Scour evaluation for foundation of a cable-stayed bridge based on ambient vibration measurements of superstructure

Abstract This study develops a foundation scour evaluation method merely using the ambient vibration measurements taken from the superstructure of a cable-stayed bridge. Various modal frequencies of girder and those of the local pier are first identified for Kao-Ping-Hsi Bridge. The finite element model of this bridge is then constructed to perform the modal analysis with original design parameters. Combining the above results, this work further determines the best boundary support conditions for the model to fit the identified modal frequencies of bridge girder. According to this globally best fitted model, the optimal soil stiffness is first decided by fitting the critical bridge frequencies with a known deposit height at the pylon. Subsequently, the scour depth at a pier can be estimated by varying the depth of its supporting soil to fit the two sensitive frequencies of local pier modes. Finally, a direct measurement scheme is carried out to verify the estimated scour depth.