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

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.