# Performance-Based Analysis of Single-Layer Cylindrical Steel Reticulated Shells in Fire
## 3 Air Temperature Field Analysis During a Fire
### Fire Source Location III  
Figure 11 shows the position of the measuring points. The temperature curve of the testing points at the corner of the fire source is illustrated in Figure 12. The temperature of point D, which is directly above the fire source, is much higher than at the other measuring points. The temperatures of the other three measuring points are as follows: point B \(>\) point A \(>\) point C. Point B is located at the highest point on the roof near the gable, which is close to the fire source. Here, hot smoke can easily reach the roof and spread along the intersection of the roof and the gable. Therefore, the temperature here is the second highest, only lower than at point D, which is directly above the fire source. Point A is farther away from the fire source than is point C; however, the temperature here is higher. The reason is that the fire source is located in the corner by the wall, so hot flue gas with a high temperature (generated by combustion) can easily spread along the height of the roof and concentrate at the top of the roof.  
Figure 10: Slice temperature cloud (fire source location II).  
When the fire source is in the corner with a maximum fire source power of 20 MW, the distribution of the fire temperature field and the law of flue gas flow are very different than they are when the fire source is at the center. Because the location of the fire source is close to the roof and near the gable, the fire flame spreads along the intersection of the roof and the gable to the roof directly above the fire source, due to the increased power of the fire source, which causes the temperature to rise rapidly and form a gradient between this area and the temperature in areas further from the fire source. The hot flue gas first spreads along the upper roof and quickly flows to the other side of the gable. When it encounters the barrier, it develops in a downward direction. At the peak stage of the fire, the hot flue gas is continuously generated, which keeps the air temperature field relatively stable. At 1200-2400 s, the high-temperature region, which is over 300 \({}^{\circ}\)C, covers over half of the entire space. If the fire lasts until 3600 s, the slice temperature is reduced by 50 \({}^{\circ}\)C everywhere and is distributed evenly.  
Figure 13 illustrates the slice temperature results when the maximum fire source power is 20 MW. In the early stage of the fire, the flame continues to rise up to the roof above the fire source, and then spreads along the wall in a longitudinal direction and along the roof up to the top of the roof. The difference between this and the fire source at the midpoint of the longitudinal side is due to the blocking effect of the gable. The flame can only spread to one side along the roof on the longitudinal side and, thus, more fire plumes can laterally develop near the gable and across the apex of the roof. At this point, the temperature near the roof at \(y=2.5\) m is much higher. During the decay phase of the fire, the temperature of the flue gas decreases with an increase in density. It sinks slowly under the effect of its own weight. When the fire reaches 3600 s, the slicing temperature tends to become uniform.  
In summary, the distribution of air temperature field in large space buildings is regional and layered, which is different from the uniformity of indoor fire temperature field in steel frame buildings. The change of the position of fire source affects the distribution of air temperature field, especially the distribution of high temperature area. When the fire source is located in the middle of the longitudinal side and the corner, the temperature of the area directly above the fire source is the highest, which is above 700 \({}^{\circ}\)C. The high temperature of the local area is not conducive to the overall fire resistance of the structure; therefore, the occurrence of such fire should be avoided as much as possible.  
Figure 11: Part of the measurement points.  
Figure 12: Air temperature at each monitoring point.