Axial Compressive Experiment on Steel-Jacket Retrofitted Column with Recycled Aggregate Concrete

To realise the goals of energy saving and emissions reduction in the construction industry, a new retrofitting method of steel-jacket retrofitted columns with recycled aggregate concrete is presented. An unstrengthened column, twelve steel-jacket retrofitted columns, and two concrete-filled steel-tube columns were tested under concentric compressive loading. The axial resistance and deformation capacity were analysed, and the method for calculating the strength of the retrofitted column was evaluated. The experimental results indicated that the strength of the retrofitted columns is 2.19–3.98 times higher than that of the unstrengthened one. In addition, the stiffness and ductility of the steel-jacketed columns increased notably. The strengths of the retrofitted columns with recycled aggregate concrete were 91.8%–97.0% of that of the column with normal infill concrete. As the strength of the infill recycled concrete increased from 27.0 MPa to 32.9 MPa, the strength of the retrofitted column increased by only 2.67%. For specimens with the replacement ratio of recycled coarse aggregate of 50%, the strength of the retrofitted column was enhanced by 34.0% and 77.8% as the thickness of the steel jacket increased from 1.81 mm to 3.84 mm and to 5.84 mm, respectively. After considering the preload of the original column, the strains corresponding to the peak load of the retrofitted column decreased by 47.1%–59.3%. The performance of the steel-jacket retrofitted column was similar to that of the concrete-filled steel-tube columns. Various methods from current design codes were adopted to calculate the axial resistance of the steel-jacket retrofitted column and it was seen that the design code EC4 provides the most accurate and stable predictions.