Continuously Welded Rail Design for Overtaking Lines Added at Existing Elevated Metro Stations

Objective To control the variations of track/bridge forces and displacements induced by adding overtaking lines at existing elevated metro stations, it is necessary to carry out comparative research on different layout schemes of CWR (continuously welded rails).

Method Taking the scenario of adding overtaking lines on both sides of an existing elevated metro station, and replacing the original four-span simply supported beams with four-span continuous beams in situ as the research object, five CWR layout schemes in three categories are arranged, i.e. installing REJ (rail expansion joint) on straight and diverging turnout tracks, installing REJ only on diverging turnout tracks, installing buffer rails on both the straight and diverging turnout tracks, installing buffer rails only on the diverging turnout tracks, and adopting CWT (continuously welded turnout). A refined calculation model for beam-track interaction on the bridge turnout is established using the finite element method. The rails and bridge main structures are simulated with beam elements, while fasteners, spacer-iron force-transmitting components, rail joints, and fixed bridge pier bearings are simulated using combinations of nonlinear and linear spring elements. Key indicators such as the temperature difference between bridge and rail, longitudinal resistance of fasteners, resistance of rail joints, resistance of REJ, and turnout geometric parameters are incorporated in the model to reproduce the force transmission pattern under temperature expansion/contraction conditions. For the five CWR schemes, the rail expansion/contraction force, turnout displacement, force on the force-transmitting component at the switch rail heel, and longitudinal force on the existing piers are calculated respectively, and the effects of each scheme on the track, bridge piers and abutments are compared.

Result & Conclusion  Installing REJ on straight and diverging turnout tracks reduces the forces and displacements of the turnout, but increases the forces on the existing piers. Installing REJ only on diverging turnout tracks is favorable to control the pier forces, but increases the turnout forces and displacements. The scheme of installing buffer rails on both the straight and diverging turnout tracks is better for turnout forces and displacements than that only installing buffer rails on the diverging turnout tracks, but the latter can improve the running smoothness on the straight turnout track. The forces and displacements of the CWT are largest, yet featuring the best smoothness and more complicated maintenance. Except for the scheme with expansion joints on both the straight and diverging turnout tracks, all other schemes need to consider the effect of switch machine displacement and strengthen the force-transmitting design at the switch rail heel.