Analysis And Simulation System Of Steel Structures In Fire

Steel structure has developed rapidly in engineering for its unique advantage. With the enlargement of its application range, the non-fire-resistant defect of steel material has been taken people's more attention. Since 80s of 20th century, a series of researches have been carried out on the behavior of steel structure in fire around the world, while most of them are about steel members in heating path. In fact, the fire-resistant behavior of the global structure is greatly different with that of single member. Furthermore, different combinations of heating, cooling, loading, and unloading may be subjected to the steel structure during the burning process, so the researches basing on single path can not accurately reflect the actual behavior of steel structure in fire, it is necessary to study the behavior of the global structure in multi-path.Based on above reasons, the global steel structure is taken as the object and its behavior in different temperature-load paths is researched systematically in this paper, the detail works and corresponding conclusions are as follows:(1) Carrying out high-temperature material test using Q235Up to now, most of the high-temperature material tests are steady or transient tests, from which the material properties can be obtained, such as stress-strain curve on certain temperature, the variety regulation of initial elastic modulus, yield strength, ultimate strength changing with temperature, which are only related to temperature state. Different temperature-load paths were set in this paper, the continuous functions of stress-strain-temperature relation were obtained under different paths, studying the influence of temperature-load history on steel behavior.(2) Deriving stiffness matrix of fiber-beam elementUsing the constitutive relation obtained in this paper, adopting fiber-beam element, the stiffness equation suitable for high-temperature analysis of steel structure was derived by principle of virtual work. In deriving, the material nonlinearity and geometric nonlinearity were considered. According to the characteristic of fiber-beam element, the explicit form of element stiffness matrix was presented by further operation, so as the explicit forms of average strain increment and temperature load, which supply the basis for the follow-up analysis software of steel structure in fire.(3) Deriving stiffness matrix based on other sectionsBy using fiber-beam element, analysis can be carried out when the temperature distribution is asymmetrical along section height. Based on which, the element stiffness matrixes of other section shapes were also derived, making the analysis be possible when the temperature distribution is asymmetrical along both section height and width, so as the cases of circular, ringshaped, or fanshaped section.(4) Developing the finite element analysis software of steel structure in fireBased on theoretical analysis, the analysis software of steel structure in fire was developed. Constitutive relation functions of steel under different temperature-load paths can be inputted simultaneously. In computing, the path state can be judged by paths recognition module of the software, and then the corresponding functions was selected automatically. The heating-cooling stage must be included in the burning process at least once, and the alternation of loading and unloading may be caused by stress redistribution at elevated temperature. Automatic paths conversion can ensure the continuity of computation, which realizes dynamic tracking of the steel structure during the fire process. By comparing the results of the software with experimental data and ANSYS results, the analysis software developed in this paper was validated, and its application on fire protection design of steel structure was presented by several examples.