Wavelet-based operating deflection shapes for locating scour-related stiffness losses in multi-span bridges

Scour erosion poses a significant risk to bridge safety worldwide and affects the stiffness of the soil-foundation system, resulting in global changes in the dynamic behavior of the bridges. In this paper, a new approach to detect scour at multiple locations is proposed, using wavelet-based Operating Deflection Shape (ODS) amplitudes. A numerical model of a bridge with four simply supported spans resting on piers is used to test the approach. Scour is modelled as a reduction in vertical foundation stiffness under one or multiple bridge piers. A fleet of passing trucks, modelled as half-car vehicles, are used to excite the bridge to enable structural accelerations be calculated at each support. The approach is shown to be effective with acceleration measurements at each support location in a multi-span bridge. Using a fleet of passing vehicles, the temporal accelerations measured at each support are averaged and transformed into the frequency–spatial domain, in order to estimate the wavelet-based ODS for a given scour case. A damage indicator is postulated based on differences between the ODS of healthy and scoured bridge cases. The damage indicator enables visual identification of the location of scoured piers considering a range of natural frequencies of the system.