Behavior Of Concrete-Filled Stiffened Square Steel Tubes Subjected To Eccentric Compressive Load

The concrete-filled square steel tubes have advantages of high bearing capacity, good ductility and toughness, convenient production and construction, great fire-resisted characteristics and economic effects, etc. In recent years it is a promising development structure that has been widespread concerned at home and abroad and increasingly used in many modern structures. However, If their width-to-thickness ratios of steel tube surpass a reasonable limit, local bucking is more likely to occur when they are subjected to eccentric compressive load, thus it reduces the bearing capacity of specimens. In order to improve the performance of such kind of composite columns, longitudinal stiffeners are welded on the steel tubes, which are called concrete-filled stiffened square steel tubes in this paper. Behaviour and mechanism of concrete-filled stiffened square steel stub columns were investigated in this paper including experimental and theoretical studies. Through the parametric analysis, the practical calculation methods for pure bending and eccentric compressive load-bearing capacity were developed. The research work is summarized as follows:1. The research on concrete-filled stiffened square steel tubes at home and abroad was reviewed firstly. The finite element method and test program were selected for the behaviour analysis of concrete-filled stiffened square steel tubes subjected to eccentric compressive load.2. A total of twelve concrete-filled square steel tubes were tested under eccentric compressive load, in which six specimens had stiffeners. The primary parameters in the tests were tube slenderness ratio and eccentricity ratio, And the phenomena and data of the tests were analysed in detail.3. Load-deformation relationship curves of concrete-filled stiffened square steel tubes subjected to eccentric compression were analyzed by finite element software ABAQUS. Considering initial defect and welding residual stress on the impact of specimens, and the numerical results are compared with the experimental results. The calculated results were in good agreement with experimental data, the reliability of finite element model was verified.4. Work mechanism on the composite columns was analyzed at seven aspects: deformation situation, load-deformation relationship curves, vertical stress distributions of steel tube and core concrete, interactions between steel and concrete, initial defect and welding residual stress impacting on the specimens as well as stiffened width impacting on the bearing capacity and ductility. It is then compared with mechanism of unstiffened concrete-filled square steel tubes.5. Based on the analysis of parameters, the practical calculation methods for pure bending and eccentric compressive load-bearing capacity of concrete-filled stiffened square steel stub columns was developed, taking into account impact on the specimens for initial defect and welding residual stress. The predicted results were in good agreement with those of tests. The research work can supply design of practical engineering with the value reference.