A Contribution to the Material Behaviour of Ballast on Railway Bridges

Railway bridges are subjected to intensive dynamic stresses due to train crossings.
The resulting system response (accelerations) is estimated in advance through
dynamic calculations. The basis of the calculations is the knowledge of the natural
frequencies. Various studies have shown that a discrepancy between the measured and
the numerical determination of these natural frequencies often occurs for short frame
bridges. In common practice, the ballast is assumed to be non-supporting regarding
the global structural stiffness. In some cases, rheological models of vertical springs
and dashpots are used to consider the load distribution in vertical direction.
This publication discusses ballast stiffness on the material level. This leads to a
stiffness contribution of the ballast to the horizontal stiffness (fraction of bending
stiffness) and thus to a stiffening of the structure. It is shown that ballast can be defined
in terms of stress and shear strain dependence. If ballast stresses and expected
superstructure accelerations are known, an equivalent ballast stiffness can be
determined and taken into account in a dynamic calculation using a linear approach. ... mehr
The material approach is verified by a scaled component test and a parallel numerical
reference calculation.