Abstract: Three representative cross-section tunnels, single/double-line arch, and ellipse-like rectangle, were selected, and the FDS numerical simulation software was used to study the effect of tunnel cross-section differences on the ultra-fire resistance rating range of the tunnel wall under different wind speeds. The results show that: under the ambient wind speed, the temperature of the concrete wall of each section of the tunnel exceeds the fire resistance rating of 380 ℃. The maximum temperature of the concrete wall of the single-hole double-track tunnel and the range of the ultra-fire resistance rating are approximately 1/2 of those of the single-hole single-track tunnel and the elliptical rectangular tunnel. Mechanical ventilation can effectively reduce the temperature of the concrete wall of the tunnel, and the range of the concrete wall temperature exceeding the fire resistance rating of single-line single-hole and elliptical double-line tunnels is reduced to 1/3 and 2/5 of the ambient wind speed, respectively, and the fire development trend of elliptical rectangular tunnels is enhanced under mechanical ventilation.

Key words: tunnel cross-section, ultra fire resistance rating range, surrounding ventilation, mechanical ventilation, numerical simulation