# Investigation of Load Environment and Bending Load Capacities of Aged Prestressed Concrete Sleepers
## 4 Conclusions  
In this study, the actual load environment of PC sleepers was investigated via field measurements on commercial lines. In addition, numerical analyses were conducted to verify the effects of various parameters on the bending moments of PC sleepers. Moreover, aged PC sleepers installed on commercial lines were collected and subjected to bending tests specified in JIS E 1201 to evaluate their bending load capacities. The findings of this study are summarized below.  
Figure 14: Relationship between bending load-bearing capacities of PC sleepers and passing tonnage. (**a**) Positive bending moments at rail seat section; (**b**) negative bending moments at center sections.  
Figure 15: Relationship between bending load-bearing capacities and ages of PC sleepers. (**a**) positive bending moments at rail seat sections; (**b**) negative bending moments at center sections.  
According to the field measurement results of the wheel loads and bending moments of the PC sleepers, the maximum wheel load was 79.51 kN and the maximum bending moment at the rail seat section was 3.81 kN\(\cdot\)m. The measured values were smaller than the design values. The wheel load was 49.7% of the design wheel load of 160 kN, whereas the bending moment was 34.7% of the DDM of 10.95 kN\(\cdot\)m. In addition, neither the wheel load nor the bending moment depended on train speed.
2. The numerical analysis results indicated that the positive bending moment at the rail seat section was unlikely to exceed the DDM. However, the negative bending moment at the center section may exceed the DDM if center support were provided with a reduced spring constant under the rail (the \"hanging\" rail seat section). In addition, the bending moment increased with the rail surface roughness, so the rail should be kept smooth.
3. The results of the JIS E 1201 bending tests on the aged PC sleepers showed that the crack generation load and ultimate load decreased gradually with increases in age and passing tonnage. However, all samples satisfied the JIS standard \(P_{\rm cr}\) and \(P_{\rm u}\) values. Furthermore, the bending moments generated in the PC sleepers during train passage were considerably smaller than the crack generation loads and ultimate loads during the bending tests.
4. Thus, Japanese PC sleepers aged over 50 years currently satisfy the standard flexural fracture values specified by the JIS, and safety is not immediately compromised.  
In the future, we plan to formulate a maintenance management plan and a replacement plan for PC sleepers according to the service life of a PC sleeper obtained in this study. We also recommend the continuation of maintenance and management practices that do not generate impact loads. Present track maintenance work, which involves the use of rail seat (central void) support for PC sleepers and is commonly practiced today, should also be continued to maintain the safety and stability of railway transportation.  
Conceptualization, T.W.; methodology, T.W., K.G. and S.M.; software, T.W. and K.G.; validation, T.W., K.G. and S.M.; formal analysis, T.W.; investigation, T.W., K.G. and S.M.; resources, T.W.; data curation, T.W.; writing--original draft preparation, T.W.; writing--review and editing, T.W.; visualization, T.W.; supervision, T.W.; project administration, T.W. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors would like to thank the West Japan Railway Company for the significant cooperation in some field measurements of this study.  
The authors declare no conflict of interest.