Research On Reinforced Concrete Filled Steel Tubes Under Bending And Tension And Complex Stress Condition Based On Unified Theory

The reinforced concrete filled steel tube not only has characteristics of high bearing capacity, high stiffness and good ductility, but also can overcome drawbacks of common concrete filled steel tube, such as larger wall thickness and poor fire resistance. And it has been gradually applied in the project. As a new type of composite component, it has a complex working mechanism and lacks of systematic study on mechanical property and connecting structure. In this paper, we select the concrete filled steel tube with inner steel pipe, rebar and section steel as study objects, explore the correlativity of flexural bearing capacity and complex stress, as well as the jointly work performance of inside and outside steel members with a tensile effect, so as to obtain the design value of bearing capacity with simple form and scientific value.Study the flexural bearing capacity under limit conditions. The paper is conducted to discusses the position of neutral axis through solving the balance equation of components under pure bending at limit conditions, bring in the position of neutral axis to moment equilibrium equation, and obtain the theoretical value of ultimate flexural bearing capacity for the reinforced concrete filled steel tube with inner stiffener. At the same time, the paper establishes the bending model with pure bending effect by the finite element software ABAQUS to verify the accuracy of theoretical solution. Moreover, the norm value of flexural bearing capacity for special concrete filled steel tube is verified and modified by the theoretical value and finite element value, and then the norm value is modified through 3 groups of pure bending test experiments for 18 reinforced concrete filled steel tubes.The interactive equation under complex stress conditio n is conducted. Based on the limit equilibrium theory, the reinforced concrete filled steel tube is considered that it is comprised of three component: the outer steel tubes, the inner reinforced member and the concrete. However, the balance equation of the three party is not considered while the equilibrium equation of compress, bending, shear force and torsion. The model is equivalent to a space truss model, which is composed of an equivalent pressure member bar, a concrete diagonal bar and a steel tensile rod. The interactive equation after eliminating the internal force is obtained.Study on the common working performance of non-uniform total cross section of the internal and external components. The bond test of steel tube under tension and compression is conducted to obtain the ultimate bond stress and its influencing factors, so as to make clear failure mechanism and process. According to the existing bond force theory and test results, as well as considering the bond effect between inner stiffener and concrete, the thesis obtains the design values of tension bearing capacity for non-uniform total cross section. Then the connection mode between tower test of concrete filled steel tubes with inner stiffener and inside and outside steel member is preliminarily designed, and finite element numerical simulation of the test to get the stress ratio of inside and outside steel member is carried on, as well as whether the tension member meets bearing capacity requirements is verified, the difference of common working capacity for inner rebar and section steel plans is analyzed and compared.