Cooling behavior and residual strength of post-fire concrete filled steel tubular columns

• A comprehensive computational study was performed to investigate the behavior of CFST columns after fire exposure.
• Different natural fire conditions were investigated based on the Cardington full-scale fire tests and FDS software.
• The proposed FEA model was applied to predict the load versus deformation relationships of CFST columns after uniform heating or ISO-834 fire exposure.
• Parametric analysis was performed to investigate the influence of fire duration time, cross-sectional diameter, slenderness ratio, yield stress of steel and concrete cubic compressive strength after natural fire exposure.
• A simplified approach to evaluate residual load capacity of CFST columns was proposed. Strength reduction of steel and concrete is considered as a function of the maximum temperatures, obtained from the whole fire exposure process.

An interaction approach to evaluate the residual strength of concrete filled steel tubular (CFST) columns after fire conditions is developed. The approach is based on strength reduction of steel tube and concrete as a function of the maximum temperature, which is obtained from the whole fire exposure process. Sixty-one CFST column tests to the residual strength of specimens subjected to uniform heating or ISO-834 standard fire were employed to benchmark the proposed approach. The predictions showed good agreement compared with experimental data. In order to obtain the post-fire load versus deformation relationships, a 3D finite element model was developed to investigate the behavior of CFST columns under different heating conditions. Based on the natural fire curve from Cardington fire tests and Fire Dynamics Simulator (FDS) software, parametric studies were performed to investigate the effects of parameters to the heating and post-fire behavior of CFST columns under natural fire conditions. From the theoretical and computational analysis, it can be concluded that the residual strength of CFST columns after natural fire exposure is generally affected by fire duration time, cross-sectional diameter and slenderness ratio.