Experimental Study On High Temperature Thermal Bridge Effect Of Steel-concrete-steel Immersed Tube Tunnel Structure In Fire

The large size,marine and river environments,deep-water conditions,and other factors of the submarine large-diameter immersed tube tunnel make it much more susceptible to severe consequences in the event of a fire than traffic tunnels on land.Maintenance is also extremely difficult.When a fire occurs in the tunnel,the enclosed environment generates extremely high temperatures that far exceed the limit temperatures of steel and concrete materials,causing a thermal bridge effect due to the different thermal parameters of steel and concrete.This effect leads to wall condensation and mold inside the tunnel,reducing the fire resistance of the lining structure and affecting long-term postdisaster safety operations.Therefore,studying the thermal bridge effect of the steelconcrete composite structure is of great practical significance.Based on the national key research and development program,“The Shenzhen-Zhongshan Cross-River Tunnel Project-Key Technology Research on Super-Large Span Steel-Shell Concrete Immersed Tube Tunnel Joint Structure and Fire Prevention,” this thesis focuses on the following work:(1)Survey of fire-resistant design and theoretical calculation of thermal bridging effects in steel shell concrete composite immersed tunnel: Extensive research was conducted on tunnel fires both domestically and internationally to identify the causes and characteristics of such fires.A survey was conducted on the impact of thermal bridging effects on building structures and fire resistance studies in steel shell concrete composite structures to understand the harm caused by thermal bridging effects on tunnel lining structures.Through theoretical analysis of thermal bridging,the heat transfer range of thermal bridging effects and methods of heat loss calculation were determined.(2)Experimental study of high-temperature thermal bridging effects on steel shell concrete immersed tunnel structures during fire: Based on the relevant fire-resistant design principles of immersed tunnel structures,an experimental study on thermal bridging effects was conducted on a local 1:1 component of the steel shell concrete immersed tunnel roof.The study provided feedback on the temperature distribution of the cross-section of the steel shell immersed tunnel section of the Shenzhen-Zhongshan Cross-River Channel under the RABT curve during a fire.The existence of thermal bridging effects and the law of their impact on the bottom of the steel shell during hightemperature fire in the presence of a 30 mm fireproof board were verified.The fireresistant design of the steel shell immersed tunnel section of the Shenzhen-Zhongshan Cross-River Channel under high-temperature fire was also validated.(3)Numerical analysis of the impact of high-temperature thermal bridging on steel shell concrete structures and countermeasures for thermal bridging blockage: A numerical model of a steel shell concrete composite component and immersed tunnel section with a similarity ratio of 1:1 was established using ANSYS.The temperature distribution of the steel shell concrete composite component under high-temperature fire was simulated,and the range of the impact of thermal bridging effects on the bottom plate of the steel shell with a 30 mm fireproof board and the heat loss were calculated.The fire resistance limit of the steel shell concrete immersed tunnel section was simulated with a 30 mm fireproof board,and the validity of the experimental conclusions on high-temperature thermal bridging was verified and compared.Several commonly used methods for tunnel fire resistance were introduced,and the thermal distribution at the bottom of the steel shell structure under 25 mm,30mm,and 35 mm fireproof boards was tested in the field.Finally,countermeasures and measures for thermal bridging blockage under high-temperature conditions were determined.