The optimal strength of shear pins: Requirements in point run-throughs

In this study, a mathematical modelling work has been carried out to investigate the potential of the use of shear pins within London Underground Switch and Crossing electric point machine drives to protect against run-through derailments. The review is based on a need to minimise the risks of derailment and to better understand the risks associated with run-through. The study has been accomplished in two stages: analytical modelling to establish the stiffness of the switch blade followed by vehicle dynamics modelling to analyse the wheel climb-out events and the resultant loadings on the shear pins. A range of shear pin strengths and vehicle-track parameters has been considered. A post-processing routine has been developed to enable a thorough study on the relationship between vehicle-track parameters, strength of shear pins, failure rates and the risk of vehicle derailment. A good agreement between the modelling results and the current shear pin’s ability to protect against derailments has been found. Ultimately, the potential to increase the strength of shear pins has been analysed in order to protect the vehicles against fatigue failure.