## 3 Research Method
### Numerical Simulation  
The simulation results of the temperature field of a steel structure are usually used as the thermal loads for the numerical calculation of its temperature effects, so the numerical accuracy of the temperature effect depends greatly on the accuracy of the simulation results of the temperature field. Therefore, the numerical simulation of the temperature field is introduced in this paper. The temperature field of steel structures is determined by internal heat conduction and external heat exchange. The theory of heat conduction is relatively mature, and it can be calculated directly from the material properties using finite element software. Take I-shaped steel for example; Figure 1 shows the heat exchange between the steel structure and the external environment, which is divided into radiative heat transfer and convective heat transfer. Radiative heat transfer is the process of heat transfer between objects in the form of electromagnetic waves, and includes solar radiation and longwave radiation. Longwave radiation, which mainly consists of sky radiation and ground radiation, can be calculated by Equation (1) [95]. \(F_{avg}\) and \(F_{us}\) in Equation (1) can be calculated by Equations (2) and (3), respectively. \[q_{l}=\varepsilon_{f}\sigma\bigg{[}F_{avg}\Big{(}T_{g}^{4}-T^{4}\Big{)}+F_{us} \Big{(}T_{sky}^{4}-T^{4}\Big{)}\bigg{]} \tag{1}\]  
\[F_{avg}=(1-cos\alpha)/2 \tag{2}\]  
\[F_{us}=(1+cos\alpha)/2 \tag{3}\]  
where \(q_{l}\) is longwave radiation (W/m\({}^{2}\)); \(\varepsilon_{f}\) is the ratio of the radiation emitted by a surface; \(\sigma=5.67\times 10^{-8}\) W/\(\left(\text{m}^{2}\cdot\text{K}^{4}\right)\) is the Stefan-Boltzmann constant; \(F_{avg}\) is the view factor from the surface to the ground; \(F_{us}\) is the view factor from the surface to the sky; \(T_{g}\) is the ground temperature (K); \(T_{s}\) is the effective temperature of sky (K), which can be calculated by \(T_{air}-6\)K; \(T_{air}\) is the air temperature (K); \(T\) is the temperature of the surface (K); and \(\alpha\) is the tilt angle of the surface from horizontal. Figure 1: Heat transfer between the steel structure and external environment using I-shaped steel as an example. The solar radiation absorbed by the surface of the steel structure can be divided into direct radiation, diffuse radiation, and reflected radiation. Direct solar radiation refers to the radiation emitted by the sun that is directly transmitted to the surface of the steel structure in the form of parallel rays. Partial solar radiation from the atmosphere reaches the steel structure surface at different angles owing to the scatter action of gas, dust and aerosol in the atmosphere, and this radiation is known as diffuse solar radiation. Due to the reflection effect from other objects, especially from the ground, the reflected direct and diffuse solar radiation absorbed by the steel structure surface is reflected solar radiation, which can be calculated directly on the basis of the reflectivity of object surfaces and geometric mathematics. However, the direct and diffuse solar radiation are very complex and are related to many factors, such as atmospheric transparency, solar altitude angle, altitude, etc. ; the most commonly used models for their calculation include the ASHARE model, the Hottel model, and the power exponent model. The three basic components of solar radiation are shown in Figure 2.  
As the clear sky model recommended by the American Society of Heating, Refrigerating, Air Conditioning Engineers, the ASHARE model was originally developed by [PERSON] (1966), and later was modified by [PERSON] (1977).