Estimation of Bridge Pier Natural Frequency for Scour Monitoring Using the Random Decrement Technique

Scour poses a critical problem in bridge engineering, leading to a decrease in the stiffness and stability of bridge foundations. During a flood, the risk of bridge scouring is particularly high, while the detection can be difficult. Aside from the conventional depth-measuring methods, the applications of structural modal information to bridge scour detection have attracted increasing attention. In this paper, a framework for long-term estimation of the natural frequency of a bridge pier is developed. The Random Decrement technique is used to calculate a free decay response from the accelerations measured from a railway bridge pier. By adjusting computation parameters, reliable frequency estimation is achieved using the Eigensystem Realization Algorithm and Fourier transform. A power spectral density ratio of the accelerations is further employed to distinguish the target mode, thereby enhancing the estimation consistency. The identified natural frequencies align well with impact test results, and the changes in the frequencies over an extended period have been tracked.