Effect of Transverse Reinforcement Configuration on Fire Resistance of Circular CFST Columns

The use of concrete-filled steel tubular (CFST) columns has grown increasingly in the construction industry. In the present study, the effects of the configuration of transverse rebars, either circular (CFSTC) or spiral (CFSTS), on the behavior of CFST columns under fire conditions were investigated. A finite element (FE) model capable of tracing fire-induced temperatures and axial deformations was verified using experimental data from fire tests on RC columns. The effects of various parameters on the fire behavior of CFST columns, including the compressive strength of concrete, the yield strengths of steel tube and reinforcing bars, the concrete cover thickness, the load ratio, the cross-sectional dimension, the longitudinal reinforcement ratio, the steel tube ratio, and the spacing of circular stirrups, were herein discussed and clarified. The effects of the investigated parameters were evaluated in terms of fire resistance time under sustained axial loading. Increasing the concrete compressive strength, reinforcing bar strength, cross-sectional dimension, and longitudinal reinforcement ratio generally increased the fire resistance time, whereas the effect of concrete cover thickness was comparatively small. For example, at a load ratio of 0.6, increasing the concrete compressive strength from 20 to 50 MPa increased the fire resistance time by 25.6% and 13.2% for CFSTC and CFSTS columns, respectively. Conversely, increasing the steel tube yield strength from 235 to 420 MPa reduced the corresponding fire resistance times by 46.3% and 37.4%, respectively. The relative performances of the transverse reinforcement configurations were also load-dependent; under the reference conditions, CFSTC exhibited approximately 4.0% higher fire resistance at a load ratio of 0.4, whereas CFSTS exhibited approximately 7.0% higher fire resistance at a load ratio of 0.6.