Static Behavior Of Recycled Aggregate Concrete Filled Steel Tubular Stub Columns Under Axial Compressive Loading

With the fast city development in the world, waste concrete takes the largest proportion (30%~40%) of construction and demoliton waste which generates the problem of enviromental pollution and increases charges for landfilling. Recycled aggregate concrete (RAC) produced with waste concrete working as recycled aggregate provides a possibility to recycle the structural garbage, which has a promising future as ?green building'solution to save our natural resources and protect our living environment. Up to date, the RAC is mainly used as non-structural concrete due to its poor ultimate capacity and low elastic modulus. Concrete-filled steel tube (CFST) with high load bearing capacity, good ductility performance and excellent dynamic behavior generates the idea of filling the RAC into the steel tube, which makes it possible to use RAC as the main load bearing members for multi-level structures. As a new type of structural member, the mechanical behavior of recycled aggregate filled steel tube (RACFST) has not been fully understood. In this thesis, experimental and theoretical analysis have been carried out for the RACFST stub columns under axial compressive loading.As part of this work, the experiments for the 18 RACFST and 6 CFST stub columns under axial compressive loading were concducted to investigate the vertical load versus vertical deformation (horizontal deformation) relationship and the failure modes of the speimens. Different RAC strength, recycled coarse aggregate (RCA) replacement percentage, steel strength and ratio of steel area over concrete area were considered in the experiments to evaluate how these parameters influenced the ultimate response of RACFST specimens.The longitudinal and horizontal strains in the steel tube were experimentally measured. The stress versus strain relationship of the steel tube was obtained by numerical programming based on the assumption that the steel tube was under plane stress state. Cross sectional analysis was then conducted to obtain the stress-strain relationship of the RAC core. The confinement effects from the steel tube and the conctribution of the RAC core and the steel tube to the ultimate capacity of RACFST specimens were investigated.Three-dimensional finite element method (FEM) model was developed with the commercial finite element software ABAQUS to analyze the RACFST and CFST stubs under axial compressive loading and the results were validated by the experimental results.A parametric analysis was conducted to investigate the influence of the RAC strength, RCA replacement percentage, steel strength and ratio of steel area over concrete area on the static behavior of the axially loaded RACFST stubs using the FEM model. Based on the experimental results and theoretical analysis, the equations were put forward for estimating the stress versus deformation relationship of the steel tube and the RAC core. Then the mumerical ananlysis method was derived for predicting the vertical load versus vertical deformation of the RACFST stubs under axially compressive loading.