Waterproof Performance Degradation And Internal Force Redistribution Of Composite Segment Lining Under Fire

The underground space in urban core area is increasingly crowded.The shield tunneling method,which is suitable for the underground tunnel excavation,develops toward the direction of diversified cross-section forms and high space utilization.At the same time,the geological conditions and construction environment is more complex.The above development trend requires that shield tunnel segment lining has high strength,high stiffness,good quality,excellent ductility,and durability to ensure that it can solve the safety risks of large section,largely buried depth,and long long-distance shield tunnel during construction and operation period.The composite segment composed of thin steel tube(or ductile cast iron tube),concrete,shear nails,and so on can meet the requirements of urban underground tunnel construction under complicated conditions.In this paper,a combination of model test,theoretical analysis,and numerical simulation is used to study the composite segment under fire.The research on heat transfer at the interface between rectangular steel tube and concrete under the high temperature of the fire mainly adopts model test,theoretical analysis,and numerical simulation.Numerical analysis and theoretical analysis are used for the analysis of waterproof performance degradation,temperature and stress redistribution of composite segment under the high temperature of the fire.The test is used to study the heat transfer process of steel plate of different thickness and concrete under different separation and cavity heights.The temperature change curves with time are obtained.The temperature and the transition heat transfer coefficient are calculated at the interface between steel and concrete.It is found that the influence of steel plate thickness and different separation and cavity heights on the discontinuous transmission of the temperature.ABAQUS is used to establish a fine numerical model for heat transfer analysis of rectangular steel tube and concrete contact interface under high fire temperature,analysis of composite segment lining waterproof performance degradation,analysis of composite segment lining ring fire.Accurate high-temperature characteristic parameters in fire are entered in the model.The method of coupling temperature and load is used to quantitatively analyze the temperature discontinuity law of the contact interface between steel tube and concrete under high fire temperature and the influence of fire on the waterproof performance of composite segment lining.A calculation formula for the redistribution of the internal force field of the composite segment lining ring under high fire temperatures is established.The main conclusions are as follows.(1)The impact of separation and cavity:when there is no separation,the interface temperature of concrete is basically the same as the interface temperature of steel plate/ductile cast iron plate.When there is a separation,the separation is the main factor leading to discontinuity of heat transfer.The interface temperature of concrete is significantly lower than the interface temperature of steel plate/ductile cast iron plate.The presence of separation has a greater impact on temperature conduction.(2)The functional relationship between temperature difference and separation height: it can be used to calculate the interface temperature of composite segment concrete with different separation heights.(3)The influence of temperature on the gasket: when the temperature is 100℃,the stress of the composite segment waterproof gasket is slightly smaller than the stress of the gasket at room temperature,while the stress of the gasket at 160℃ is much smaller than the stress of the gasket at room temperature.The strength of the gasket is not significantly reduced within 100°C,and the strength is significantly reduced at100～160°C.(4)The temperature and stress relationship of each component: the most disadvantageous position of temperature and stress on the inner panel of composite segment,main truss beam and inner panel with joint is selected as the most disadvantageous position.The calculation formula and curve of temperature and stress are obtained by fitting function,which can be used for fire temperature and stress prediction or post disaster structural safety performance analysis.