Performance of concrete filled steel tube after exposure to fire with 100% granulated blast furnace slag fine aggregate infill concrete

The performance of concrete filled steel tubes (CFST) after exposure to fire was investigated in the present study. Granulated blast furnace (GBS) was used as fine aggregate in core concrete. The specimens were heated for 2 h at 200 °C, 400 °C, 600 °C and 800 °C. After which they were cooled to room temperature inside the furnace, and axial load was applied to the cooled specimens to check their behaviour after fire exposure. Different parameters such as heating temperatures, shape (circular and square), length (short and intermediate) and core configuration (CFST and concrete filled double-skin steel tube (CFDST)) were varied, and their effects were studied. A three-dimensional finite element model (3D-FEM) using ABAQUS software was predicted to simulate the behaviour of the tested specimens. The load-carrying capacity was insignificantly reduced for the specimens heated at 200 °C, 400 °C and 600 °C for both circular and square shape short and intermediate specimens. The load-carrying capacity of the CFST specimens was slightly higher than the CFDST specimens for all temperatures, shapes and lengths. The predicted 3D-FEM model could simulate the post-fire performance of the tested specimens with acceptable accuracy. For short specimens, local bulging and buckling deformed shapes and for intermediate specimens, global and Euler’s buckling deformed shapes were observed.