The effects of local preload on the foundation stiffness and vertical vibration of railway track

Track vibration is one of the main sources of railway rolling noise. The resilient components in the railway foundation such as the pad and ballast have significant effects on the track vibration. Usually, their parameters vary with load and frequency. The wheel load of a train causes local deformation in the track and the foundation, so the railpads and the ballast are preloaded and thus their stiffness has different values at the supports near the wheel load from the other supports. In this paper the preloads in the pad and ballast caused by a single wheel load are studied by considering the non-linear properties of the track foundation, and thus the preloaded pad and ballast stiffnesses are determined. A model of the track dynamics based on an infinite discretely supported Timoshenko beam with preloaded pad and ballast dynamic stiffnesses is developed. Its vertical vibration behaviour under the influence of the local wheel load is investigated. It is shown that the point receptance for vertical vibration is strongly affected by the local wheel load at low frequencies, but the effect of the local wheel load on the average wave propagation decay rate along the rail is very limited. (C) 1999 Academic Press.