Study On Residual Bearing Capacity Of Urban Underground Highway Tunnel After Fire

With the rapid development of urbanization worldwide,the problem of urban traffic congestion is getting worse.In order to solve this problem,human beings began to vigorously develop underground space.As an underground traffic passage,road tunnels can effectively alleviate the traffic pressure on the ground space.With the development and widespread application of road tunnels,the problem of tunnel fires caused by flammable and explosive materials such as car accidents has become increasingly prominent.Researchers at home and abroad have found through a large number of tunnel fires that the damage of the tunnel structure caused by high temperature of fire will greatly reduce the bearing capacity and safety performance of the tunnel structure.In this paper,the temperature field analysis of the tunnel structure is carried out by ABAQUS finite element software,and the residual bearing capacity of the tunnel structure after fire is calculated based on the damage of material properties after fire.Furthermore,the effect of residual bearing capacity of tunnel structure under fire protection measures is analyzed.The main research contents of this paper include:(1)Temperature field analysis of tunnel structure.The theories mainly include thermal radiation,thermal convection,and thermal conduction.The reasonable assumptions based on previous studies is made.The relevant temperature field analysis parameters,including concrete density,thermal conductivity,specific heat capacity,was selected.The tunnel model is established by using ABAQUS finite element simulation software to analyze the variation of temperature field of tunnel structure under HC heating curve.The variation law of the depth of the section damage is studied by the isotherm of 300 °C,and the damage depth of the section increases with the increase of fire time as a power function.(2)On the basis of temperature field analysis,this paper considers the damage of material properties after different temperatures,and analyzes the advantages and disadvantages of different methods for calculating residual bearing capacity.The elastic modulus of the damage area of the concrete section was calculated by the slice-integral method,which is equivalent to the cross-sectional area of concrete at normal temperature.According to the force form of the rectangular tunnel section,the elastic constraint load-structure method is proposed based on the spring load-structure method.The reduction model of the tunnel structure after different fire time is established,and the deflection deformation under different loads is analyzed.The residual bearing capacity of the tunnel structure is calculated according to the deflection deformation,and it is concluded that the remaining bearing capacity decreases in the form of a double exponential decay function as the fire time increases.The internal force value of the concrete structure under different residual bearing capacity is further analyzed.(3)This paper investigates and summarizes the common fire protection measures for tunnel structures.The advantages and disadvantages of each fire protection measure is analyzed.The finite element model is established and temperature field is analyzed for two fire protection measures of spray fireproof coating and paste fireproof board.And the residual bearing capacity of the tunnel structure decreases as an inverse function as the damage depth of the section increases.Both fire protection measures have a good fire protection effect on the tunnel structure.The bearing capacity is not damaged with in 180 min of the fire.The fireproof board forming a cavity layer on the surface of the tunnel structure has better fireproof protection effect than spraying the fireproof paint directly on the tunnel surface.