EN 13146-9: Railway Applications – Test Methods for Fastening Systems – Part 9: Determination of Stiffness

What is EN 13146-9?

EN 13146-9 is a technical standard titled “Railway applications – Track – Test methods for fastening systems – Part 9: Determination of dynamic stiffness.” It is a fundamental part of the EN 13146 series, focusing on the “elasticity” of the connection between the rail and the Sleeper.

In modern Infrastructure Management, the track is no longer seen as a rigid structure but as an elastic system. The stiffness determined by this standard affects how Rolling Stock loads are “spread” across multiple sleepers. If a fastening system is too stiff, it can lead to rapid degradation of the Ballast; if it is too soft, it may compromise Track Geometry and Operational Safety.

Static vs. Dynamic Stiffness

The standard provides distinct methodologies for measuring how the fastening system reacts under different loading conditions:

• Static Stiffness ($k_{stat}$): Measured under slow-moving or stationary loads. This is used to calculate the general deflection of the rail under the weight of the train.
• Dynamic Stiffness ($k_{dyn}$): Measured at higher frequencies (typically between 5 Hz and 30 Hz for track stability, and higher for noise studies). This simulates the vibration and impact forces generated by a train moving at speed.
• The Low-Frequency vs. High-Frequency Range: EN 13146-9 defines specific frequency ranges to ensure that the material’s damping properties are correctly accounted for, which is essential for Vibration Mitigation in urban areas.

Test Procedure and Setup

To ensure Technical Delivery Conditions are met, the test follows a rigorous lab protocol:

• Assembly: A complete fastening assembly (including rail pad, clips, and baseplate) is mounted on a concrete block or sleeper section.
• Cyclic Loading: A hydraulic actuator applies a vertical load that oscillates between a defined minimum and maximum value, mimicking the passage of wheelsets.
• Measurement: High-precision displacement transducers measure the “compression” of the rail pad down to fractions of a millimeter.

Relevance to the Track-Train Interface

The data derived from EN 13146-9 is used by engineers to:

• Protect Infrastructure: Optimized stiffness reduces the “impact” on sleepers and ballast, extending Maintenance Intervals.
• Environmental Protection: By selecting pads with specific dynamic stiffness, railways can reduce ground-borne noise and vibrations in residential zones.
• Rolling Stock Safety: Ensuring the rail stays within the elastic limits to prevent fatigue in the Wheel-Rail Interface.

Summary of Stiffness Impact