Numerical Study on Reserve Fire Resistance of Continuous Steel Columns in Buildings

A simple design method typically applies a Fire Resistance Rating (FRR) to structural components in isolation based on their performance in the fire test. This approach naturally assumes that the interaction between these components does not degrade their fire performance. To assess the reliability of this assumption, this paper numerically investigated the fire performance of continuous steel columns, incorporating the effects coming from connected steel beams and composite slabs. A 3-step numerical validation, using ABAQUS and following a recommended general simulation process, confirmed the numerical model's accuracy for this research through agreement with experimental tests. The simulation results founded that the well-designed interior column subassemblage, T4-90, failed to reach the designed FRR. This is due to compression coming from the continuous bending beam through the beam bottom flange, significantly weakening the column performance. Rib stiffeners between column flanges are proposed to enhance resistance to contact forces from beam flanges during severe fires. However, the simulation found that the steel columns with rib stiffeners might fail immediately after reaching the FRR. Thus, this research introduced the concept of 'reserve fire resistance' (authentic fire resistance to FRR) to evaluate structural steel elements' resilience to fires exceeding the specified FRR, aligning with the concept of reserve capacity of structural resilience to earthquakes. Based on this concept, new limiting temperature design equations were proposed and validated for steel columns derived from their performance, which yielded an average reserve fire resistance of 1.30 herein.