Sag-based cable tension force evaluation of cable-stayed bridges using multiple digital images

•Digital images were used to evaluate the cable tension force of cable-stayed bridges.•Cable tension evaluation method is based on digital image processing and parabolic cable theory.•Cable tension results measured from Digital images were verified in comparison with measured lift-off test data. Cable tension is a critical variable for evaluating the structural health and safety of cable-stayed bridges. Although various vision-based systems have been developed for measuring the tension of cables, it is still cumbersome to measure the instantaneous tension of cables, which fluctuates owing to external loadings such as temperature and wind. Therefore, in this paper, a method for evaluating the tension and range of tension using multiple digital images is proposed. A field test was conducted on cables of a real cable-stayed bridge to confirm the applicability and reliability of the proposed method. The cable tension evaluated using the image was compared with the value measured directly through lift-off tests, and the tension evaluated was consistent with that measured directly. The proposed method can provide a time- and cost-effective option for determining the instantaneous cable tension force of cable-stayed bridges compared to existing tension measurement systems.