# Geometrical Parametric Study on Steel Beams Exposed to Solar Radiation
## 2 Study Objective  
The hourly, diurnal and seasonal variation of air temperature are controlled by the amount of warming from sunrays, which is controlled mainly by the variation of solar radiation intensity. Exposed objects on the Earth's surface, including bridges, are subjected to time-dependent temperature alterations due to air temperature changes and the radiation from the Sun. Many influential factors can affect the degree of heating or cooling of the different parts of bridges. Among these factors is the sectional configuration of the superstructure. For I-steel girders and members, the depth of the web and width of flanges control the amount of targeting solar radiations on the web by controlling the length of the shaded area, while the thickness of members controls the temperature conductivity from exposed to shaded areas. Figure 1 shows that shading area of the web side facing the Sun (from the top flange) increases as the Sun moves higher in the sky during the morning hours, while the other side is completely shaded. This movement is reversed after mid-day, where the shaded area of the facing side decreases as the Sun moves down towards sunset. Figure 2 shows that for two beams with the same depth and at the same time, increasing top flange width leads to deeper shaded web areas. Shading reduces the heating of the target area as the direct heating from solar radiation is obstructed by the top flange, while the top surface is being heated at a faster rate. Thus, high temperature differences would be induced between the flanges and the web, which as discussed in the previous section, would induce unfavorable thermal stresses. Figure 2 highlights the importance of geometry of the adopted members for steel bridge superstructures, which spots the light on the need of detailed studies on the different candidate sections in such constructions. Standard sections including I-sections, channels, angles and tubes are the most used sections in bridges' steel and composite superstructures.  
Figure 1: Web shadowing from top flange.  
The literature survey conducted in the Introduction showed that several studies were carried out at the aim of better evaluation of bridge girder thermal response due to climate time-dependent variation, although, the number of experimental and numerical studies on steel girders still lags far behind those on concrete sections. Moreover, despite the importance of geometrical parameters like member depth, width and thickness on temperature sectional variation, very few studies have focused on these parameters. Aiming to fill the knowledge gap in this area, an I-steel beam equipped with temperature sensors was installed in the field and a finite element study was conducted. The main focus of this research is to better understand the combined influence of geometrical parameters as functions of the effective main parameters like depth, width and thickness of sections.  
In the steel construction industry, the work may be interrupted for many reasons and for long times, which leaves the structural sections exposed to the changing environmental thermal loads. In the case of extreme thermal conditions, like high summer solar radiation intensity or high daily temperature fluctuation, effective thermal stresses, deformations or movements may be induced in the sections, which require a structural evaluation. This research focuses on the most important geometrical parameters controlling the thermal response of steel members under such conditions. Therefore, the outputs of this research are useful to understand the time-dependent variation of temperatures and stresses in steel sections during the construction period where the whole structure is exposed to open environments.