Research On Shear And Torsion Behavior Of Concrete Filled Steel Tubular Members And The Application In National Standard

Concrete-filled steel tube(CFST) can comprehensive use steel tube which has high tensile strength and concrete which has high compressive strength. In the loading process, the steel and concrete will interact, and thus the combined performance is not the simple sum of steel and concrete. CFST will showing excellent mechanical properties, for example: high strength, good ductility, because of the confinement effect.Currently, the major achievement on CFST are based on the "unified theory ". With this theory, this paper does the research on the following aspects:Firstly, the theoretical research of torsion stiffness of CFST.Currently, there is no good method on calculating the shear modulus and torsion stiffness of CFST. The existing formulas that were get by regression analysis are very complex and there is no theoretical basis. Therefore, this thesis make a deep study of the shear modulus and torsion stiffness. Analyzing the process of twisting theoretically. The process of torsion is divided into three stages. Using classical elasticity theory for elastic section, the fitting method with parabola for ela-plastic section, the equivalent space truss model for plastic section, then obtained the theoretical formula of equivalent torsion stiffness and shear modulus.Secondly, verifying the torsion stiffness with FEM method. Then the theoretical formulas were verified by finite element method, analyzing the effects of the steel ratio, steel grade, concrete grade and the empty ratio. After the modification of the formula, the calculated results agree well with the software simulation results.Third, the theoretical research of torsion and shear strength of CFST.Then analyzing the shear and torsion properties of CFST. A theoretical formula and practical formula on shear strength of CFST is given; A new idea on shear and torsion capacity of hollow CFST is put forward, which makes the solution simplifying greatly.Forth, the research of Technical Specification of Solid and Hollow Concrete-Filled Steel Tubular Structures .On the basis of "Technical Specification of Hollow -Concrete-Filled Steel Tubular Structures", make some recommendations for solid and hollow concrete-filled steel tube. Including:1) In axial compression, through the theoretical analysis and finite element method, correct the confining factor, making the formula is also suitable for elliptical concrete-filled steel tube and the sand concrete-filled steel tube, so that the formula applied more widely. Then, by a large number of calculations, finding that the thickness of steel pipe has little impact on the characteristic index of CFST. So we can neglect the effects of steel thickness for the performance of concrete-filled steel tube and replace it with the average, which will bring a small mistake;2) On stable, analyzing the relationship between CFST and initial defects with Koiter's theory, verifying that the empty steel tube is very sensitive to local defects, while is not sensitive to local defects after be formed, then simplify the stability factor formula to make it more reasonable.3) The latest research results in other areas of CFST are included.