Research on the collapse mechanism and path of the steel frame structure under fire

To study the collapse mechanism of steel frame structures in a realistic fire scenario, a 5-story steel frame structure with floor slabs is selected as the research object. A thermal-mechanical coupling model of the steel frame structure, employing beam and shell elements, is established by the finite element software ABAQUS. A design fire scenario is created and the fire dynamics simulation is performed by the FDS to simulate fire process, so as to obtain the temperature curve throughout the fire. Based on the finite element simulation, the failure modes, deformation-time curves of column members, internal force-time curves of beams and columns, and critical temperatures of the steel frame structure under different fire conditions are investigated. Furthermore, the influence of beamcolumn stiffness ratio, beam-column bending moment ratio, and fireproof coating thickness on the fire response of the steel frame structure is explored through parameter analysis. The results indicate that the highest temperature obtained from the temperature curve calculated in FDS exceeds that of the ISO-834 standard fire curve. Therefore, relying solely on the ISO-834 standard fire curve in fire resistance design may lead to unsafe outcomes. Except for the top floor, the collapse process of rooms at the same location on different floors exhibits similarities in case of fire. The critical temperature for the failure of components in models without fireproof coating has been determined to be above 730°C, whereas in models with fireproof coating, it is found to be above 550°C. Finally, the collapse path of the steel frame structure under fire is proposed based on the process of internal force redistribution.