Conventional sensors, such as the accelerometers and velocimeters, are commonly applied to estimate the vibration of stay cables for the recognition of dynamic response. Such practice is relatively time-consuming and expensive due to the challenge from considerable amount of cabling work and installation of data acquisition logger. Two measurement methods based on digital image techniques, digital image processing (DIP) and digital image correlation (DIC), are adopted in this study to identify the cable force with capturing single and multiple points images by camera. To verify the reliability of the methods, the results are compared with accelerometer, and the relative deviations between the two methods and the accelerometers are within 5%. The multi-point vibration mode of stay cable using the digital image techniques was compared to numerical simulation for exploring the role of mode difference in cable force measurement. Experimental results show that the application of the digital image techniques in stay cable bridge is sustainable and advantageous and the differences between various digital image techniques are shown clearly.
