Modified connection mode of rack system on super-slope bridge under extreme temperature load in rack railway

The construction of rack railways is widely planned across the mountainous areas of Southwest China. However, the huge differences in the daytime and nighttime temperatures in these areas easily lead to deformation mismatch between rack and bridge structures and subsequently result in unpredictable phenomena, such as connection failures in the rack system. This article then explores the vehicle-track (rack)-bridge system (VTRBS) interaction problem caused by extreme temperature loads. Guided by train-track-bridge dynamic interaction theory and considering the meshing behavior of the gear-rack and wheel-rail contact, a dynamic model for investigating the VTRBS interaction under extreme temperature load is constructed. The reliability of the rack system on a super-slope bridge under different rack and sleeper connection modes is studied using this model, and the modified connection mode is proposed. Under an extreme temperature load of -45 celcius, the reliability of the rack system is greatly affected by the rack and sleeper connection modes. When traditional fixed connections are used, the maximum stresses in the rack and fixed connection bolts are 1095 MPa and 1980 MPa, respectively, both exceeding the material strength. When using traditional fasteners, the maximum stresses in the rack and fastener bolts are 203 MPa and 38 MPa, which do not exceed the material strength. However, the elastic displacement between the rack and sleeper exceeds the allowable range of traditional fasteners. When using longitudinal resistance modified fasteners, the stresses in the rack system do not exceed the material strength, but the elastic displacement exceeds the maximum allowable range. When using elastic displacement modified fasteners, the modified elastic displacement ranges between 16 mm and 24 mm, which is within the normal working range. When using longitudinal resistance and elastic displacement modified fasteners, the modified elastic displacement ranges between 12 mm and 24 mm, which is also within the normal working range. These results provide theoretical basis for the early design and later operation and maintenance of rack railways.