Study On Temperature Field Of Steel-Concrete-Steel Structure Under Refractory Structure Of Immersed Tube Tunnel

Due to the combination of high toughness and bending resistance of steel and good compressive and durability performance of concrete,the steel-concrete-steel composite structure,which has better ductility,seismic resistance,waterproof performance and safety,etc.,and significantly improved the load-bearing capacity of the immersed tube structure,is the future development direction of giant immersed tubes.The rapid heat transfer of the steel under high fire temperatures,however,has a substantial negative impact on the overall performance of the steel-concrete-steel composite construction.Thus,to preserve the safety of tunnel operation,it is essential to ensure the stability of the steel-concrete-steel combination construction under the action of fire.The thesis was supported by the National Key Research and Development Program of China," Research and Engineering Demonstration of Safety Assurance Technology for Major Water-related Infrastructure".The oversized span steel-concrete-steel immersed tube structure was used as the research object,and the temperature distribution of immersed tube structure with different refractory structures under high fire temperature was studied by combining theoretical analysis,local full-scale fire experiments,and numerical simulation.The main research findings of the thesis are as follows:(1)Fire tests were performed on the steel-concrete-steel immersed tunnel tube structure without fire protection measures to study the heat transmission law and structural damage pattern inside the structure.The test findings revealed significant damage to the structural member,necessitating the implementation of fire insulation measures on the surface of the steel-concrete-steel structure.(2)To investigate the internal temperature distribution and heat decay law of the steel-concrete-steel tube structure under various fire resistance constructions(including fireproof boards and fireproof coatings)in the high temperature of the fire,local full-size member tests were carried out.The fitting formulas between the maximum temperature and depth(depth from the upper surface of the bottom steel shell)at each measurement point inside the member were obtained.Additionally,it was discovered that temperaturetime curves of the bottom measurement points showed a clear "temperature plateau" near100°C,which characterized the relationship between the water content of the fireproof board and the highest temperature reached at the bottom surface of the steel shell.(3)The steel-concrete-steel structure’s finite element models were developed,and the internal temperature distribution law of the tube structure and the temperature change state of the steel shell’s bottom surface under various fire resistance constructions in high fire temperatures were both examined.Under various fire resistance constructions,the maximum value of the bottom surface temperature of the steel shell and the moment at which it reached its maximum value was determined.The recommendations for the choice of fire resistance measures in the actual project were then put out based on the aforementioned conclusions.(4)The maximum value of the measured temperature at the surface of the bottom steel shell of the tube structure without fire resistance measures and with fireproof board protection measures has a numerical simulation error rate between the test and simulation of only-15.70%,and the minimum is-0.07%,which is a small error.In terms of the heating trend of the temperature value at the bottom steel shell surface,there is also good agreement between the test findings and the outcomes of the numerical simulation.