Fire behaviour of axially loaded high-strength concrete-filled circular high-strength steel tubular columns

High-strength concrete-filled high-strength steel tubular (high-strength CFST for short) columns, characterized by the high-strength materials, exhibit fire performance distinct from that of normal-strength concrete-filled steel tubular (normal-strength CFST for short) columns due to the more critical material degradation at high temperatures. However, existing fire research and evaluation methods primarily focus on the normal-strength CFST columns, leaving a gap in understanding the fire behaviour of high-strength CFST columns. To address the deficiency of this area, a series of ISO 834 standard fire tests were conducted on four slender high-strength CFST columns and one slender normal-strength CFST column under axial load. During the experiments, the temperatures and deformations of the specimens were meticulously recorded. The results reveal a significant influence of load ratio on the fire resistance of high-strength CFST columns and the fact that the high-strength CFST column exhibits a shorter fire resistance compared to the normal-strength CFST column under the same load ratio. A finite element (FE) model integrating temperature field and mechanical analysis with the sequentially coupled approach was developed using ABAQUS and validated against the experimental data. Subsequently, the parametric investigation was performed to explore a wider range of high-strength CFST column parameters. A simplified method was proposed to estimate the load capacities of high-strength CFST columns subjected to fire.