Keywords: railways, vibration, elastomer, constitutive model, dynamic test.

Vibrations induced by train passage can arouse annoyance to nearby neighbours that stem from rumbling sounds and perceptible movements. One of the most common solutions to avoid vibration disturbance to inhabitants residing close to a railway system is to install mitigation elements, usually made of elastomeric materials, in the track superstructure. Given their elasticity, they are able to deform under compression loads and thus, dissipate vibration energy, reducing the vibration level transmitted to the ground and hence, to the adjoining dwellings.

The efficiency of the attenuation solution is usually evaluated through its insertion loss curve, which represents the ratio between vibration transmitted with and without the mitigation device. However, this curve is frequently obtained using simple models not accounting for real elastomeric behaviour. In order to propose a more accurate model to represent track elastomeric components, a review of the most characterising properties of elastomeric stress-strain behaviour and the existing models employed to represent such properties is undertaken.

As affirmed by Thompson [1] and Castellani et al. [2], the damping of the vibration induced by railroad traffic is frequency dependent, and hence, the viscous effect cannot be neglected. Using a mixed model combining hysteretic and viscoelastic damping, similar to the one proposed Ribeiro [3], elastomeric behaviour can be accurately predicted, while keeping the model in the linear field. Assuming this constitutive law, a new model to calculate the insertion loss of an isolated track is presented in this paper.

The vibration attenuation of isolator devices depends strongly on the dynamic stiffness and damping ratio, both obtained from the dynamic test. The finite element modelling of this test is proposed with the aim of improve existing solutions.

1

D. Thompson, "Track Vibration", in "Railway Noise and Vibration. Mechanisms, Modelling and Means of Control", Elsevier, Amsterdam, 29-51, 2009.

2

A. Castellani, G. Kajon, P. Panzeri, P. Pezzoli, "Elastomeric Materials Used for Vibration Isolation of Railway Lines", Journal of Engineering Mechanics, 124(6), June 1998. doi:10.1061/(ASCE)0733-9399(1998)124:6(614)

3

A.M.R. Ribeiro, N.M.M. Maia, M. Fontul, J.M.M. Silva, "Complete Response of an SDOF System With Mixed Damping Model", Universidade Técnica de Lisboa, 2007.

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