## 5 Conclusions  
In this study, experimental and analytical research was conducted to investigate the fire resistance performance of HCSs. Two HCS specimens were fabricated, where the cross-sectional depth was set as a variable. The temperature distribution in the section and the deflection of the member according to the fire exposure time were measured and analyzed comprehensively. An FE analysis was conducted on the HCS under fire, and the rationality of the FE model was verified via comparison with the test results. In addition, the HCS depth, span length, hollow ratio in a section, cover thickness of concrete, and load ratio were set as key variables to perform the parametric analysis. The fire resistance performance of the HCS was then evaluated according to each variable. The conclusions obtained from this study are as follows:  
1. In 2 h of fire exposure, the temperature increase in the upper part (i.e., unexposed surface) of the D200-T7 and D265-T8 specimens was 42.5 K and 33.3 K, respectively, which are extremely low and correspond to 19-24% of the temperature increase limit (180 K) specified in ISO 834-1. In addition, it was confirmed that the HCS demonstrated excellent insulation and integrity performance because no flame penetration was observed in either specimen.
2. The maximum deflection that occurred in the D200-T7 and D265-T8 specimens was 97.2 and 76.7 mm, respectively, which were only approximately 27% of the deflection limit presented in ISO 834-1. Therefore, it can be concluded that the load-bearing performance of the D200-T7 and D265-T8 specimens was excellent during a fire.
3. The fire resistance performance of the HCS was evaluated via a nonlinear FE analysis, and the FE model demonstrated excellent accuracy in evaluating fire resistance behavior characteristics, such as the temperature distribution in the cross-section and the deflection of specimens with respect to the fire exposure time.
4. The results of the parametric analysis based on the verified FE model showed that the deflection tended to decrease as the depth of the HCS increased. This is because the heat transfer rate within the cross-section decreased as the heat capacity of the HCS section increased at the same time when the flexural stiffness of the section increased significantly with the depth. In addition, the deflection of the HCS increased significantly with the span length. However, when the vertical deflection of the HCS was normalized to the limit deflection presented in ISO 834-1, the normalized deflections showed similar values regardless of the HCS depth and span length. This is because the limit deflection calculation formula presented in ISO 834-1 reflects the effects of the section depth and span length reasonably.
5. Compared with other variables associated with the HCS member details, the load ratio exerted a more significant effect on the deflection of the HCS subjected to fire. As the load ratio increased, the vertical deflection normalized to the limit deflection increased proportionally. Therefore, to obtain more accurate evaluation results pertaining to the fire resistance performance of HCSs, the magnitude of the live load exerted during a fire, as well as details regarding the member should be determined appropriately.  
Original draft manuscript, I.H.; Validation, K.D., S.-J.H.; Investigation, S.-H.C., H.J.; Supervision and Review Writing, K.S.K. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Korea Agency for Infrastructure Technology Advancement (KAIA) grant funded by the Ministry of Land, Infrastructure and Transport (Grant 2 ICTAP-C163892-01). Also, the sixth author, [PERSON], would like to acknowledge that this research was supported by the Basic Study and Interdisciplinary R&D Foundation Fund of the University of Seoul (2021).  
Not applicable.  
Data Availability Statement: The data presented in this study are available on request to the corresponding author.  
The authors declare no conflict of interest.