Axially Loaded of Concrete-Encased Concrete Filled Steel Tubular Stub Columns after Fire

In order to investigate the failure mechanism and structural performance of axially loaded concrete-encased concrete filled steel tubular (CFST) stub columns after fire exposure, the failure mode, axial compression ultimate bearing capacity and axial stiffness of concrete-encased CFST stub columns were analyzed based on experimental study and finite element model (FEM) simulation. A total of 8 concrete-encased CFST stub columns specimens with different cross-section types, steel tube dimension and slenderness ratios were tested after fire exposure, and the nonlinear FEM simulation was carried out by ABAQUS software. The results show that compressive failure modes are observed for concrete-encased CFST stub columns, which is similar to reinforced concrete stub columns. Compared to a specimen at ambient temperature, the drop of axial compression ultimate bearing capacity of concrete-encased CFST stub columns is about 27.4%-38.2%, and the drop of stiffness is about 61.4%-69.0%. When the fire exposure time and the size of the specimens are the same, and the thickness of the reinforced concrete cover improve to 1.53 times, the rate of decline of axial compression ultimate bearing capacity and axial stiffness for circular specimens are 8.4% and 1.3%, respectively, and for the square specimens, the rate of decline of axial compression ultimate bearing capacity and axial stiffness are 5.8% and 4.1%, respectively. Compared with the FEM simulation results, the mean and standard deviation of simplified method of calculation error are 4.9% and 5.3 for axial compression ultimate bearing capacity, the mean and standard deviation of axial stiffness calculation error are 13.8% and 9.8.