考虑接触热阻的钢壳沉管隧道结构火灾温度场研究

Fire Temperature Field of Steel Shell Immersed Tunnel Structure Considering Contact Thermal Resistance

钢壳沉管隧道在火灾高温下易出现强度退化、结构承载性能下降甚至失稳破坏等情况,因此有必要开展火灾高温下钢壳沉管隧道结构温度场分布规律等基础研究。以国家重大工程“深中通道海底沉管隧道工程”为依托开展了系统研究。首先推导了火灾高温下钢壳混凝土结构瞬态温度场求解简化解析公式,然后在管节结构局部全尺寸火灾试验的基础上,拟合了工程尺度下钢壳-混凝土界面接触热阻值,并通过建立具有等效薄层结构的数值模型验证了理论求解的正确性,最后基于解析方法进行了温度场的计算与分析。综合3种方法分析得出以下结论:①基于理论解析公式对火灾试验结果的拟合,分析得到钢壳-混凝土界面接触热阻近似值为0.01 m^(2)·K·W^(-1);通过具有等效薄层结构的数值模拟结果与理论解析解的拟合分析,得到等效薄层结构的密度、比热容和导热系数分别为1.29 kg·m^(-3)、1005 J·(kg·K)^(-1)和0.1 W·(m·K)^(-1)。②通过理论解析方法,对火灾温度场进行了分析,分析结论与数值模拟、模型试验结果基本一致;火灾高温对钢壳-混凝土结构的影响深度主要在400 mm左右,400 mm以后结构温度增加不大。③由于钢壳和混凝土2种材料的导热性能不同,以及两者之间的界面接触热阻效应,致使钢壳与混凝土交界面处在火灾曲线的不同阶段出现温度突减和突增现象,并且整个管壁结构温度场在升温、恒温阶段及降温阶段前期出现“外高内低”现象,在降温阶段后期出现“外低内高”现象。提出的温度场分布规律为依托工程设计提供了依据;提出的界面接触热阻值确定及其等效模拟方法,可为类似工程计算分析提供参考借鉴。

The steel shell immersed tunnel is prone to strength degradation,structural bearing performance degradation,and unstable failure under high temperature of fire.Therefore,carrying out basic research on the temperature field distribution of the steel shell immersed tunnel structure under high temperature is necessary.In this study,systematic research was carried out based on the national major project"Shenzhong Link Submarine Immersed Tunnel".First,a simplified analytical formula for solving the transient temperature field of steel shell-concrete structure under high temperature was derived.Second,based on local full-scale fire tests of tube structure,the contact thermal resistance of the steel shell-concrete interface at the engineering scale was fitted.The accuracy of the theoretical solution was verified by establishing a numerical model with an equivalent thin layer structure.Finally,the temperature field was calculated and analyzed.The following conclusions can be drawn from the analysis of three methods.①Based on the fitting of theoretical analysis formulas to the fire test results,the approximate value of the contact thermal resistance of the steel shell-concrete interface is 0.01 m^(2)·K·W^(-1).The density,heat capacity,and thermal conductivity of the equivalent thin layer structure are 1.29 kg·m^(-3),1005 J·(kg·K)^(-1),and 0.1 W·(m·K)^(-1),respectively,according to the fitting analysis of the numerical simulation results with the equivalent thin layer structure and the theoretical analytical solution.②Through theoretical analysis methods,the fire temperature field was analyzed,and the analysis conclusion was basically consistent with the numerical simulation and model test results.The influence depth of fire high temperature on steel shell-concrete structure is primarily approximately 400 mm,and the temperature of the structure does not increase significantly after 400 mm.③Owing to the different thermal conductivities of the steel shell and concrete,as well as the interface contact thermal resistance effect between them,the temperature at the interface between the steel shell and concrete appears to suddenly decrease and increase at different stages of the fire curve.Moreover,the temperature field of the entire tube wall structure appears to be high outside and low inside during the heating,constant temperature,and early cooling stages,and low outside and high inside during the later cooling stage.The temperature field distribution law proposed in this study provides a basis for engineering design,and the determination and equivalent simulation method of interface contact thermal resistance may provide reference for similar engineering calculation and analysis.