Abstract
Scour is a significant issue for bridges worldwide that influences the global stiffness of bridge structures and hence alters the dynamic behaviour of these systems. For the first time, this article presents a new approach to detect bridge scour at shallow pad foundations, using a decentralized modal analysis approach through re-deployable accelerometers to extract modal information. A numerical model of a bridge with four simply supported spans on piers is created to test the approach. Scour is modelled as a reduction in foundation stiffness under a given pier. A passing half-car vehicle model is simulated to excite the bridge in phases of measurement to obtain segments of the mode shape using output-only modal analysis. Two points of the bridge are used to obtain modal amplitudes in each phase, which are combined to estimate the global mode shape. A damage indicator is postulated based on fitting curves to the mode shapes, using maximum likelihood, which can locate scour damage. The root mean square difference between the healthy and scoured mode shape curves exhibits an almost linear increase with increasing foundation stiffness loss under scour. Experimental tests have been carried out on a scaled model bridge to validate the approach presented in this article.
Highlights
Bridges with foundations in water can be affected by the washing away of soil, a concept termed scour erosion[1]
The experimental mode shapes derived using the concept of re-deployable accelerometers are analyzed to ascertain their performance at detecting scour-related foundation stiffness loss at the piers
While sensors were considered as being re-deployed for the purpose of the analysis in this paper, in reality this was achieved by using different sensors located at fixed points for each vehicle passage
Summary
Bridges with foundations in water can be affected by the washing away of soil, a concept termed scour erosion[1]. Indirect monitoring using passing vehicles has shown promise at detecting changes in natural frequencies[45,46,47], damping[48] and road surface roughness of bridges[49, 50] These methods rely on modal identification approaches such as Short Time Frequency Domain Decomposition (STFDD), which was used to estimate bridge mode shapes from multiple vehicle acceleration measurements in a recent study[51, 52]. The method may prove useful for rapid postflood bridge evaluation on a network
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