# Numerical Study on Temperature Distribution of Steel Truss
## 5 Results and Discussion  
Several key points (A1, A2, B1, B2, C1, C2, D1, D2) on different surfaces are selected to show the temperature changes over 72 h in summer (16 to 19 July), as illustrated in Figure 11. A1 and A2 are points on the western and eastern top surface A of the aquduct separately; B1 and B2 are points on the western and eastern vertical surface B of top trusses  
Figure 10: Numerical simulation process for the truss aquduct under solar radiation. separately; C1 and C2 are points on the western and eastern vertical surface C of bottom trusses separately; D1 and D2 are points on the western and eastern bottom surface D of bottom trusses separately. Although the points A1 and A2 are not on the same surface, the surfaces where they are located are symmetric and could be formulated into one group \"surface A\". This rule goes for B1/B2, C1/C2, D1/D2. For the surfaces on both top and bottom trusses, almost no differences exist in the two working conditions, which means that the cooling effect of water on the truss structure is limited. However, we can see from Figure 12 that the temperatures of inner surfaces of the empty aqueduct change by a large margin, while those of aqueduct full of water remain unchanged (33 \({}^{\circ}\)C), which demonstrates water's ability of cooling during the day and keeping warm during the night on the contact surface. The temperature variations of western and eastern parts are distinct on the vertical surfaces B and C and similar on the horizontal surfaces A and D. In details, the temperature variations on the top surface A in both parts are almost the same with just a little difference (about 2.15%) in the peak temperatures (65.80 \({}^{\circ}\)C in the eastern part and 64.38 \({}^{\circ}\)C in the western part). The reason for the phenomenon is that the top surface A enjoys the same solar radiation, but the heat conducted from the side vertical surfaces, which though only occupies a small proportion, is different. The temperature variations on the vertical surface B of top trusses on both sides are significantly different as the solar radiation and shadow condition at each hour on each side are different. B1 on the western part has more solar radiation than B2 on the eastern part, and thus its peak value (51.35 \({}^{\circ}\)C) is a little higher than that of the eastern part (50.24 \({}^{\circ}\)C),  
Figure 11: Temperature changes over 72 h on the aqueduct in summer. even though the average hourly air temperature in the morning is usually higher than that in the afternoon. The direct radiation on each surface is different by the hour, and thus a phase difference has been found in temperature variations on the eastern and western sides. The same reason can also be applied for the temperature variations on the vertical surface C of bottom trusses. The peak temperatures of C2 and C1 in the eastern and western parts are 48.25 \({}^{\circ}\)C and 44.83 \({}^{\circ}\)C, respectively. It should be noted that heat conduction between different components plays an important role here. The average temperatures of surfaces B and C are significantly influenced by the adjacent surfaces (A and D separately). As surface D has a much lower temperature than the top surface A, a lower temperature is presented at C1 and C2 on the bottom trusses than that at B1 and B2 on the top trusses at the same time. More discussions about temperature distributions on vertical surfaces B and C are shown below. The bottom surface D of bottom trusses does not have direct radiation, and the differences of temperature variations between D1 and D2 on both parts are no more than 0.7%. The maximum temperature is about 47.1 \({}^{\circ}\)C.  
Besides, the time at which surfaces reach the highest temperature is also distinct between surfaces. The temperatures of the top surface A on top trusses reach a climax at about 2 p.m., while those of the bottom surface D on bottom trusses at 12 p.m. to 2 p.m. The time for vertical surfaces B and C to reach the highest temperature depends on their locations.