Bonded insulated rail joint monitoring using gap opening variation with fibre optic sensors: analytical validation and limits

The monitoring of bonded insulated joints makes it possible to overcome the limits dictated by cyclical scheduled maintenance, helping the infrastructure manager to anticipate the formation of possible failures. A field monitoring system that measures the joint gap opening variation was investigated, using optical fibres with Bragg gratings placed at the head of the two adjacent jointed rails. Through the application of the Zimmermann analytical model, a first quantitative validation of the data recorded by the monitoring systems measuring the joint gap opening variation was proposed. Based on the different types of failure of a bonded insulated joint, the debonded of insulating element of the joint was identified as a typical condition. Starting from this through a finite element analysis, some characteristic limitations of these monitoring systems were identified by assuming four different bonding scenarios.