# Solar Radiation Parameters for Assessing Temperature Distributions on Bridge Cross-Sections
## 6 Influence of Solar Radiation on Temperature Distribution on Bridge Grider Cross-Sections
### Box Grider Bridge
#### 6.1.2 Influence of Solar Radiation on Temperature Distribution on Cross-Section of Box Girder  
During the monitoring period, 2 August 2010 was a sunny day with high solar radiation. Comparisons of temperature-time curves obtained experimentally or from finite element model with or without the consideration of solar radiation are illustrated in Figure 11 (2 August 2010). The hollow points denote the measured data, the solid line denotes the calculated curves with the consideration of solar radiation, and the dashed line denotes the calculated curves without the consideration of solar radiation. The temperature contour plots obtained from finite element model with or without the consideration of solar radiation are compared in Figure 12 (15:00, 2 August 2010). In Figure 11, it can be observed that the variation trends and the times at which the highest temperatures occurred are similar for measured and calculated results on 2 August 2010. The differences between the highest measured and calculated temperatures when considering the effect of solar radiation were very small (maximum 0.2 \({}^{\circ}\)C for the two webs and 1.1 \({}^{\circ}\)C for the bottom flange). However, the highest calculated temperatures without the consideration of solar radiation were lower (maximum 1.7 \({}^{\circ}\)C for the two webs and 1.3 \({}^{\circ}\)C for the bottom flange) and had a time delay (3 h for two webs and the bottom flange). The accuracy of the solar radiation calculated by using the estimation models can meet the engineering requirements. Moreover, when solar radiation was not considered, the differences between the highest measured and calculated temperatures at the external surfaces of the box girder (1.7 \({}^{\circ}\)C for EW-1, 1.5 \({}^{\circ}\)C for WW-1 and 1.3 \({}^{\circ}\)C for B-1) were significantly larger than the differences at the internal surfaces of the box girder (0.7 \({}^{\circ}\)C for EW-2, 0.2 \({}^{\circ}\)C for WW-2 and 0.5 \({}^{\circ}\)C for B-2). This is because the influence of solar radiation on the temperature distribution decreases as the distance from external surfaces increases. From Figure 12, it can be observed that the differences between the highest calculated temperatures with or without the consideration of solar radiation were significant at 15:00 on 2 August 2010 (maximum 12.5 \({}^{\circ}\)C). The vertical temperature variation on the cross-section of box girder when considering the effect of solar radiation (19.2 \({}^{\circ}\)C) was significantly larger than that without the consideration of solar radiation (7.0 \({}^{\circ}\)C). Therefore, the influence of solar radiation should be considered in the analyses of the temperature distribution on box girders. Figure 11: _Cont._  
Figure 10: Finite element model of cross-section of box girder. Figure 11: Influence of solar radiation on temperature distribution on cross-section of box girder in summer (2 August 2010): (**a**) east web (EW-1); (**b**) east web (EW-2); (**c**) west web (WW-1); (**d**) west web (WW-2); (**e**) bottom flange (B-1); and (**f**) bottom flange (B-2). Figure 12: Temperature contour plots of box girder at 15:00 on 2 August 2010: (**a**) with solar radiation; and (**b**) without solar radiation. During the monitoring period, 16 December 2010 was a cloudy day with low solar radiation. Comparisons of temperature-time curves obtained experimentally or from finite element model with or without the consideration of solar radiation are illustrated in Figure 13 (16 December 2010). The hollow points denote the measured data, the solid line denotes the calculated curves with the consideration of solar radiation, and the dashed line denotes the calculated curves without the consideration of solar radiation. The temperature contour plots obtained from finite element model with or without the consideration of solar radiation are compared in Figure 14 (24:00, 16 December 2010).