Search Results (3)

Ladder sleepers were originally developed to reduce maintenance requirements in ballasted tracks by improving load distribution along the rail direction. In Japan, their design generally follows the method used for prestressed concrete sleepers, where dynamic and impact effects induced by train passage are accounted for using an impact factor. However, the impact factor and the length of the unsupported section—which compensates for ballast settlement over time—have not been sufficiently verified for ladder sleeper applications at rail joints, where the load environment is more severe. In this study, ladder sleepers designed following the criteria for general track sections were installed at rail joints in an operating ballasted track. Field measurements of bending moments under train passage were collected over 13 months, and numerical analyses were performed to evaluate the applicability of key design parameters. The impact factor at rail joints remained within a range comparable to that of general sections, confirming that a value of 2 is appropriate. In contrast, the unsupported section tended to extend over time and should be set to ~1.5 times the conventional design length. Accordingly, new ladder sleeper structures suitable for the load environment at rail joints were designed. Full article

The ladder sleeper, which is a type of longitudinal sleeper with long beams in the longitudinal direction of the rail, was developed for the maintenance-labor saving of ballast tracks. In this study, to quantify the load distribution performance of the ladder sleepers at the structural boundary, full-scale model tests were conducted to quantify the vibration transmission reduction effect of the ladder sleepers. Following that, numerical experiments were carried out using a three-dimensional numerical analysis model and it was revealed that the ladder sleeper can reduce the pressure on the sleeper bottom plane by approximately 70% when compared to conventional prestressed concrete sleepers. Furthermore, when laying the ladder sleeper at the structural boundary, it was shown that laying across the structural boundary may be more effective in reducing the pressure on the sleeper bottom plane than laying it in front of the structural boundary. Finally, ladder sleepers were installed on the commercial line and long-term measurements of the longitudinal level irregularity verified the effect of suppressing the longitudinal level irregularity of the ballasted ladder track. Full article

Despite the fact railways are seen as an environmentally friendly and sustainable form of transport, however, the train-induced vibration has been seen as a negative environmental consequence. The ballasted ladder track is one type of ballasted track with longitudinal sleepers. The elastic elements can not only protect the track structure but also control the vibration. To investigate the vibration mitigation effects of ballasted ladder track with elastic elements, a finite element - infinite element (FE-IFE) model was built considering the elastic elements of under-sleeper pads (USPs) and under-ballast mats (UBMs). This model was validated by a laboratory test. Then, the moving train load was obtained based on the multi-body dynamics (MBD)-finite elements method (FEM) analysis. The vibration mitigation effects of the ballasted ladder track with different types of elastic elements were calculated compared with the ballasted tracks without elastic elements. The results indicate that: (1) the ballasted ladder track has the advantage of vibration reduction at low frequencies, with a maximum vibration attenuation of 25.2 dB and an averaged vibration attenuation of 19.0 dB between 5 and 20 Hz through the ballast. (2) The ballasted ladder track with USPs or UBMs can provide better vibration attenuation between 30 and 100 Hz, but it induces a vibration amplification between 5 and 30 Hz. (3) The ballasted ladder track with elastic elements in different cases can provide different vibration mitigation effects. The ballasted ladder track with both USPs and UBMs can provide the best mitigation effect with an average vibration mitigation of approximately 15 dB and a maximum vibration mitigation of 30 dB between 30 and 100 Hz. Full article