Identification of Bridge Scour Depth by Tracing Dynamic Behaviors of Superstructures

A methodology to identify and analyze the bridge scour depth by tracing the dynamic behaviors of superstructures was developed. This proposed methodology basically relies upon the bridge scour-induced effects on the variations of two dynamic features of superstructures, i.e., the natural frequency of vibration and mode of vibration. Firstly a flexibility matrix incorporating the two dynamic features is deduced for bridges under scour conditions. Then, using the scour-induced variations of such flexibility matrix, a new parameter of “[D]-based deflection change” Δδ is defined as an important index for identifying the scour depth. Such an index Δδ is determined by both FEM (Finite Element Method) simulations and on-site measurements on the dynamic features of superstructures. By doing this, the scour depths corresponding to the measured Δδ are back-deduced based on a pre-simulated relationship between Δδ and scour depths. A case study based on the simulation and a demonstration based on actual field data are finally given to demonstrate the application procedure and qualitatively verify the feasibility of the proposed methodology. This methodology does not require any continuous and long-term bridge monitoring using underwater instrumentations and could be conveniently integrated to a routine assessment or structural monitoring system.