Temperature dependence of ballast stiffness on a railway bridge

In this study it is demonstrated that ballasted bridges can exhibit a step-like variation on the eigenfrequencies as the temperature varies. This change manifests as an important increase in the eigenfrequencies as temperature drop below 0 °C. The reason for this phenomenon is unknown but it is theorized that it is due to frozen water acting as a bonding agent between the ballast particles, increasing the stiffness of the ballast layer and thus the eigenfrequencies of the bridge. The step-like nature of the change and the fact that it occurs at around 0 °C seem to point in this direction. A Finite Element model of the bridge was developed to explore what elasticity modulus for the ballast would lead to an increment of the eigenfrequencies that matches the observed one.