Full-Range Fire Behavior of Circular Tubed Reinforced Concrete Columns: A Finite Element Investigation

Circular tubed reinforced concrete (TRC) columns are increasingly used in high-rise and critical infrastructure because of their high load-carrying capacity and improved confinement characteristics. Although their performance under standard fire exposure has been studied to some extent, limited information is available on their behavior during the complete fire cycle, including both heating and cooling phases. This study presents a nonlinear finite element investigation of the full-range fire behavior of circular TRC columns.

A sequentially coupled thermal–structural analysis was carried out in ABAQUS. The thermal response of the column was first obtained under standard fire exposure, and the resulting temperature field was subsequently transferred to the structural model. Temperature-dependent material properties for steel and concrete were adopted according to Eurocode recommendations, while concrete damage plasticity was employed to represent stiffness and strength degradation at elevated temperatures. The numerical model was validated against available experimental results from the literature.

The analysis focused on temperature distribution, axial deformation, lateral deflection, residual load-carrying capacity, and failure characteristics during both the heating and cooling stages. The results show that significant structural degradation may continue during the cooling phase because of delayed heat penetration into the concrete core and progressive material deterioration. Circular TRC columns exhibited improved confinement and retained substantial residual capacity even after peak fire exposure. The study highlights the importance of considering the complete fire history rather than the heating phase alone when evaluating the fire resistance and post-fire safety of composite columns. The proposed numerical framework provides useful information for the performance-based fire assessment and design of circular TRC columns.