## 1 Introduction
In view of this, domestic and foreign scholars have carried out relatively extensive research on a three-dimensional temperature field calculation of the bridge tower structure, using two main research methods: an actual data analysis method based on the actual project or test model and a simulation analysis method based on the finite element theory. [PERSON] et al. [9; 10] analyzed the change of the temperature difference along the height and thickness of the tower wall with time in different seasons and obtained the most unfavorable distribution of the positive and negative temperature difference based on the monitoring temperature data of the concrete tower of a suspension bridge, but did not give the change rule of the temperature field in different directions. [PERSON] et al. [11] analyzed the temperature field of the bridge tower of the Anqing Yangtze River Bridge based on the monitoring data. The results show that the temperature of the shaded part is much lower than that of other parts, and the temperature of the external surface and the ambient temperature have the same trend. Additionally, the difference between the temperature of the structure and the air can be well-fitted. [PERSON] et al. [12] studied the temperature field of a concrete bridge tower through the monitoring data. The results show that the maximum temperature difference and the most unfavorable temperature effect on the bridge tower appear in winter. [PERSON] et al. [13] collected the temperature monitoring data of a bridge in one year based on the health monitoring system of a bridge, analyzed the distribution law of the sunshine temperature field of the bridge, and put forward a calculation mode of the vertical temperature gradient and temperature difference of the bridge tower. The above method of bridge structure temperature field analysis based on the monitoring data of an actual engineering or test model can collect the real temperature data at the measuring point, but due to the limitations of the measuring point and the monitoring conditions, the data results are often unable to fully reflect the specific situation of the structure's temperature field, and the error is large. Additionally, the temperature field data monitoring process generally lasts for a long time, and the efficiency is low. However, the numerical simulation method has been favored by many researchers and engineers and has become one of the mainstream methods for the calculation and research of the temperature field of bridge structures at this stage because it is not limited by the above conditions and can realize the rapid calculation of the temperature field. The research on the boundary conditions of the temperature field of the bridge structure is relatively mature in the simulation analysis of the temperature field of the bridge structure. Therefore, the most critical problem is to consider the influence of real-time sunshine and shadow on the calculation results of the temperature field of the structure in the process of accurately simulating the three-dimensional temperature field of the bridge structure. However, the sunshine shadow occlusion of the structure is in the process of dynamic change with the change of the solar orientation in a day. How to accurately and quickly recognize the dynamic shadow occlusion area of the structure and apply reasonable solar radiation boundary conditions to the shadow occlusion area has become the premise for realizing the accurate simulation of the three-dimensional temperature field. In response to this problem, many scholars have carried out corresponding research. Early scholars carried out shadow shading research on relatively simple box girder structures. [PERSON] and [PERSON] et al.