# Performance-Based Analysis of Single-Layer Cylindrical Steel Reticulated Shells in Fire
## 3 Air Temperature Field Analysis During a Fire
### Fire source Location I  
When the fire source is in the center at ground level, the temperature field inside the reticulated shell is symmetrically distributed along the length and span of point A. The monitoring points A, B, and C, on the roof, are shown in Figure 6. Point A is directly above the fire source. The air temperature curves of each monitoring point are shown in Figure 7.  
Figure 5: Comparison of temperature curves between test and FDS results. Figure 6: Part of the measurement points. As shown in Figure 7, the temperature of the monitoring point indicates that the temperature of point A on the roof directly above the fire source is much higher than at the other two points. The temperature of point B is higher than that at point C, which is due to the flow characteristics of the hot smoke. The hot smoke floats up and spreads along the height of the roof so that the temperature at point B is higher than the temperature at point C at the edge of the roof. In general, the air temperature increases with the increase of the power of the fire source and with the decrease of the distance from the center of the fire source. The air temperature directly above the fire source is much higher than that around the fire source. Therefore, this shows that a curved roof will cause the convergence of hot smoke. The convergence effect increases obviously with an increase in the fire source's power. It can be seen that the temperature rise curve at the three measuring points is similar to the change form of the fire source power curve under each working condition in Figure 7. Due to the uncertainty of the flame height affected by the external environment during combustion, there are different degrees of fluctuations in each curve in the temperature stable stage. The fluctuation of the measuring point directly above the fire source is larger than that outside the fire source, and the fluctuation of the air temperature of the model with high fire source power is larger than that of the model with small fire source power, which is determined by the sensitivity of the flame action. Two types of temperature slices are generally symmetrically distributed along the center line because the fire source is located in the center at ground level and the building space is symmetric along the \(x\) and \(y\) axes. A temperature cloud chart from the two sections with the highest air temperatures during the fire was selected for analysis. When the fire source is in the center at ground level and the maximum fire source power is 20 MW, as shown in Figure 8, the temperature of the area where the fire source is located is the highest during the entire process of combustion. In the development phase of the fire (0-650 s), the fire source power increases parabolically, the height of the flame gradually increases, and flame radiation and hot smoke slowly rise to the center of the roof. In the central area, hot flue gas rises up to the roof due to air buoyancy, and it spreads to surrounding areas due to the blocking effect of the roof; therefore, the temperature on the roof rises faster than in other areas. In the stationary phase (600-2400 s), the fire source power reaches its maximum value and then remains the same. The temperature at the center of the roof reaches its peak value and fluctuates due to the instantaneous change in the flame height; however, the fluctuations are not large. The hot flue gas generated during continuous combustion continuously flows. It spreads along the edge of the roof to the surrounding wall. Finally, the temperature of the air under the roof gradually rises, and there is a clear temperature gradient between the roof and the area below. The temperature on the roof above the smoke plume is basically the peak of the entire combustion process (about 600 \({}^{\circ}\)C).