Automatic assessment of the fatigue life of cables of cable‐stayed bridges by on‐line monitoring

To accurately and timely evaluate the long‐term performance of cables in cable‐stayed bridges, an automatic perception technology scheme by on‐line monitoring of cable vibrations is proposed for the fatigue damage evaluation of in‐service cables. In the fatigue‐stress amplitude of cables, the stress produced by tension changes caused by external actions like traffic, wind, and temperature is the main component. When cables vibrate significantly, the stress caused by changes in cable vibration‐induced additional stress should not be neglected. Besides axial stress, bending stress is also significant in cable fatigue damage analysis. To make cable fatigue life prediction closer to real engineering scenarios, this factor should be considered. First, based on the cable dynamic stiffness theory, a method is proposed for the automatic gathering of the actual full‐stress time history of a cable by on‐line vibration monitoring. Furthermore, based on Miner's linear fatigue damage accumulation theory, an automatic fatigue life assessment method is proposed and applied to the vibration monitoring data of cables on an operational bridge. The results indicate that the proposed technology realizes automatic on‐line monitoring of cable forces and fatigue assessment of cables. Through statistical analysis of cable fatigue stress amplitude, it was determined that in cable‐stayed bridges, compared to long cables, short cables are more sensitive to external variable loads, typically experiencing larger and more frequent tension changes, and are more prone to fatigue. Therefore, short cables should be given more attention when analyzing cable fatigue in cable‐stayed bridges.