Study On The Temperature Field Of Subway Tunnel Fires And Structural Damage Based On Thermal-Mechanical Coupling Method

With the rapid development of China’s economy, transport services also presents flourishing, more and more subway tunnels appeared in people’s lives. Fire is a major problem requiring care when using the subway. The smoke and heat induced by fire, resulting in a sharp increase in temperature because of the deep underground tunnels, which is hazard to the personnel evacuation and structural stability. There are many domestic and foreign scholars have carried out related research in the field of fire subway tunnel currently. Considering the research status and the problems existing in the subway tunnel fire research, the following aspects were studied in this paper:Through the high temperature properties of concrete block experiment to obtain the relevant mechanical properties of concrete. Through fire ablation experiment of C30 concrete block and found that concrete experience with the rising temperature, the surface experienced by the color of gray changed to light schungite, light pink and yellow, meanwhile, the surface of the block cracks gradually widened and deepened accompanied by burst and fall off. The higher of the temperature of the concrete experience, the lower the residual compressive strength and tensile strength, and tensile strength has a larger reduction than compressive strength. The residual tensile strength after the temperature of 400 ℃ and 600 ℃ only 36% and 27% times the strength of normal temperature. When the temperature reaches 800 ℃ and above, the basic loss of bearing capacity of concrete.By associating the Heskestad ceiling temperature distribution, the Ingason maximum temperature rise beneath ceiling and the Alpert maximum flue gas temperature with no accumulation smoke and so on, combined model experiment analysis, proposed maximum temperature rise beneath the arched ceiling in subway tunnel. Through model experiments and results of previous studies, found that the temperature beneath the arched ceiling substantially longitudinally exponentially decay. Through model experiments and results of previous studies, found that the temperature beneath the ceiling substantially longitudinally exponentially decay. Furthermore, by dimensionless processing model experimental temperature, which in return obtained the longitudinal temperature distribution model in subway tunnel. Through the model experimental research, found that the highest temperature in the fire zone is in the top, followed by central, the lowest bottom. According to the characteristics of the temperature rise of the various parts, the section is divided into the radiation zone and convection zone to study, and then put forward the corresponding transverse temperature distribution model. The model experimental data testify the feasibility of Simtec LES simulation on prediction of non-uniform temperature field in subway tunnel. Then full-scale subway tunnel fire was sim-ulated studies by LES to analyze and demonstrate experimental result. Finally, a more precise temperature distribution model was proposed.An analytical method of overall stability of subway tunnel which is under non-uniform temperature field are put forward through ANSYS simulation. Exerting the non-uniform temperature field of subway tunnel fires to the ANSYS finite element analysis model to achieve coupling analysis of structural stress and non-uniform temperature field. The method overcome the defects of using standard temperature curve to heat the lining uniformly,and can reflect the changes of the force and displacement of lining caused by real fire temperature field. The results show: The deterioration and thermal expansion of lining concrete due to high temperature which increases the stress of top and central, and likely to cause structural instability. Because concrete has the thermal inertia of large specific heat capacity and small thermal conductivity, the lining surface warming fast and the trend is gradually weakened in the diameter direction. The displacements of tunnel lining are mostly in the millimeter level during fires, which has little influence on structural stability.