Elastomeric materials used for vibration isolation of railway lines

To attenuate disturbance in residential buildings located along metropolitan railway lines, special types of track bedding have been designed, based on fixation of the rail on floating slabs, resting on elastomeric materials. Laboratory tests on small elastomeric pads show that the energy dissipation, under cyclic loading of constant amplitude, can be suitably represented by a combination of a viscous and an hysteretic damping, A. significant strain-rate sensitivity is evident. As a first approximation, the stiffness has been represented as an increasing function of frequency, characterized by an asymptotic value. The frequency range of 0-100 Hz has been investigated. Eight types of elastomeric materials have been tested. Comparison shows that the stiffness increases with the increase of the material density. The analytical model has been checked in two different experiences. (1) A prototype of a floating slab track, 14.8 m long, has been assembled in the laboratory and tested under fixed amplitude and harmonic loads. While the experiments on small pads were restricted to uniform loading conditions, the track prototype was excited by a concentrated load, thus inducing different deformations along the specimen, decreasing with the increase of the distance from the point of loading. (2) An experimental track, 100 m long, made up of the same set of elements of the prototype, has been inserted in a railway line. A series of vibration records has been collected during train passages. Comparisons between measured and computed vibrations were used to provide a specific notion of the relevance in a practical problem of the analytical assumptions. Errors in the evaluation of the peak displacement and of the root-mean-square value are limited to a few percent.