Keywords: monitoring, weighing, speed restrictions, continuous welded rail, strain gauge, temperature.

After track works affecting the stability of continuous welded rails (CWR), speed restrictions may be applied to ensure security. Usually, theoretical tonnage accumulation is used to determine the duration of train speed restrictions. As these values of tonnage (based on an average volume of traffic) are theoretical and approximate, margins are included to determine the duration. A direct tonnage accumulation measurement may be used to improve and optimize the duration of the train speed restrictions duration.

At the present time, weighing systems exist to calculate railways undertaking royalties or to verify the distribution of the load. But these systems are permanent bulky ones with complex installations requiring rail drilling; moreover they usually only work with low speed movements. The Track Design Department of the SNCF (French National Railways) usually uses strain gauges glued on the web of the rail for high speed weighing. But this operation requires highly skilled technicians for installation and measurement.

All these considerations brought us to an evolution of our measurement principle: strain gauges are no longer directly glued on the web of the rail, but on a fish plate. The device obtained is then normally fixed on the rail. At the end, the complete measurement system (conditioning, transmitting systems, etc.) will be included inside the fish plate. In summary, this device will allow:

• Easy installation and re-use of the device,
• High speed measurements (up to 300 km/h),
• Wireless transmission,
• Robustness (during track works).

A feasibility study was conducted with success at the Track Design Department of the SNCF, including:

• A numerical approach (for modelling an indirect measurement on an hollow fish plate),
• An on-track measurement with a prototype of hollow fish plate for validation of measurement principle (precise location of strain gages, etc.), shape and materials used.

This study showed:

• The possibility of using light materials for the fish plate,
• The best shape for holes (used to include the electronic devices, the remote transmission system and the battery): fish plate continuously hollowed out,
• The necessity of a good tightening strength.

At the present time, the device is in an industrialization phase and should be operational for in track tests during spring 2012. A patent has been recorded.

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