Finite element analysis of the fire-resistance capacity of steel frame girders

In order to thoroughly understand the ultimate state and the effect of various factors on load capacity of the steel frame girder in fire, the finite element analysis of the ultimate load capacity of the I-section steel frame girder in fire subjected to different loads and restrictions, and thermal-structure coupling analysis of plane steel frame are performed. The results show that lower flange lateral twisting is the failure mode of the steel frame girder in fire. The effect of initial geometric imperfections on the limit temperature of both rigidly connected and simply supported I-section girder is limited. The catenary force due to the increment of the girder's deflection and the local buckling of the rigidly connected girder can counteract the thermal stress. Under higher loads, the limit temperature and fire-resisting time of the rigidly connected girder are higher than that of the simply supported girder. The influence of the load on the limit temperature and fire-resisting time of the rigidly connected girder is less than that on the simply supported girders. The joint is the weakest area of steel frame for fire-resistant. Change of internal forces of the unfired components is obvious after fire occuring.