## 3 Analysis of the Temperature Field of Steel-Concrete Superimposed Beam (SCCB)
### Transverse and Vertical Temperature Distribution Analysis
#### 3.2.2 Horizontal Temperature Distribution  
* Transverse temperature distribution of concrete slab. The transverse temperature change in the beam section does not cause vertical additional bending moment, but it leads to significant temperature self-stress. Therefore, the transverse temperature changes in the upper, middle, and lower edges of the concrete slab are studied in detail in this paper. Figures 10-12 show the transverse temperature change in the upper, middle, and lower edges of the concrete slab in one day, where the negative scale area on the horizontal coordinate represents the west side and the positive scale area represents the east side. It can be seen in Figure 10 that the overall transverse temperature of the upper edge of the concrete slab changes gently, but there is a certain temperature difference between the east and west borders. Due to the insulation effect of the steel box girder, the temperature of the concrete slab above the steel beam is always higher than the middle position, and the maximum temperature difference between the two reaches 3.2 \({}^{\circ}\)C. The upper edge of the concrete slab reaches the lowest temperature of 35.4 \({}^{\circ}\)C at 5:00, the maximum temperature of 60.2 \({}^{\circ}\)C at 15:00, and the daily temperature difference in the upper edge of the concrete slab is 24.8 \({}^{\circ}\)C.  
As seen in Figure 11, the overall trend of transverse temperature distribution in the middle of the concrete slab is the same as that on the upper slab, except for the difference in value. The temperature in the middle of the concrete slab between the steel boxes is always lower than the temperature of the concrete slab above the steel box, and the temperature difference is about 5.3 \({}^{\circ}\)C. The upper edge of the concrete slab reaches the lowest temperature of 35.5 \({}^{\circ}\)C at 5:00, the maximum temperature of 53.9 \({}^{\circ}\)C at 15:00, and the daily temperature difference in the upper edge of the concrete slab is 18.4 \({}^{\circ}\)C.  
It can be seen from Figure 12 that the temperature variation law of the lower edge of the concrete slab is similar to that of the upper and middle of the concrete slab, except in numerical value. The temperature difference between the lower edge of the concrete slab between the steel box and the lower edge of the concrete slab above the steel box reaches a maximum of 7.4 \({}^{\circ}\)C at 19:00. The minimum temperature of the whole day is 35.7 \({}^{\circ}\)C, the maximum temperature is 52.3 \({}^{\circ}\)C, and the daily temperature difference at the lower edge of the concrete slab is 16.6 \({}^{\circ}\)C.  
Figure 10: Transverse temperature change at the upper edge of the concrete. (**a**) Change between 1:00 and 12:00. (**b**) Change between 12:00 and 24:00. * Steel beam web temperature distribution. According to the positions shown in Figure 6, the temperature data of the midpoint of the east-west side web, the midpoint of the east side web and the midpoint of the COMSOL model were extracted, the temperature data inside the steel beam were analyzed, and the results were shown in Figure 13.  
Figure 11: Transverse temperature change at the middle edge of the concrete. (**a**) Change between 1:00 and 12:00. (**b**) Change between 12:00 and 24:00. Figure 12: _Cont._  
It can be seen from Figure 13 that the temperature at the midpoint of the east and west side webs and the side web on a 24 h day shows the same trend in the form of cosine function. The temperature at the midpoint of the mid-web on the east and west sides varies slightly from day to day, but the overall trend is the same. Both sides of the midpoint of the side webs are in a closed-air environment, the air flow is small, the steel box girder has a certain insulation effect, and the temperature of the east and west side webs is basically the same. The east-west side of the web presents a certain fluctuation, which is because the side of the web is in contact with the environment, and the insulation effect is weak.