as a vision-based system in consideration of user convenience and economic feasibility. A digital image correlation (DIC) technique as one of digital image processing algorithm is applied to develop the image processing algorithm. The image transform function (ITF) was used to correct the geometric distortion between the deformed and undeformed images, and to calculate the subpixel. The motion of the vision-based system was corrected using a fixed object in the image, without installing an additional sensor, the resolution of dynamic responses and modal frequencies were improved.