Holding the Line: EN 13146-1 Rail Restraint Testing

Introduction to EN 13146-1

In modern railway tracks, particularly those using Continuous Welded Rail (CWR), the rail acts like a giant thermometer, wanting to expand in summer and shrink in winter. EN 13146-1, titled “Railway applications – Track – Test methods for fastening systems – Part 1: Determination of longitudinal rail restraint,” defines the laboratory procedure to verify that the fastening system grips the rail tightly enough to prevent this movement.

This test measures the “slip resistance” of the fastener. If this restraint is too low, the rail will slide through the clips (Rail Creep), leading to dangerous gap openings in winter or track buckling in summer.

Snippet Definition: What is EN 13146-1?

EN 13146-1 is a European standard specifying the test method for determining the longitudinal rail restraint of a fastening system. It involves applying a pulling force to a section of rail secured to a sleeper and measuring the force required to cause the rail to slip. This ensures the fastener can lock the rail in place against thermal and braking forces.

The Physics of Rail Restraint

The primary function of the fastening system (clips, pads, insulators) tested under EN 13146-1 is to convert the potential thermal expansion of the rail into internal stress.

• Thermal Forces: A 1km length of rail can expand by meters if unchecked. The fasteners must provide enough friction to hold it rigid.
• Braking/Acceleration: Trains exerting traction forces try to push the rail backward. The restraint prevents the track structure from shifting.

Test Methodology

The standard outlines a precise setup to ensure repeatability:

1. Setup: A short section of rail (typically 0.5m) is mounted on a sleeper or concrete block using the complete fastening assembly.
2. Execution: A hydraulic actuator pulls or pushes the rail longitudinally at a constant, slow speed (typically around 10 mm/min).
3. Measurement: The force and displacement are recorded. The “Longitudinal Rail Restraint” is defined as the maximum force recorded before the rail slips continuously.

Comparison: EN 13146-1 vs. EN 13481 Series

It is crucial to distinguish between the test method and the performance requirements.

Relevance to CWR Safety

For Continuous Welded Rail (CWR), the results from EN 13146-1 are a primary input for track stability calculations.

• High Restraint (> 9 kN): Preferred for high-speed lines and heavy haul to ensure absolute stability.
• Low Restraint (Zero Longitudinal Restraint): Special “slide chairs” used on long bridges allow the rail to move freely to prevent structural damage to the bridge deck. These are tested to confirm they have negligible restraint.