# Numerical Study on Temperature Distribution of Steel Truss
## 6 Conclusions  
In this study, a 72-h transient temperature field analysis of a steel truss aqueduct under different conditions is conducted. Some conclusions are drawn from the results. 1. For the aqueduct full of water, the temperatures of inner surfaces contacting with water stay the same as water's temperature, which is consistent with the fact that the thermal capacity of water is a few orders of magnitude larger than that of steel. It is interesting to find that water has a limited effect on the temperature field of truss structures of the aqueduct. When water depletes, the highest temperature of inner surfaces is reached near the upper surface of the truss. Most of the inner surfaces on the truss side are in the shadow area, but the middle of the inner surfaces, which can be exposed to solar radiation in certain hours, has a relatively high average temperature. 2. For horizontal surfaces on the trusses, the biggest temperature difference (37.0 \({}^{\circ}\)C) in a summer day happens on the upper surface of the top truss, while the temperature difference in a summer day of bottom surfaces on the bottom truss is only 15.4 \({}^{\circ}\)C, which is owing to different main heat sources: direct solar radiation on the upper surfaces and ground reflected radiation on the bottom surfaces. Meanwhile, a relatively small difference exists in the heat sources of different regions of upper surfaces (or bottom surfaces) as well as the temperature on them at the same time. 3. However, compared with the temperature distribution on horizontal surfaces discussed above, the temperatures on different locations of vertical surfaces are much more complicated as the shielding of sunlight between components of the aqueduct changes with hours. In general, the eastern part is exposed to direct radiation in the morning, and the western part in the afternoon. The exposure time is determined by several factors and changes with hours. The longer the exposure time and the larger the irradiation area are, the higher temperature gets. The largest temperature difference on the vertical surface of the truss is 21.3 \({}^{\circ}\)C on the western upper truss in summer. 4. Vertical temperature gradients of surfaces B and C are obtained from the simulation. Cubic polynomials fit well with the results. The temperature fields we got in this study can be used in further study of the aqueduct's mechanic properties, and the analysis approach could assist in thermal design and health monitoring of steel aqueducts. 5. Simplified polyline temperature gradients in summer and winter are also extracted from the simulation results. This could help the engineers to have a clear and straightforward understanding of the temperature gradients on the steel truss aqueduct. It is also much more convenient to use in practical application and aqueduct design. Figure 23: Temperature gradients with different directions of the aqueduct (angles represent azimuths of vertical surfaces on the western part of the aqueduct). * 6 Parametric studies, including wind speed, latitude, and direction of the aqueduct, are carried out to evaluate the influences of these factors on the aqueduct. The results indicate that wind speed has a larger influence on the surface B, which has a relatively higher average temperature, than surface C. Latitude with a change of less than \(1^{\circ}\) can hardly influence the temperature distribution of the aqueduct. The maximum temperature change rates per degree in latitude are about 3.77% on the top truss and 2.19% on the bottom truss. Conceptualization, R.M. and H.C.; methodology, R.M., X.H. and H.C.; software, R.M. and H.C.; validation, H.C.; formal analysis, H.C.; investigation, X.H. ; resources, X.H. and R.M. ; data curation, R.M. and H.C.; writing--original draft preparation, R.M. and H.C.; writing--review and editing, X.H., R.M. and H.C.; visualization, R.M. and H.C.; supervision, X.H. and R.M. ; project administration, X.H. and R.M. ; funding acquisition, X.H., R.M.