Influence of local scour at multiple piers on the vibration characteristics of a bridge under seismic excitation

Bridges founded in water can be prone to scour erosion, an effect which alters the dynamic properties of the bridge. In seismic regions, bridges are prone to excitation from earthquakes, which can be damaging to the structures. These two hazards, while independent from one another, can alter how each affects a bridge in the sense that an earthquake may pose a more serious effect on a scoured bridge than on the unscoured structure. The magnitude and location of a scour hole affecting a structure can alter the seismic bridge response to varying degrees. In this paper, a finite-element model of a multi- span bridge is created using OpenSees, and some preliminary results of a numerical investigation into scour at multiple locations and the resulting impact on the seismic behavior is reported. The bridge is subjected to ground motion considering several defined scour conditions, where scour is modelled as the incremental increase in length of a given pier. The influence of scour depth and location on the internal shear forces, displacement and accelerations of the structure are studied with a view to ascertaining critical damage combinations.