## 3 Analysis of the Temperature Field of Steel-Concrete Superimposed Beam (SCCB)
### Transverse and Vertical Temperature Distribution Analysis  
#### 3.2.1 Vertical Temperature Gradient  
Taking the vertical temperature distribution in the center of the eastern mid-web as the research object, the 24 h temperature gradient change in the steel-hybrid beam under sunshine is analyzed, as shown in Figures 6-9. Figure 5: Distribution cloud of daily temperature field of steel–concrete composite beam. (**a**) 1:00. (**b**) 5:00. (**c**) 10:00. (**d**) 15:00. (**e**) 20:00. (**f**) 24:00. Figure 6: Vertical temperature distribution of the east side web from 1:00 to 6:00. According to Figures 6 and 7, during the period of 1:00 to 5:00, in the absence of external radiation sources, the steel beam and concrete slab continue to radiate outward and dissipate heat, and the temperature gradually decreases, reaching the daily minimum  
Figure 8: Vertical temperature distribution of the east side web from 13:00 to 18:00. Figure 7: Vertical temperature distribution of the east side web from 7:00 to 12:00. Figure 9: Vertical temperature distribution of the east side web from 19:00 to 24:00.  
temperature at 5:00 am. The temperature distribution inside the concrete slab presents an inverse \"C\" curve. Because the air in the steel beam has a thermal insulation effect, the temperature of the steel beam near the concrete slab is higher and has a certain temperature gradient. During this period, the temperature difference between the upper edge and the lower edge of the steel beam reached a maximum of 5.6 \({}^{\circ}\)C. However, the internal temperature of the steel beam is higher than the ambient temperature, and the bottom of the steel beam continues to dissipate heat, so there is a temperature gradient of 1.0 \({}^{\circ}\)C from the bottom of the steel beam. From 7:00 to 12:00, with the rise of the sun, the ambient temperature rises. Under the action of solar radiation, the temperature of the upper edge of the concrete slab increases rapidly, and the temperature of the lower edge of the concrete slab and the steel beam also increases slowly. The temperature difference between the upper and lower edges of the concrete slab gradually increases, and the temperature difference reaches a maximum of 9.0 \({}^{\circ}\)C at 12:00. The temperature inside the steel beam gradually increases, and the temperature gradient at the bottom of the steel beam decreases to 0.6 \({}^{\circ}\)C.  
As can be seen from Figures 8 and 9, the temperature gradually rises during 13:00-15:00. The temperature drops gradually from 15:00 to 18:00. The maximum temperature of the concrete slab and steel beam appeared at 15:00, which were 59.2 \({}^{\circ}\)C and 48.1 \({}^{\circ}\)C, respectively. At this time, the temperature difference between the upper and lower edges of the concrete slab reaches a maximum of 11.1 \({}^{\circ}\)C, but the temperature difference between the upper and lower edges of the steel beam is only 2.2 \({}^{\circ}\)C. With the decrease in ambient temperature and solar radiation intensity, the temperature of the upper edge of the concrete slab gradually decreases. During 14:00-18:00, the overall temperature change range of the lower edge of the concrete slab and the internal temperature of the steel beam is less than 1.0 \({}^{\circ}\)C, and the temperature gradient at the bottom of the steel beam is only 0.6 \({}^{\circ}\)C. After 19:00, as the external radiation source is lost, the ambient temperature gradually decreases, the temperature of the upper edge of the concrete slab and the steel beam begins to decrease, the temperature of the lower edge of the concrete slab slowly decreases, and the temperature inside the concrete slab gradually forms an inverse \"C\" curve. The temperature gradient at the bottom of the steel beam increased to 0.9 \({}^{\circ}\)C, and the temperature difference between the upper and lower edges of the concrete slab gradually increased, reaching 3.3 \({}^{\circ}\)C at 24:00.