Dynamic characteristics of rack vehicle under bridge pier settlement

To study the basic dynamic characteristics of a rack vehicle system under pier settlement, a coupled dynamic model of the rack railway vehicle–rack (track)–bridge system in a mountain rack railway system is established based on the vehicle–track–bridge dynamic interaction theory and gear dynamics. This model accounts for the nonlinear meshing behavior of the gear–rack and the nonlinear contact behavior of the wheel–rail. The meshing behavior of the gear–rack and the dynamic characteristics of the rack vehicle under single pier settlement, double piers uniform settlement, and double piers non-uniform settlement are analyzed using this dynamic model. Meanwhile, the dynamic meshing characteristics of the gear–rack and the basic vibration characteristics of the rack vehicle under different pier settlement types and slopes are compared. Results indicate that, compared with slope, the magnitude of pier settlement has a more pronounced effect on rack vehicle vibration. Under different pier settlement types, the main frequencies of vertical and longitudinal vibration of the rack vehicle are 1–2 Hz and 8–9 Hz, respectively. Single pier settlement, double piers uniform settlement, and double piers non-uniform settlement exhibit the same effect on the running performance of the rack vehicle. Pier settlement increases gear offset, leading to instability in gear–rack meshing, resulting in engagement failure and intensified vehicle vibration. Therefore, vibration control can be realized by improving the gear–rack engagement stability.