# Refined 3D Solar Temperature Field and Effect Simulation of Ultra-High Steel Bridge Pylon
## 5 Temperature Effect of Bridge Pylon  
### Thermal Stress  
The thermal stress variations of the bridge pylon are shown in Figures 16-18. The thermal stresses of each pylon walls are mainly related to the total amount of solar radiation received. The thermal stress distribution of different pylon walls on cross-section A-A is show in Figure 16a. In spring and autumn, the maximum thermal stress are south walls, and the stress can reach 20 MPa at 13:00. There is a certain stress difference between the east and west pylon columns under the influence of mutual shielding effect, and the maximum thermal stress difference can reach 8 MPa for east walls at 10:00 and for west walls at 16:00. Figure 16b shows the vertical stress distribution of the bridge pylon at 16:00 in spring and autumn. The mutual shielding effect between the pylon columns has little effect on the thermal stress. The stress drops sharply at the beam because the back of the cross beam is completely in the self-shadowing areas. Significant mutation of thermal stress exists in the shaded area of the cross beam, and the maximum thermal stress for the west wall of east pylon column can be reduced by 18 MPa compared with the adjacent sunshiny area.  
In summer, the mutual shielding effect between the east and west pylon columns is most obvious. The thermal stress distribution of different pylon walls on cross-section A-A is show in Figure 17a. There is an obvious thermal stress difference between different pylon columns at 9:00 and 16:00 under the influence of mutual shielding effect between the pylon columns; the maximum thermal stress can reach 21 MPa for the west wall of the west pylon column at 16:00; at the same time, the maximum thermal stress difference between the outer surfaces of the east and west pylon columns can reach 15 MPa for the west walls. Figure 15b shows the vertical stress distribution of the bridge pylon at 16:00. The maximum thermal stress in the shaded area can be reduced by 13 MPa compared with the adjacent sunshiny area because the west wall of east pylon column is sheltered by the west pylon column.  
In winter, there is no mutual shelter between the pylon columns. Figure 18a shows the thermal stress distribution of different pylon walls on cross-section A-A. The thermal stress on the south walls is the largest in the whole day, and the maximum tensile stress can reach 27 MPa at 12:00, and the thermal stress difference between the south and north walls reach a maximum of 17 MPa for the whole year. The thermal stress difference between different pylon columns is small, and there is no thermal stress difference on the south walls. The maximum thermal stress differences between the outer surfaces of the two pylon columns can reach 3 MPa for the east walls at 10:00 and the west walls at 16:00, respectively. Figure 18b shows the vertical stress variation diagram of the bridge pylon at 12:00. Because there is no shading relationship between the two pylons, the thermal stress variation trend of different pylon walls is consistent, and the thermal stress at the beam on the west wall of east pylon column is slightly abrupt due to the shadow occlusion of the cross beam.  
Figure 16: _Cont._Figure 16: Stress curve of pylon in spring (autumn): (**a**) Thermal stress curve of cross-section A-A. (**b**) Vertical stress distribution of bridge pylon at 16:00.  
Figure 17: Stress curve of pylon in summer: (**a**) Thermal stress curve of cross-section A-A; (**b**) Vertical stress distribution of bridge pylon at 16:00.