Methods for Measuring the Dynamic Stiffness of Resilient Rail Fastenings for Low Frequency Vibration Isolation of Railways, Their Problems and Possible Solutions

SUMMARY Low frequency ground or structure-borne sound and vibration emission from urban rail transport systems can be greatly reduced by reducing the stiffness of the rail fastening. Estimates and models of the efficacy of such systems require accurate measurements of their dynamic stiffness over the frequency range of interest, and European Standards make recommendations for such measurements. This paper describes these methods and their shortcomings when applied to modern complete assemblies with low stiffness, one problem of which is the contribution of inertial forces at frequencies approaching and above the natural resonance of the system. This paper suggests a method for correcting for this inertial force, and tests this correction with the driving point method of dynamic stiffness measurement when applied to the Pandrol VANGUARD resilient rail fastening. The preliminary tests effectively triple the frequency range of valid measurements, a result which could be improved when applied to stiffer systems or with further improvements to the test equipment.