Study On Effects Of Initial Stress Tubes On Behaviors Of Concrete-filled Square Tubes

Concrete-filled steel tubular (CFST) members are steel tubes filled with concrete. CFST has been widely used in the past decades. In practice, hollow steel tubes are fixed firstly, and then concrete in steel tubes is casted. So, the initial stress for concrete-filled steel tube in practice always exists in steel tube. The initial stress do have influence on behaviors of concrete-filled tubes.In order to investigate its mechanical behavior, an experimental study on 14 square CFST members with and without initial stress in steel tube was conducted. After carefully analyzing the test data, it is found that slenderness ratio, the changing steel ratio, strength of the steel and the concrete, load eccentricity ratio as well as initial stress coefficient on the bearing capacity of the members have influence on load carrying capacity for concrete filled square tubes.Based on the experiments, the large commercial FEA software ANSYS was used to analyze these experiments. The calcuted results by ANSYS software are in good agreement with test ones, which made the following model parameters analysis possible and reliable. The mechanical behavior of the tube was studied by varying the slenderness ratio, the changing steel ratio, strength of the steel and the concrete, load eccentricity ratio as well as initial stress coefficient on the bearing capacity of the members. A kind of simplified model was suggested on the bearing capacity calculation of square CFST columns with initial stress effects considered .