CALCULATION METHODS FOR TEMPERATURE FIELD AND FIRE RESISTANCE CAPACITY OF CIRCULAR CONCRET-FILLED STEEL TUBULAR COLUMNS

Based on experimentally validated finite element heat transfer models, extensive parametric analysis was conducted on the temperature field of fire-protected concrete-filled steel tubular (CFST) columns. The results show that the thermal resistance of fire protection, the steel tube thickness, and the column diameter influence the temperatures of the CFST. After 3 hours of standard heating, the temperature of the concrete at a depth of more than 150 mm remains below 300°C. When the CFST columns reach their fire resistance, the steel tube temperature generally exceeds 600°C. Calculations of radial deformation at this time reveal that separation occurs between the steel tube and concrete, thus the restraint effect of the steel tube on the concrete can be neglected when calculating fire resistance load-bearing capacity. Based on the results of the parametric analysis, a simplified calculation method for the temperature field of the circular CFST columns is proposed, which aligns well with experimental results. By disregarding the constraining effect of the steel tube, a simplified calculation method for the fire resistance load-bearing capacity of CFST columns was proposed and experimentally validated. The calculation results have an error of only 1.33% compared to the experimental results, and also align well with existing experimental results, proving the reliability of this simplified calculation method.