Analysis On The Mechanical Properties Of Concrete-filled Steel Tubes Stub Columns

This paper presents theoretical analysis deeply on the behavior of concrete-filled steel tubes (CFST) dumbbell shaped stub columns under axial compression and circular(square) CFST stub columns under local compression. The main research contents are as follows:(1) Applying unified formula for stress-strain relations of concrete under unixial load, the author used ABAQUS to establish the3D finite element model and to analyze the behavior of concrete-filled circular steel tubular (CFST) dumbbell shaped stub columns under axial compression. The elasto-plastic method was also used to analyze the load-deformation curve of CFST dumbbell shaped stub columns. The two analysis results are in good agreement with the experiment results from references. Analytical results by elasto-plastic method were slightly lower than that by finite element method. Then based on the two methods, the axial stress and perimeter stress of steel tube, the longitudinal and perimeter stress of steel web, the axial stress and radial stress of concrete core, and the longitudinal stress of concrete inside the steel web space in CFST dumbbell shaped stub columns were discussed. At yield state, the axial stress of section steel was slightly lower than its yield stress because of the confinement effect for concrete. The analytical stresses in CFST dumbbell shaped stub columns by the two methods were almost the same, and the finite element model could reflect that the longitudinal stress of the concrete inside the steel web space increases lightly for the concrete confined by steel webs. Based on the limit equilibrium method, simplified formula for the axially loaded CFST dumbbell shaped stub columns was proposed. The analysis results by limit equilibrium method are close to those by finite element method, and both are in safe range compared with the experiment results from references.(2) The author used ABAQUS to analyze the behavior of circular CFST stub columns under local compression, and discussed the influences of local compression area ratio, steel ratio, and strength of steel and concrete on local compression bearing-capacity of circular CFST stub columns. Based on the Fitting regression, useful and simplified formula for the local loaded circular CFST stub columns was proposed. and the calculation results are in good agreement with the experiment results from references.(3) The author used ABAQUS to analyze the behavior of square CFST stub columns under local compression, and discussed the influences of local compression area ratio, steel ratio, and strength of steel and concrete on local compression bearing-capacity of circular CFST stub columns. Based on the Fitting regression, useful and simplified formula for the local loaded square CFST stub columns was proposed. and the calculation results are in good agreement with the experiment results from references.