Damage evaluation and failure mechanism analysis of axially compressed square concrete-filled steel tubular columns by acoustic emission techniques

•The damage process of axially loaded concrete-filled steel tubular column can be divided into 5 stages.•The strongest signal monitored before peak load indicated the concrete reached failure strain.•Cumulative acoustic emission energy, amplitude, hits were linearly related to load.•Stages Ⅰ-Ⅲ1 reflected the damage properties of plain concrete, and stages Ⅲ2-Ⅴ reflected the confined concrete.•Specimens with small sizes and thin walls were more obviously confined. Concrete-filled steel tubular (CFST) columns are widely used as major load-bearing components in structures due to their excellent load-bearing properties. However, the presence of steel tube makes it difficult to accurately assess the damage level of concrete by traditional mechanical measurements alone. This paper investigated the efficiency of acoustic emission (AE) technique in assessing the damage characteristics of the concrete in CFST columns. The damage properties of four axially compressed square CFST columns with the widths of 500–1000 mm and the width-to-thickness ratios of 40 and 50 were analyzed through AE signals. According to the AE results, the axial compression progress of specimens could be divided into five stages. Then, through the correlation analysis, the cumulative AE energy, amplitude, and hits were found to be linear related to the applied load. Finally, the damage percentage of each specimen at different stages was discovered to be influenced by width and width-to-thickness ratio.