Nonlinear Finite Element Analysis Of Portal Frame Structure Under Fire

The steel structures are widely used in modern building structures due to its advantage properties such as high strength, light weight and so on. The poor fire-resistance ability is the main weakness of steel structure in that its mechanical property such as strength and elastic modulus decrease severely in high temperature. When fire occurs, severe damage or global collapse will happen to the steel structure. Therefore, it is very important in the theory and practice to study the problem of fire resistance and fire protection of the steel structures.In china, test-based design method is the traditional fire resistance design method for steel structures. However, using the test-based fire-resistance design method, it is hard to simulate the magnitude and distribution of load and the end restriction conditions of the specimen in the structure. The fire-resistance measures of steel structure can be determined through calculation-based fire-resistance design method. Therefore, a thorough study of the calculation-based fire-resistance design method has great theoretical significance and practical value.After consulting the home and overseas existing research results, this dissertation contrasts and analyzes the steel's material property under the high temperature in the fire, obtains the computing mode of the material property (yield strength and elastic modulus) fit for the fire-resistance design of the steel structure.Based on the research dynamic condition of fire-resistance for steel structure in domestic and international, according to the classical theory of calorific and the finite element analysis theory, This paper aims to provide the real ability of resisting fire of portal steel frame under practical fire condition. The transient heat transfer is calculated, whereas the whole-process response of portal frame exposed to fire is calculated with double nonlinear finite element technique. An advanced thermal and mechanical simulation techniques is adopted to assess the performance of frame structures under fire conditions with the finite element program ANSYS. The paper examines the time of resistance to fire and limited temperature on structure, judges weak in structure of resistance to fire and get the deformation of the structure. Therefore, the analysis can illustrate the real performance of the structure in fire.The researched results in this article have the certain guiding sense and the reference value to the structure system limiting condition research under the real fire function as well as the fire-resistance design method of steel structure construction.