Research Of The Concrete-Filled Steel Tube Structure

The concrete-filled steel tube (CFST) structure is a kind of composite structures, evolved and developed on the basis of steel reinforced concrete structure, spiral reinforced concrete structure and steel structure. Because of synergy of the two materials, the structure remedies their defects respectively and excellently improves its ductility and plasticity. With many unique advantages, the structure is widely applied to the constructional engineering.According to the characteristics of CFST structure and the problems which remain in practice, the article researches the CFST structure in four aspects, the constraining coefficient, the formula for calculating the ultimate capacity of the CFST short column, the bearing behavior of mid-long column subjected to axial pressure and the anti-seismic behavior of CFST frame. The research achievement can be used as guidance for engineering design & practice.In the researching for the constraining coefficient about CFST, firstly, the raising coefficient of core concrete strength is analyzed. The relation between the constraining coefficient and the raising coefficient is established. According the relation, the effective range of the constraining coefficient is obtained, in which the lateral deformation of the core concrete can be effectively confined. The relation between the raising value of strength and the constraining coefficient is also determined.Based on the forth strength principle, the limit bearing capacity of the CFST short column subjected to axial pressure is analyzed, the formula for calculating the steel stress in plastic stage and the strength criterion of concrete under triaxial loading conditions have been established. According to the analysis of theoretical study, the limit bearing capacity formula of the CFST short column subjected to axial pressure is found. On the basis of the theoretical analysis, axial bearing components with four kinds of constraining coefficients are experimented. The theoretical values are in good accordance with experimental ones. By analyse of the components, it is shown that thelimit-bearing of the components can be divided into two stages, and calculating formulas of two stage are also recommended. The calculating formulas can be used to instruct parasitical engineering.The paper introduces two methods of calculating the limit bearing capacity of CFST mid-long column subjected to axial pressure, one is the tangent modulus and the other is the integration tangent modulus. The reaction between steel tube and core concrete is fully considered. On the basis of the theoretical analysis, fourteen samples with five kinds of long diameter ratio are studied experimentally. The testing conclusion accords well with the theoretical result, which is shown that the formula is fit for calculating the stable bearing capacity of mid-long column. When other conditions are same, the stable bearing capacity of CFST mid-long column is not reduced evidently along with the long diameter ratio increased. In the range of testing ratio, a stable coefficient is introduced which can be used for calculating the stable bearing capacity.Through the experiment with the two CFST frame structures under reversed loads, which have the same shapes, materials and dimensions, several parameters, such as stiffness, limit load, energy consume ability, were studied. By applying the extreme principle, the behavior of CFST frame structure is analyzed. Firstly, a collapse pattern of the structure is founded which is in good accordance with the experimental results, then the formula for calculating the load-bearing of the structure is established. The stiffness, limit load and energy consume ability of the frame are studied, and the calculating methods of the stiffness is brought forward. From the contrast research, the CFST frame structures has many advantages, such as higher initial stiffness, higher load-bearing, good anti-seismic behavior and so on. By comparing theoretical value with experimental results, the former is fit well with the latter. The research achievemen...