The Backbone of the Bogie: EN 13103-1 and Axle Design Methodology

What is EN 13103?

EN 13103 (specifically the current version EN 13103-1) is the European Standard titled “Railway applications – Wheelsets and bogies – Part 1: Design method for axles with external journals.” It serves as the primary engineering rulebook for calculating the physical dimensions and strength requirements of railway axles.

An axle is one of the most safety-critical components on a train. If it fails, a derailment is almost guaranteed. Consequently, engineers cannot simply “guess” how thick an axle should be. EN 13103 provides a rigid mathematical framework to calculate the stresses induced by the weight of the train (static load), the dynamic forces of moving over tracks (dynamic load), and the twisting forces of braking and traction.

The “Merger” of Standards

Historically, the industry used two separate standards: EN 13103 for non-powered (wagon/coach) axles and EN 13104 for powered (locomotive/EMU) axles.

In a major move to simplify certification, these were merged into the single document EN 13103-1 (first published in 2017). Now, a single methodology covers both types of axles, provided they use external journals (bearings on the outside of the wheels). This harmonization reduces confusion and standardizes safety margins across the entire train fleet.

Key Technical Specifications

The standard outlines a step-by-step design process that every rolling stock engineer must follow:

1. Force Identification

The standard defines how to translate the mass of the vehicle into forces acting on the axle. It considers:

• Vertical Forces: The weight of the carbody plus passengers/cargo.
• Lateral Forces: The side-to-side forces experienced during curving or hunting (oscillation).
• Braking/Traction Moments: The torque applied by brake discs or traction motors, which tries to twist the axle.

2. Beam Theory Calculation

EN 13103 models the axle as a beam supported at two points (the journals) and loaded at two points (the wheels). It requires the calculation of bending moments at specific high-risk sections, such as the wheel seat (where the wheel is pressed on) and the transition radii (where the axle diameter changes).

3. Fatigue Limit and Safety Factors

Railway axles undergo billions of rotation cycles. The standard does not test for “ultimate strength” (snapping point) but for fatigue limit. It specifies the maximum permissible stresses for standard steel grades defined in EN 13261 (such as EA1N, EA1T, and EA4T).

Example: For standard EA1N steel, the permissible stress might be set around 166 N/mm² for the wheel seat, but this value is reduced by safety factors (S) depending on the reliability of the assembly and maintenance inspection intervals.

Comparison: Old vs. New Standard Structure

The following table illustrates how the current EN 13103-1 simplifies the engineering landscape compared to the previous separate norms.

Relation to TSI and Hollow Axles

Compliance with EN 13103-1 is the primary method to demonstrate conformity with the LOC&PAS TSI (Technical Specifications for Interoperability).

The standard is particularly vital for modern high-speed trains which use Hollow Axles to save weight. EN 13103-1 provides the specific bore diameter calculations to ensure that removing the center of the steel shaft does not compromise its structural integrity under high-speed dynamic loads.