Mechanical Performance Of Recycled Concrete-Filled Circular Steel Tubular Structures

In this thesis, theoretical analysis on the performance of recycled concrete filled circular steel tubular (RCFST) structures is presented. The main contents are listed as follows:(1) Uniaxial compressive and tensile stress-strain relations of recycled concrete and tri-axial compressive and tensile stress-strain relations of laterally confined recycled concrete were proposed. Based on existing experimental results and the mechanical model of normal concrete, the unified calculation method of the mechanical performance of recycled concrete with different substitution rates was obtained. Based on tri-axial stress-strain relationship for normal concrete, the stress-strain relations of recycled concrete under tri-axial compression were proposed.(2) The elastic-plastic full-range analysis method for RCFST stub columns under axial compression was proposed, and the mechanical performance of RCFST stub columns under axial compression was illustrated. The practical calculation formula for axially loaded RCFST stub columns was established and the reduction relation between the bearing capacity of RCFST stub columns and that of CFST stub columns under axial loading was presented.Based on continuum mechanics and axial symmetric tri-axial compressive stress-strain relationship for recycled concrete, the mechanical model of concentric cylinder for circular RCFST stub columns was adopted and the elastic-plastic full-range analysis was conducted. Fortran was used for the calculation program. With the establishment of ABAQUS finite element models for axially loaded RCFST columns, the bearing capacity and load-deformation relationship of the specimens were calculated. Parametric analysis was conducted using elastic-plastic analysis method and the practical calculation formula for the stress-strain curves was presented. Compared with experimental results, the elastic-plastic analysis method and the practical calculation formulas were demonstrated reliable in predicting the load-deformation relationships. (3)Based on plane section assumption and tensile and compressive constitutive model for recycled concrete, fiber modeling method was applied to calculate the load-deformation relations of eccentrically loaded RCFST columns and middle-long RCFST columns under concentric loading, and the reduction relation between the eccentric bearing capacity of RCFST stub columns and that of CFST stub columns was presented.Based on elastic-plastic full-range analysis method, the numerical constitutive model for the recycled concrete filled steel tubes was determined. Plane section assumption was adopted and non-linear analysis on eccentrically loaded RCFST columns was conducted using both fiber modeling method and ABAQUS. Compared with experimental results, the fiber modeling method was demonstrated reliable in predicting the load-deflection relationships, and the influence of substitution rate on the eccentric bearing capacity of RCFST columns was discussed.