*3.1. Influence Range of High-Temperature Smoke on the Ceiling*

Figure 3 shows the influence range of high-temperature smoke on the ceiling at different bridge deck spacings. As can be seen from the figure, the range of the hightemperature area gradually decreases. With the increase in bridge deck spacing, the area where the flame plume hits the ceiling decreases. When the temperature exceeds 300 ◦C, the properties of steel begin to decrease, so the 300 ◦C isotherm is selected as the influence range of the fire temperature field. The spread distance of fire influence decreases gradually along the *x*-direction. This is because the spread distance of flame plume along the ceiling becomes smaller as the bridge deck spacing increases. However, the spread distance of fire influence first remains unchanged and then decreases along the *y*-direction. This is because the flame plume tilts along the *y*-direction due to ventilation velocity.
