Study On Temperature Field And Mechanical Properties Of Large Space Steel Truss Under Fire

Fire is one of the major disasters that cause loss of people’s life and property.As the mechanical properties of steel decrease significantly with the increase of temperature,the safety performance of steel structure under fire is always an important topic in the field of disaster prevention and mitigation.Owing to its advantages of good overall mechanical performance,high stability,open internal space and beautiful appearance,large space steel truss structure is widely used in large space structures such as railway waiting hall,large exhibition hall,industrial plant and other buildings.However,due to the difference of fire temperature field distribution of large space steel structures,the complexity of mechanical response of components,the uncertainty of the determination standard of structural fire resistance limit and the critical temperature of fire retardant coating protection,the research on the fire resistance analysis method of large space steel structures is not perfect at home and abroad.Taking the layout plan of a high-speed railway station waiting hall as a reference,this paper establishes a large space steel truss roof structure system,and takes it as research object,to study the distribution law of the air temperature field in large space fire,the calculation method of the structure temperature field and the mechanical properties of the structure under fire temperature field.The main research contents are as follows:(1)Simulation study of air temperature field in large space fireAppropriate turbulence model,combustion model,fire source model and radiation model are selected to simulate the air temperature field of large space local fire using FDS field model,so as to explore the variation law of air temperature with time and space position in large space local single point fire.Compared with the calculation results of domestic and foreign empirical formulas,the reliability of FDS simulation is verified and the reasons for the difference are analyzed.The influence of space size on fire temperature field is studied.(2)Study on calculating method of temperature rise of steel member under fireBased on the basic principle of heat transfer and the principle of adiabatic surface temperature(AST),the calculation method of temperature rise of steel members under fire is studied.The calculation of structure temperature according to the temperature of smoke in the standard ignores the influence of flame radiation,while the AST principle makes up for this deficiency.The transformation from air temperature field to structure temperature field under fire is realized by MATLAB programming.In a specific fire scene,the two methods are used to calculate fire temperature rise of components at different positions in the structure.By comparing the result differences,the different application ranges of the two methods are summarized.(3)Study on mechanical properties of large space steel truss under fireBased on the normal temperature design of the large space steel truss of the waiting hall of a virtual high-speed railway station building,the mechanical properties of the steel truss structure under fire are studied.The critical temperature method and bearing capacity method in the standard are used for possible overall and local fire scenes in the building.The variation of the internal force,displacement,stress and strain of the structure(components)with temperature and the displacement characteristics at failure of the structure are compared under different fire scenes and temperature fields.(4)Study on practical fire resistance design methods of large space steel trussBased on the research results of air temperature field under large space fire,structural temperature field and structural mechanical response,the practical fire resistance design methods of large space steel truss,which shall couple fire temperature field calculation and structural mechanical response analysis are summarized.The methods include the calculation of air temperature field and structural temperature field,the connection of fire simulation software FDS and structural finite element software ABAQUS,the mechanical property analysis of the structure which connects heat transfer calculation and explicit dynamic calculation,the fire resistance limit determination criteria and protection range of large space steel truss under fire,etc.