Code assessment and modeling of the axial capacity of recycled aggregate concrete filled steel tube stub columns

In this thesis, a wide range of experimental data and associated analytical results were utilized comparatively to assess the applicability of four widely used design codes (i.e., American Concrete Institute (ACI), Eurocode 4 (EC4), Architectural Institute of Japan (AIJ), and Chinese Design Code for Steel-Concrete Composite Structures (DL/T)) for calculating the capacity of recycled aggregate concrete filled steel tube (RACFST) columns. To this aim, a total of 97 experimental test results on the circular RACFST columns under axial compression were employed to propose a new model for predicting the axial capacity of such composite columns. The test specimens had a length to diameter ratio ranging from 2.0 to 3.5, indicating that they were the stub column and not failing in overall buckling. The proposed model was generated based the technique of gene-expression programming. The independent variables used for the development of the model were outer diameter and thickness of steel tube, length of the column, replacement ratio of recycled coarse aggregate, concrete compressive strength, and yield strength of the steel. A statistical analysis was also conducted to appraise the contributions of each parameter influencing the axial capacity. The analysis of the results exhibited that the proposed model gave reasonable predictions of the axial capacity of RACFST stub columns compared to the current design codes.