Nonlinear Finite Element Analysis Of Steel Frame Girder In Fire

The poor fire-resistance ability is the main weakness of steel structure in that itsmechanical property such as strength and elastic modulus decrease severely in hightemperature. When t fire occurs, severe damage or global collapse will happen to thesteel structure. In china, test-based fire resistance design method is the prevailing fireresistance design method for steel structures. However, using the test-based fireresistance design method, it is hard to simulate the magnitude and distribution of loadsand the end restriction conditions of the specimens in the structure. The ultimate fireresistance of the steel structure and the fire protection measures can be determinedthrough calculation-based fire resistance design method. Therefore, a thorough study ofthe calculation-based fire resistance design method has great theoretical significanceand practical value. In this paper, based on the problems on the fire safety design of steel structures,the following researches have been accomplished. Considering the effects of static loadand thermal stresses, eigenvalue buckling analysis is applied to the I-section girder inthe steel frames based on the finite element method, and the girder's buckling modes inthe fire are determined; On the basis of the eigenvalue buckling analysis, consideringthe material nolinearities and geometical nolinearities, nolinear buckling analysis isapplied to the girder in fire. This paper also checks the effects of the various factors ofthe girder's limited temperature and fire-resisting time. These factors include restrictionconditions, the magnitude of load, initial imperfections and the catenary force due tothe increasement of the girder's deflection. Based on the heat transfer principium,thermal-structure coupled analysis of plane frame stucture has been carried out and theweakness of the steel frame in the fire has been determined. The influence betweenmembers exposed to fire and members isolated from fire are also checked in this paper.Therefore, the thermal-structure coupled analysis can illustrate the real performance ofthe structure in fire.