Mechanical properties and safety analysis of rack railways under seismic loads with different connection methods

Rack railways are essential for mountainous railway transportation because of their ability to navigate steep slopes. However, in the tectonically active southwestern mountainous region of China, which is characterized by extensive fault zones, the behavior of rack systems on bridges under seismic loads has not been thoroughly studied. Here, this gap is addressed by developing a dynamic model of the vehicle–track–bridge system under seismic loading via train–track–bridge interaction theory. The mechanical properties of rack systems with both rigid and elastic connection methods are examined in this study, with a focus on key parameters such as rack tensile stress, shear stress, lateral torque, and bolt shear stress under varying dynamic loads. Rigid connections exhibit greater stiffness, leading to stress concentrations under coupled seismic and vehicle loads. This stiffness results in stress concentrations near bridge bearings, in which the maximum tensile stress, shear stress, and lateral torque reach 242 MPa, 226 MPa, and 2380 N m, respectively. Moreover, the maximum bolt shear stress reached 222 MPa, surpassing the shear and bending strength thresholds, further indicating a risk of localized structural failure. Conversely, elastic connections, with their buffering effects, effectively reduce stress concentrations. The maximum tensile stress, shear stress, lateral torque, and bolt shear stress were reduced to 68 MPa, 147 MPa, 1630 N m, and 120 MPa, respectively, which are all within safety limits. These findings demonstrate that elastic connections enhance the stability and safety of rack railway systems on bridges under seismic conditions. The aim of this study is to provide a theoretical basis for the design and safety assessment of rack railways on bridges in mountainous regions.