# Theoretical and Numerical Simulation Research on Fire of Large-Span Spatial Structures
## 3 Temperature Field Analysis of Structure Under Different Fire Conditions
### The Temperature Distribution in the Horizontal and Vertical Directions of the Structure  
When a fire occurs inside the building, the high temperature generated by combustion gradually spreads with the smoke flow, and the path of smoke plume spreading is shown in Figure 22. The plume of this model is an axisymmetric plume. The smoke first spreads upward along Path 1 (the central axis of the plume) and reaches the top opening to flow  
Figure 21: Velocity fitting formula. Figure 20: Center velocity of the plume. out of the room. After that, the remaining smoke that does not flow out flows along the circumferential roof path 2, reaching the end wall to gradually deposit downward until the generation and discharge of the smokes reach equilibrium. Parameters such as flue gas temperature and gas concentration in the real fire environment are not uniform in time and space. The spatial inhomogeneity of flue gas temperature is reflected in both horizontal and vertical directions. Figure 23 shows the temperature change in the horizontal direction under different working conditions. The temperature change trend in the horizontal direction in the space under different air inlet areas is consistent. Due to turbulent motion, the temperature change in the horizontal direction is not continuously increasing or decreasing; there will be some fluctuations, but the overall trend of temperature change is increasing or decreasing. In the air layer, the higher the temperature, the farther away from the center of the fire source, the lower the temperature. In the smoke layer, the farther away from the center of the fire source, the temperature shows an increasing trend. The reason is that the temperature rise of the air layer is mainly due to the direct radiation heating of the flame zone, so the closer to the fire source, the higher the temperature will be. The main reason for the increase of the temperature of the smoke layer is the convective heat transfer of the smoke plume. After the smoke plume reaches the top along Path 1, it flows out at the opening, and then flows down along Path 2, that is, along the curved ceiling. After reaching the wall end, and then along Path 3, the smoke settles down from the ceiling. Since the height of the ceiling gradually decreases from the center to the periphery, at the same height level, the farther away from the center, the smoke can reach the place relatively quickly when settling, and with the passage of time, the accumulation of smoke will be higher than closer to the center, so the farther away from the fire source, the temperature will increase slightly. When the distance from the fire source boundary is less than 3 m, the temperature of the air layer rises greatly due to the direct heating effect of the flame zone. In the upper flue gas layer, due to the weakening of the combustion reaction and the cooling of the entrained air, the temperature rise is relatively small, the flow boundary is close to the flame zone, and the temperature fluctuation is large. Figure 23: Temperature variation in the horizontal direction: (**a**) CASE1; (**b**) CASE2; (**c**) CASE3; (**d**) CASE4. Figure 22: Path of smoke plume propagation. Outside the influence range of the flame zone, the difference between the maximum temperature and the minimum temperature at the same height is about 8 \({}^{\circ}\)C. Compared with the temperature of the entire flue gas layer, the difference is small. Therefore, it can be approximately considered that the temperature is evenly distributed in the horizontal direction, so as to simplify the subsequent temperature distribution model. The temperature changes along the height at different positions (x = 0 is the model boundary) as shown in Figures 24-27. It can be found that there is a clear boundary between the flue gas layer and the air layer. The temperature remains basically unchanged below the interface.