Stress and Fatigue Analysis of a Fiberglass 3rd Rail Support Bracket

For mass transit rail systems employing a 3rd rail to provide the electric traction power, the 3rd rail support bracket must have the capability to withstand the dynamically applied service loads while also providing the necessary electric arc resistance. To meet the arc resistance requirement, fiberglass brackets have been steadily replacing metallic type brackets in fire retardation critical locations; therefore it was necessary to validate their structural performance when used in general service. To this end, a general stress analysis was performed on a representative support bracket to investigate potential stress profiles experienced under various static loading conditions. Historically, metallic brackets have not been susceptible to fatigue failures in service. In order to determine fatigue life characteristics of fiberglass brackets, service strains were collected and analyzed to compare the behavior of the fiberglass and metallic brackets and evaluate whether the service life of the new material is sufficient. Furthermore, the fatigue life of a support bracket is highly dependent on the operational conditions. Thus, a service fatigue life analysis was performed to determine the bracket’s response to the variation of operating environment parameters such as the 3rd rail material and track location. From the analyses performed, it was concluded that the current design was not sufficient in replacing the metallic brackets. A possible redesign was then analyzed and it can be shown that a fiberglass material is suitable for the service application if the proper bracket design is incorporated.