Seismic behavior of fire-exposed concrete-filled steel tubular (CFST) columns

The seismic behavior of fire-exposed concrete-filled steel tubular (CFST) columns was investigated based on a verified finite element analysis (FEA) model in this paper. Coupling effects of the fire exposure and sustained axial load on CFST columns were considered. Existing test data was employed to verify the feasibility of the model, where the temperature field tests, fire resistance tests, cyclic tests of CFST columns under ambient temperature and cyclic tests of CFST columns after fire exposure without coupling effects were considered. Further analysis was carried out based on the verified model. It was found that the coupling effects of fire exposure and sustained axial load could cause structural failure of CFST columns during fire exposure. However, if the CFST columns did not fail due to coupling effects, the residual deformation, residual stress, hysterical curves, and ultimate strengths after fire were similar to the CFST columns subjected to fire and axial load sequentially. The interactions between steel tube and concrete were studied. It was shown that the bond strength did not influence the behavior of CFST columns under and after fire exposure significantly. On the other hand, the contact stress was influenced by the lateral deflection and fire duration time of CFST columns. The deformation curves of CFST columns with low shear span ratios after fire exposure were generally similar to those without fire exposure. Lastly, it was found that the strength degradation of CFST columns with lower shear span ratios was more significant after fire exposure.