Assessing the fire resistance of damaged <scp>reinforced concrete</scp> frames: A comparative study between <scp>2D</scp> and <scp>3D</scp> frames

Abstract Post‐earthquake fires pose a significant threat to urban environments, with potentially catastrophic consequences for buildings and infrastructure. To enhance understanding and mitigate these risks, this study conducts a comparative analysis of post‐earthquake fire (PEF) in two‐dimensional (2D) and three‐dimensional (3D) reinforced concrete (RC) frames using numerical simulations in SAFIR. Two‐hundred three‐bay RC frames, encompassing two‐floor and six‐floor configurations, were designed to represent a typical building stock constructed without specific seismic design considerations. The analyses considered varying levels of seismic damage and fire scenarios to evaluate structural performance comprehensively. Results reveal that seismic damage significantly reduces the time of collapse of the frames, compromising their structural integrity under PEF conditions. The 2D models consistently result in lower times until collapse for two‐floor frames compared to their 3D counterparts. For six‐floor frames, in the specific scenario of severe damage combined with severe fire, the 3D models can lead to slightly lower times of collapse; however, for all other damage and fire configurations, the 2D models consistently led to lower results. Overall, this study suggests that 2D models can be effectively utilized for certain assessments, particularly when a conservative approach is desirable.