Behaviour of concrete filled steel stub columns during and after fire exposure

This paper investigates the behaviour of short concrete filled steel tubular (CFST) columns during and after fire exposure. A total of 10 circular CFST columns were loaded with different load ratios and heated to various temperatures for a specified fire exposure period. During the fire exposure phase, the temperature versus time curves of specimens were measured, and the strain developments of the steel and concrete in fire were measured by using photogrammetry method. The interaction between the steel tube and concrete was analysed accordingly. After the fire exposure, the specimens were cooled naturally in the furnace to room temperature and then the columns were compressed concentrically until failure. In the post-fire loading phase, the failure modes, load-bearing capacity and axial load-axial strain relationships were recorded and presented. The effects of temperature, initial load and hold time period of heating on the post-fire residual strength were discussed. A non-linear finite element (FE) model was developed to simulate the tests by using existing material models included the effect of fire exposure. The predictions indicate that the FE model can capture the post-fire residual strength of CFST columns reasonably, but improvement is required in predicting the post-peak response of the load-deformation curves.