| Fire is one of the most frequent disasters and will cause great loss.With the development of society,the level of science and technology is also gradually improving,people have a higher demand for expanding the building space and improving the bearing capacity of the structure.As the building structure tends to be complicated and high-rise,the bearing capacity of structure and components is increasingly required.Concrete-filled steel tube column has great advantages in this aspect and its application is also more and more extensive.Therefore,its fire resistance performance is becoming more and more important.Concrete-filled steel tube structure is a new type of structure between steel structure and reinforced concrete structure.In the process of stress,the interaction between steel tube and concrete forces each other,to make up for their shortcomings,give full play to the advantages of both.Under the action of fire,with the increase of temperature,the bearing capacity and fire resistance limit of concrete-filled steel tube members decrease gradually.It is the key to study the reliability of fire behavior of concrete-filled steel tube structures to determine the change of material properties and fire resistance of concrete-filled steel tube members under the action of high temperature.In this paper,the deterministic numerical simulation analysis and the randomness numerical simulation analysis considering the dispersion of main influencing factors are carried out for the fire resistance limit of circular steel tubular concrete column,and the regularity and randomness of the fire resistance limit are preliminarily studied.The main research ideas include the following parts:(1)The properties of steel and concrete in CFST structures at high temperature are summarized,including thermal properties and mechanical properties.The stress-strain relationship between concrete and steel at high temperature is discussed.(2)The random laws and distribution types of major influencing factors such as material performance,geometric parameters,permanent load and variable load were studied,and their statistical parameters were determined by referring to relevant literature.The main probability models of fire occurrence,statistical results of fire load density and typical fire heating curves are discussed.ISO834 standard heating curve is adopted as heating curve for numerical simulation.(3)Based on the stress-strain relationship of steel and concrete at high temperature,the basic assumption of fire resistance analysis is given.The basic theory of fire resistance analysis of concrete-filled steel tube(CFST)column is briefly introduced.Based on the existing research results,the deterministic analysis program of section temperature field and fire resistance limit is compiled.The simulation results are compared with the experimental results of other scholars.Taking a concrete concrete-filled steel tube column in a certain project as the analysis condition,its material performance,geometric parameters and load bearing value are determined according to the code,and its fire resistance limit is analyzed.(4)By using the multiplicative congruence method and inverse function method,as well as the statistical parameters and distribution types of the main influencing factors,a large number of random values of each random variable of concrete-filled steel tube column under fire are obtained,which are tested and compared to analyze whether they conform to their respective distribution types.By using the Monte-Carlo method,the randomness analysis program of the fire resistance limit of CFST column with the main influencing factors considered was compiled,and the randomness of the fire resistance limit was preliminarily studied. |
