## 2 Previous Studies
### Space Structures  
Space structures are rather sensitive to temperature variations because of their high degrees of static indeterminacy [16; 17; 18]. Therefore, it is necessary for structural design and construction calculations to study the practical temperature distributions and variations in space structures. As one important prerequisite, the study of the temperature distribution laws of steel members is helpful for determining the temperature field of space structures. Many experiments have shown that the temperature of steel members along the length and thickness directions can be assumed to be uniform, while the temperature distribution of member sections along the horizontal and vertical directions is significantly non-uniform [19; 20; 21]. There are many factors that affect the non-uniform temperature distribution of steel members, such as solar radiation intensity, ambient wind speed, section size, and the surface coating of the steel member [22]. [PERSON] continuously monitored the temperature field of I-shaped steel, a rectangular tube, and a circular tube over a 90-day test period, lasting from July to September in 2015 [23]. Based on the test results, the non-uniformity of the temperature distribution was positively and negatively correlated with solar radiation intensity and ambient wind speed, respectively. Under identical conditions, the temperature distribution of small section members was mainly controlled by thermal conduction, and the maximum temperature difference of small sectionsof circular tube (\(76\times 3\) mm) was only around \(4\ ^{\circ}\)C, but the self-shadow influence of the member on temperature distribution increased gradually with the increase in section size, and the maximum temperature difference of larger sections of circular tube (\(219\times 5\) mm) could reach more than \(16\ ^{\circ}\)C. [PERSON] tested the temperature of steel plates with different surface coatings under sunlight [24]. The darker the surface coating, the higher the temperature of the steel plate, and the maximum temperature difference between steel plates with different surface coatings was up to \(19.3\ ^{\circ}\)C in summer. [PERSON] also studied the temperature effects of steel members under rigid and hinged constraints induced by solar radiation through on-site monitoring and numerical analysis [25]. The thermal deformation of all specimens, which included I-shaped steel, a rectangular tube, and a circular tube, was relatively small and less than 1/3000 of their spans. However, the thermal stress of steel members induced by solar radiation was considerable, the stress distribution was obviously non-uniform, and the maximum temperature stresses of all specimens under rigid and hinged constraints reached up to 67 MPa and 58 Mpa, respectively. This indicates that the non-uniform temperature stress of steel members induced by solar radiation needs to be studied further and considered in structural design. Based on the analysis of long-term test data, [PERSON] found one positive correlation between the average temperature and the average temperature stress of steel members, and given the corresponding linear coefficient according to the type of specimens and constraints. Considering the large number of members, the non-uniform temperature field of space structures is more complex than that of individual members. During the construction period, space structures are directly exposed to solar radiation with a significant structural temperature difference. Based on long-term monitoring data, the maximum temperature of the steel lattice structure of the Yujiabu Railway Station Building under strong solar radiation is more than \(18\ ^{\circ}\)C [26; 27]. There are great differences between the solar transmittance of different roof materials, such as glass, light steel and ETFE membrane [28]. When the roof is composed of several materials, the non-uniformity of the temperature field of space structures that are in service is more significant than that of those under construction.