# Temperature Distribution Characteristics of Concrete during Fire Occurrence in a Tunnel
## 6 Conclusions  
This study analyzed the effects of fire in a tunnel due to an accident involving dangerous-goods vehicles using fire simulation. Furthermore, a fire exposure test of a reinforced-concrete member was conducted using the RABT fire curve, which is employed to simulate a tunnel fire. The conclusions of this study are as follows:  
1. The results of the FDS tunnel fire analysis for each combustion material showed that diesel had a longer fire duration at the same fire intensity in comparison to the other tested fuels. As diesel is also the most commonly used fuel, it was selected as the fire source in the fire analysis that followed.
2. The results of the fire analysis showed that the peak temperature on the concrete surface was approximately 1380 \({}^{\circ}\)C and that at a depth of 60 mm, the temperature was approximately 405 \({}^{\circ}\)C. These values do not satisfy the maximum critical temperatures for concrete and reinforcement bars that have been suggested by the ITA. These maximum temperatures are 380 \({}^{\circ}\)C and 250 \({}^{\circ}\)C, respectively. When a fire corresponding to 27,000 L of diesel occurs, the desirable coating thickness of the tunnel structure is 80 mm, which is greater than 60 mm.
3. The analysis results for fire caused by dangerous-goods vehicles in the tunnel showed that at approximately 300 s after the beginning of the fire, the surface temperature of the concrete increased to approximately 1000 \({}^{\circ}\)C. This high temperature was maintained for approximately 1800 s. Therefore, on the basis of the empirical verification of the high-temperature exposure characteristics of concrete structures, the RABT fire curve was applied, in which the temperature rapidly increased to 1200 \({}^{\circ}\)C within 5 min. These results were similar to those of the analysis. Furthermore, since the maximum temperatures for concrete and reinforcement bars are specified as 380 \({}^{\circ}\)C and 250 \({}^{\circ}\)C, respectively, by the ITA, it is desirable to determine the fire damage that has been caused to the specimen on the basis of the suggested standards when an RABT fire curve with a significant temperature rise is used.
4. The results of the RABT fire experiment showed serious spalling to a depth of 60 mm, or, in other words, the point at which reinforcement bars are located in concrete. The temperature inside the concrete rose rapidly depending on the spalling. The temperature measured at a depth of approximately 60 mm, where spalling occurred, was similar to that inside the furnace. The temperature at a depth of 80 mm was approximately 420 \({}^{\circ}\)C during the rising period and 540 \({}^{\circ}\)C during the descending period.
5. On the basis of the results of the RABT fire curve experiments, 80 mm is the desirable minimum coating thickness of a tunnel concrete member in order to secure the safety of such structures during serious fires.  
Conceptualization, S.K., J.S., J.Y.R., C.P.; methodology, S.K., D.J.; writing and draft preparation, S.K., C.P.  
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) and funded by the Ministry of Education (grant no. 2017R1A2B4012678) and the Korea Expressway Corporation Research Institute as part of the research project \"Simulation and Experimental Simulation for verification of fire and explosion safety measures for vehicle fires\".  
The authors declare no conflicts of interest.