# Study on the Mechanical Characteristics of the Sleeper Slab Track on a Long-Span Steel Truss Bridge
## 3 Test Content
### Arrangements of Displacement Sensors
#### 3.2.2 Horizontal Displacement of Resistance Test  
In the horizontal resistance test, a total of eight horizontal displacement sensors were arranged on the structure. This included four longitudinal displacement sensors and four transverse displacement sensors. These sensors were used to measure the displacement of the sleeper slab relative to the steel beam in the horizontal direction. The arrangements of the measuring points are shown in Figure 5, and the loading devices used in the horizontal resistance test are shown in Figure 6.  
Figure 4: Arrangement of vertical displacement measuring points. (**a**) Displacement measuring points of rail, (**b**) Displacement measuring points of sleeper slab, (**c**) Displacement measuring points of steel beam, (**d**) Displacement measuring points of rail and sleeper slab in lab and (**e**) Displacement measuring points of steel beam in lab. The development of the surface strain of the sleeper slab under the sine cyclic loading process is shown in Table 1 and Figure 7. The upper surface of the sleeper slab was in the compressive state during loading. The strain at the inner side of the sleeper (5 and 6) was greater than that at the middle of the slab upper surface (3 and 4), and the strain at the outside of the sleeper (1 and 2) was the smallest among the strain measuring points of the slab. During the sine cyclic loading process, the surface strain of the sleeper slab varied slightly. The average strain change rate of measuring points 5 and 6 was \(-\)4.594%. The \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sine Cyclic Loading Numbers** & **Before Cyclic Loads** & **1 Million** & **2 Million** & **3 Million** \\ \hline \multirow{4}{*}{Strain (\(\mu\varepsilon\))} & point 7 & \(-\)141.944 & \(-\)134.800 & \(-\)115.292 & \(-\)142.400 \\  & point 8 & \(-\)75.778 & \(-\)72.815 & \(-\)63.846 & \(-\)72.123 \\  & point 9 & 24.778 & 31.846 & 22.831 & 20.554 \\  & point 10 & \(-\)89.250 & \(-\)77.538 & \(-\)55.354 & \(-\)55.538 \\  & point 11 & \(-\)60.750 & \(-\)58.831 & \(-\)43.169 & \(-\)35.446 \\  & point 12 & 4.833 & 8.492 & 7.631 & 6.400 \\ \hline \hline \end{tabular} Note: positive value means pull, negative value means pressure.  
\end{table} 
Table 2: Vertical strain of the cushion. Figure 8: Vertical strain of the cushion. Figure 7: Surface strain of sleeper slab. average strain change rate of measuring points 3 and 4 was 1.263%. Only the average strain change rate of measuring points 1 and 2 reached \(-\)32.878%. This is probably because the strain values of 1 and 2 are very small. It can be seen from the above data that the sleeper slab can still maintain excellent mechanical properties after 3 million cycles of sine cyclic loading. It is well known that one of the main functions of the sleeper is to transfer the huge pressure from the rail to the track bed. The corner of the sleeper is a bulge, which can easily cause strain concentration. It has been demonstrated that the strain here is in a large state [26]. In the test, measuring points 5 and 6 were not only located at the corner of the sleeper, but also at the outside of the self-compacting concrete cushion, which means that the bottom of points 5 and 6 was in the suspended state. As a result, the location of maximum transverse compressive strain was at the inner side of the sleeper, and the average value was 97.944 \(\mu\epsilon\). Although measuring points 1 and 2 were also located at the corner of the sleeper, the strain was relatively small due to the concrete cushion support at the bottom. The development of the vertical strain of the cushion under the sine cyclic loading process is shown in Table 2 and Figure 8. The vertical strain of the cushion at the middle position of the short side was compressive strain, that at the middle position of the long side was tensile strain, and that at the corner was compressive strain. The values of tensile and compressive strain were kept at low levels. During the sine cyclic loading process, the tensile strain at the long side of the cushion remained stable.