Post fire behavior of square and rectangular concrete filled steel tubes with granulated blast furnace slag fine aggregate concrete

The present study investigated the behavior of concrete-filled steel tubes (CFST) and concrete-filled double-skin steel tubes (CFDST) of square and rectangular shapes after exposure to elevated temperatures. The infill concrete was prepared with granulated blast furnace slag (GBS) as fine aggregate, and no natural fine aggregate was used. A total of 20 CFST and CFDST specimens of both square and rectangular shapes were prepared. The specimens were heated at 200, 400, 600, and 800 degrees C temperatures for 2 h and allowed to cool inside the furnace after heating. Axial load was applied to the specimens to check their behavior after exposure to fire. The reduction in the load-carrying capacity was insignificant for the specimens heated at 200, 400, and 600 degrees C for both square and rectangular CFST and CFDST conditions. The decrease in load-carrying capacity was slightly higher in the case of CFDST specimens compared to CFST specimens. A three-dimensional finite element model using ABAQUS software was proposed for predicting the behavior of the tested specimens. The proposed model could predict the behavior of both unheated and heated specimens with acceptable accuracy.