Experimental Research on the Structural Performance of Shield Tunnel Segments Subjected to Different Fire Temperatures

In order to determine the damaging effect of different fire temperatures on a segment, experimental research was carried out on the structural performance of segments subjected to different fire temperatures. A temperature plateau occurred when the temperature reached 100°C. There were two temperature layers across the 300 mm thickness of the segment due to heating on one side only, and the temperature gradient within 0–50 mm was much more significant than that within 50–300 mm. The concrete spalling and the cracking initiated on the fired surface of the segment were severe; the maximum depth of concrete spalling on the fired surface of the segment at different fire temperatures was 600°C: 15 mm; 800°C: 45 mm; and 1,000°C: 67 mm; further, the main reinforcement was exposed or even softened. Cracking was also initiated on the unfired surface, and even penetrating cracks developed on the side surface. The damage at both ends of the segment was more severe than that in the center. The fire temperatures were 600°C, 800°C, and 1,000°C, the maximum midspan deflections were 5.27, 7.83, and 11.79 mm, the maximum midspan axial forces were 65.58, 208.41, and 333.63 kN, and the maximum reinforcement stresses were 22.49, 35.08, and 52.63 MPa, respectively. The mechanical parameters of the segment increased during the firing process and recovered during the cooling process, which is equivalent to a loading and unloading cycle for the segment. This study advances the understanding of the structural performance of shield tunnel segments subjected to different fire temperatures.