# Investigation of Load Environment and Bending Load Capacities of Aged Prestressed Concrete Sleepers
## 2 Investigation of Load Environment of PC Sleepers
### Investigation Results
#### 2.2.1 Measured Wheel Loads and Bending Moments of PC Sleepers
PC sleepers are commonly provided rail seat (central void) support during track maintenance. Our findings suggest the possibility of increasing the negative bending moments at the center sections of PC sleepers by providing center support. Figure 8: Comparison of analysis and measurement results. Figure 7: Measurement results: (**a**) wheel loads; (**b**) bending moments (five continuous sleepers). Figure 10: Numerical analysis results of effects of various parameters on bending moment at center section. (**a**) Support condition R (Table 2); (**b**) support condition C (Table 2). Figure 9: Numerical analysis results of effects of various parameters on bending moments at rail seat sections: (**a**) trail speed; (**b**) vehicle occupancy rate; (**c**) spring constant of track pad; (**d**) spring constant of ballast; (**e**) amplitude of rail surface roughness; (**f**) support condition R (Table 2); (**g**) support condition C (Table 2). Figure 11 shows the numerical analysis results of all cases shown in Table 2. As shown in the figure, the positive bending moment at the rail seat section did not exceed the DDM. In the cases in which the sleeper was uniformly supported or the spring constant under the rail was reduced to 1/2, 1/5, or 1/10 of that at the center section, the negative bending moment at the center section did not exceed the DDM. In contrast, when the spring constant under the rail was 1/100 of that at the center section, this bending moment exceeded the DDM. Figure 12 shows the numerical analysis results of the case in which the rail surface roughness was measured at the rail joint of the conventional line (Figure 6). Shinkansen trains do not encounter this scenario, but if the amplitude of the rail surface roughness ever becomes approximately 2.5 mm, such as at the rail joints, the bending moment may exceed the DDM. Furthermore, if the amplitude becomes approximately 7.5 mm, the bending moment may also exceed the yield moment of steel. The above results indicate that the primary factor causing cracks and bending fractures in the target PC sleepers was the rail surface roughness, which had large local amplitudes, such as at the rail joints. In addition, assuming the PC sleepers had center support, the negative bending moments at the centers of the sleepers may increase. Therefore, the current track maintenance practice in Japan, that is, providing PC sleepers with rail seat (central void) support, should be continued. Although wheel flats were not considered in this study, their effects should be verified in the future because they generate impact loads  
Figure 11: Numerical analysis results of all cases. (**a**) Rail seat section; (**b**) center section. Figure 6:0 Numerical analysis results of the case in which rail surface roughness is measured at rail joint of conventional line (Figure 6). in the same way as rail surface roughness [3; 26; 27; 28]. However, if the current maintenance level of wheel surfaces in Japan is maintained, impact load due to wheel flats will be unlikely, so the numerical analysis in this study is worth evaluating.