Vibration-Based Identification for the Presence of Scouring of Cable-Stayed Bridges

Abstract

This study applies structural dynamics monitoring to identify the presence of bridge scouring through tracing the changes of vibration characteristics induced by scour. Four scour-indicating dynamic features, i.e., the frequency change ratio, modal assurance criterion, mode shape curvature, and flexibility-based deflection, are applied as the scour indicators. Based upon the study of a cable-stayed bridge, each scour indicator is calculated and its corresponding relationship with scour depth is obtained. The feasibilities and effects of using each indicator ae comprehensively examined. After comparison, the flexibility-based deflection is finally recommended as a sensitive and practical indicator to identify the presence of the scouring. When applied in practice, the deflection can first be extracted from the ambient vibration measurement; then the scour depth can be back-deduced based on the preobtained relationship between the deflection and scour depth. For the specific cable-stayed bridge investigated in this study, the pylon-based deflection indicator can identify the scour presence more effectively and distinguishably. The scour location can also be known because the scoured pylon or pier shows many obvious deflection changes compared with those without scour effects. This study demonstrates that tracing the change of vibration responses can both qualitatively and quantitatively identify the scour of cable-stayed bridges. This vibration-based technique does not require any underwater devices or operations, which could be integrated into a routine assessment task for bridges.