Dynamic Stiffness of a RockDelta vibration isolation solution measured according to ISO 10846-2. The two curves represent two different static load conditions.
Vibration Mitigation Prediction of a Resiliently Supported Track
Prediction of vibration isolation efficiencies (Insertion Loss) in a track system is obviously an important issue. Under ideal conditions, vibration attenuation up to more than 25 dB can be achieved.
The vibration isolation efficiency can only be assessed in the context of specific project conditions. Vibration isolation prediction is performed based upon known project parameters, including:
- Complex Modulus and masses of the track construction elements
- Unsprung mass of the bogie
- Complex Modulus of the ground
- Complex Modulus of the vibration isolation
The most important characteristic for vibration isolation of railway tracks is the Dynamic Stiffness of the chosen resilient element measured according to ISO 10846-2: Acoustics and Vibration – Laboratory Measurements of Vibro-Acoustic Transfer Properties of Resilient Elements. The Loss Factor of the resilient material may be determined from the imaginary and real part of the Dynamic Stiffness as described in ISO 10846-2.
The Dynamic Stiffness and Loss Factor may be used as inputs to predict the vibration attenuation in both simple one-dimensional models and more advanced three-dimensional models such as Boundary Element Methods or Finite Element Methods.
The Importance of Constant Material Parameters
When it comes to the accuracy of a vibration isolation prediction of performance constant material parameters of the resilient element are obviously of paramount importance.
Large and unexpected changes over time or between different productions batches, for instance in Dynamic Stiffness, may render a vibration isolation prediction useless or it may cause higher rail deflections than anticipated during the design of the track. Furthermore, unexpected changes in the Dynamic Stiffness may alter the resonance frequency (or frequencies) of the track system thereby possibly bringing dynamic forces, e.g. related to the sleeper passing frequency, into the region of this resonance frequency.
Related to the importance of having constant and known material parameters throughout the lifetime of a track resilient element, it is worth noticing that the Dynamic Stiffness of RockDelta stone wool – as proved for instance during exhaustive fatigue resistance tests with repeated load cycles up to an amazing 100 million – has shown virtually no difference between new and load-cycled material.
Combining this unique fatigue resistance with the ultra-low sensitivity to climatic factors, track anti-vibration solutions from the RockBallast® and RockXolid® product lines have shown to ensure predicted levels of vibration isolation for decades.
