## 1 Introduction  
The concrete tower is an important component of cable-stayed bridges, suspension bridges, and other structural systems. Cracks in thin-walled structures (e.g., the main concrete tower) during the service period have become a new problem for mass concrete structures [1, 2]. In particular, the solar radiation temperature variation will cause the temperature difference between the inner and outer walls of the tower column, forming a certain temperature difference stress, which often exceeds the stress generated by the structure's dead load, live load, and other loads, and usually leads to excessive local stress and crack failure [3, 4, 5]. At present, the research on the temperature effect of concrete bridge structures mainly focuses on the upper concrete box girder structure, while the temperature field effect of the lower structure is rarely studied, such as the prestressed concrete continuous rigid frame bridge, cable-stayed bridge, concrete piers and tower columns of suspension bridges [6]. [PERSON] et al. [7] proposed a numerical simulation analysis method for the temperature field and stress field of concrete through real-time monitoring of the instantaneous temperature field and strength field of the internal temperature of concrete. [PERSON] et al. [8] proposed the solar temperature field model of the main tower of the cross-sea cable-stayed bridge through transient heat transfer analysis. By introducing major parameters such as solar elevation angle, azimuth angle, and radiation absorption coefficient, the accuracy of the proposed model was verified by comparing the measured data of the temperature field with predicted values. [PERSON] et al. [9] investigated the influence of solar temperature difference on the deviation and stress of the cable tower under the condition of onsite monitoring of the construction process of the Tieluoping super-large bridge. [PERSON] et al. [10] investigated the thermal stress of the bridge tower, indicating that the generation of vertical cracks in the bridge tower was closely related to the temperature field inside the concrete tower. In addition, concrete cracks would close and re-open under the action of different temperature fields. [PERSON] et al. [11] reduced the size of a concrete arch bridge by five times, and the calculated temperature isoline and temperature time-history curve were in good agreement with the measured values, which verified the accuracy of the finite element model. Subsequently, the verified finite element model was used for parameter analysis. The influence of thermal parameters on thermal behavior was discussed, and an effective thermal control method was proposed. [PERSON] et al. [12] took a cable-stayed bridge with a steel box girder as an example to discuss the influence of temperature on the beam deflection at different time scales. Results show that the temperature difference of the beam, as well as the temperature gradient, will lead to a large deflection. In general, it could be concluded from the abovementioned investigations that the characteristics of the thermal stress of the main tower induced by the temperature variation differ from each other, mainly depending on the appearance and geometry. However, few studies are focused on the effect of the temperature field on the thermal stress of the unique gate-shaped steel-concrete composite main tower of the Nanjing Xinshengwei Yangtze River Bridge (i.e., the engineering background of the present study), which is with a main span of 1760 m. Therefore, it is necessary to comprehensively investigate the characteristics of the thermal stress of the main tower of the Nanjing Xinshengwei Yangtze River Bridge.