## 5 Result and Analysis
### Optimization of Pavement Structure Parameters  
It is possible to reduce the tensile stresses in JPCP under dynamic loads by optimizing the pavement structure parameters to ensure its long life. As shown in Figure 10, the tensile stresses are all greater than 2.25 MPa in the cases of \"60 km/h-30 tons-C\", \"100 km/h-30 tons-C\", \"30 km/h-30 tons-D\", \"60 km/h-20 tons-D\", \"60 km/h-30 tons-D\", \"100 km/h-20 tons-D\", and \"100 km/h-30 tons-D\" dynamic loads, beyond which fatigue failure is expected under repeated vehicle loads. It can be seen from Figure 12a that the maximum tensile stress in JPCP can be reduced by varying the thickness and the elastic modulus of different layers. Considering that it is difficult to keep a vehicle traveling at 100 km/h under conditions of level D roughness in practice, \"60 km/h-20 tons-D\" and \"60 km/h-30 tons-D\" are selected in this part to optimize the pavement structure parameters. The optimization methods and their results are shown in Table 7.  
Figure 10: Tensile stress at the bottom midpoint of the longitudinal Slab2 edge (P1) under different vehicle speeds (30 km/h, 60 km/h, and 100 km/h), axle weights (10 tons, 20 tons, and 30 tons), and roughness conditions (level A, level B, level C, and level D) with the pavement structure parameters fixed as shown in Table 4.  
Figure 11: The development of the dynamic factor at the bottom midpoint of the longitudinal Slab2 edge (P1) under different vehicle speeds (30 km/h, 60 km/h, and 100 km/h), scale weights (10 tons, 20 tons, and 30 tons), and roughness conditions (level A, level B, level C, and level D) with the pavement structure parameters fixed as shown in Table 4.  
Figure 12: _Cont._  
Figure 12: The development of (a) the tensile stress under moving load, (b) the static tensile stress, and (c) the dynamic factor at the bottom midpoint of the longitudinal slab edge (P1) for the \"100 km/h-30 tonsD\({}^{\rm c}\) example with varied pavement structure parameters as shown in Table 6.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline  & \multicolumn{2}{c}{**Before Optimization:**} & \multicolumn{2}{c}{**Optimization 1:**} & \multicolumn{2}{c}{**Optimization 2:**} & \multicolumn{2}{c}{**Optimization 3:**} & \multicolumn{2}{c}{**Optimization 4:**} \\  & \multicolumn{2}{c}{**Structure Parameters Are**} & \multicolumn{2}{c}{**Increasing Thickness of**} & \multicolumn{2}{c}{**Baseline Layer from 0.2 m to**} & \multicolumn{2}{c}{**Modulus of Base Layer from 0.2 m to**} \\  & \multicolumn{2}{c}{**Shows in Table 4**} & \multicolumn{2}{c}{**Slab from 0.2 m to 0.3 m**} & \multicolumn{2}{c}{**from 0.3 m**} & \multicolumn{2}{c}{**from 1.3 GPa to 1.3 GPa**} & \multicolumn{2}{c}{**from 0.63 m**} \\ \hline Dynamic tensile stress & 20 t & 2.63 & 1.83(-30.5\%) & 2.44(-7.3\%) & 2.46(-6.6\%) & 1.92(-27.1\%) \\ (MPa) & 30 t & 3.05 & 2.10(-31.7\%) & 2.80(-8.1\%) & 2.84(-6.8\%) & 2.21(-27.4\%) \\ \hline Static & 20 t & 1.37 & 0.98(-28.5\%) & 1.27(-7.3\%) & 1.32(-3.6\%) & 1.05(-23.9\%) \\ Tensile stress & 30 t & 2.01 & 1.43(-28.9\%) & 1.85(-8.0\%) & 1.94(-3.5\%) & 1.52(-24.5\%) \\ \hline \end{tabular} Note: The values in brackets show the reduction of the stress after the optimization.  
\end{table}
Table 7: Optimization of pavement structure parameters to reduce the tensile stresses in JPCP under “60 km/h-20 tonsD\({}^{\rm c}\)” and “60 km/h-30 tonsD\({}^{\rm c}\)” dynamic loading conditions.  
It is found that increasing the thickness of the pavement slab from 0.26 m to 0.30 m or the thickness of subbase layer from 0.2 m to 0.3 m is an effective method to reduce the tensile stress by at least 27% and maintain less than 2.25 MPa under the \"60 km/h-20 tons-D\" and \"60 km/h-30 tons-D\" loading conditions and consequently improve the fatigue life of JFCP. However, it is not effective to reduce the tensile stress by increasing the thickness of the base layer or by improving the elastic modulus of base layer, as the tensile stress is reduced only by less than 8% and still maintains at high stress level of 2.25 MPa.