Design and Verification of Ladder Sleepers Suitable for Rail Joints in Ballasted Tracks

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.