Reliability of super-slope rack railway under bridge pier settlement

Bridge pier settlement always occurs on the super-slope rack railway, which has serious impact on reliability and stability of rack-bridge system. Aiming at this issue, a coupled dynamic model of the super-slope vehicle-rack (track)-bridge system under pier settlement is established considering gear-rack nonlinear meshing behavior, wheel-rail nonlinear contact behavior and pier settlement. On this basis, the mechanical characteristics of gearrack system induced by pier settlement are studied. Then, the dynamic influences of two common gear-rack connections (rigid connection and elastic connection) on the adaptability and safety of this system are discussed. Finally, the safety control value of pier settlement of the large-slope railway in mountainous areas is proposed. Results show that pier settlement potentially leads to fracture of gear-rack fasteners under multi-loads such as gear-rack meshing and wheel-rail contact. When the rack and the sleeper are rigidly connected, the maximum shear stress of the fastener is 346.43 MPa when the settlement is 10 mm, which seriously exceeds the standard limit (235 MPa). When they are elastic connected, the maximum shear stress of the fastener is 262.80 MPa, slightly exceeding the limit value. The structural stress of rack is far less than the tensile strength of rack. Under the two connection modes, the maximum deformation of the rack is 14.02 mm and 11.08 mm respectively, which is about 140% and 125% of the pier settlement. The main frequencies of the vibration of the rack are located at 70 - 80 Hz and 65 - 70 Hz respectively. Pier settlement has a significant effect on the stress of the fastener and the deformation of the rack, but has little effect on the vibration and stress of the rack railway.