Scour Depth Determination of Bridge Piers Based on Time-Varying Modal Parameters: Application to Hangzhou Bay Bridge

Scour of bridge piers has been demonstrated to be one of the most common causes of bridge instability and destruction. This article presents a long-term approach to scour depth determination for a cable-stayed bridge based on time-varying modal parameters generated from a structural health monitoring system. The finite-element model, updated according to dynamic testing before opening the bridge to traffic, was employed to identify the sensitive modes for scour depth variation and establish the numerical relationship between scour depth and the modal parameters. Afterward, the time-varying modal parameters were determined using monitored acceleration data sets. Numerical investigation has indicated that these modal parameters are also significantly impacted by environmental conditions, which will cause confusion when determining scour depth. Nonlinear principal component analysis (NLPCA) was chosen to separate the environmental influence from the scour depth influence on modal parameters. Finally, comparison of the scour depth determined based on modal parameters with the results of visual inspection by divers exhibits the effectiveness of the proposed approach. Moreover, this study could provide guidelines for future decision making regarding the early warning and maintenance of bridge piers.