## 5 Result and Analysis
### Effect of Dynamic Loading Parameters  
As illustrated above, the bottom midpoint of the longitudinal Slab2 edge (P1) is selected as the critical location to be monitored, where the tensile stress will be calculated under various conditions. The dynamic axle loads generated in Figure 8 are used as the external excitation in the JPCP numerical model, and the maximum tensile stresses at P1 under different loading conditions shown in Table 5 are computed to analyze the effect of the dynamic loading parameters including the vehicle speed, the axle weight, and the pavement roughness level; the results are shown in Figure 10. The JPCP structure parameters are fixed as shown in Table 4.  
It is seen that the tensile stress at P1 (\(\sigma_{\text{x-d}}\)) increases with the deterioration of pavement roughness and the increase of axle weight and vehicle speed, reaching a maximum value of 3.13 MPa under the loading conditions of \"100 km/h-30 tons-D\". Meanwhile, \(\sigma_{\text{x-d}}\) is more sensitive to the deterioration of the roughness under a small axle weight. At a vehicle speed of 100 km/h, the maximum tensile stress under axle weights of 10 t, 20 t, and 30 t is increased by 117.6%, 183.8%, and 56.5%, respectively, when the roughness deteriorates from level A to level D. On the other hand, \(\sigma_{\text{x-d}}\) is sensitive to vehicle speed under the more severe roughness; i.e., at an axle weight of 30 tons, \(\sigma_{\text{x-d}}\) under roughness conditions of levels A, B, C, and D is increased by 1.5%, 3.1%, 6.0%, and 23.7%, respectively, when the vehicle speed increases from 30 km/h to 100 km/h.  
It is difficult to measure directly the stresses or the dynamic loads generated in pavements subject to moving vehicle loads; indirect measurement of the strain is normally conducted. Some researchers have found that the strain in pavements subject to dynamic load may increase by up to 100% for asphalt concrete pavement [31] and 75% for PCC pavement [32; 33] compared with that when loading is static, and the increase of strain is related to vehicle velocity, vehicle weight, pavement structure, etc. Therefore, it is reasonable to  
Figure 9: The stress influence lines at locations P1-P4 of Slab2 under the moving axle loading conditions of “100 km/h-30 tons-D” with the pavement structure parameters fixed as shown in Table 4.  
conclude that the stresses correspondingly increase in pavement subject to moving vehicle load, which verifies the numerical results obtained in this study.  
The dynamic factor is calculated as the ratio of the tensile stress under dynamic load to that under static load under the same axle weight conditions, and is normally used for assessing the effect of dynamic load on pavement response, as shown in Figure 11. It is seen from Figure 11 that the dynamic factor is always greater than 1 under various conditions. It increases with the roughness deterioration or the decreasing axle weight, with ranges of 0.98-1.17, 1.02-1.39, 1.11-1.77, and 1.26-2.46, respectively, for roughness levels A, B, C, and D. The dynamic factor increases more significantly with the vehicle speed under roughness level D, reaching a maximum of 2.46 which is more than double that of 1.15 used in the Chinese concrete pavement design guide [3] and 1.2 in the PCA design guide [4]. This suggests that a greater dynamic factor should be selected in the PCC pavement design guide to reflect the actual dynamic behavior under moving vehicle loads.