Study on axial compressive damage performance of SMA strips confined concrete columns by acoustic emission technology

The shape memory effect induced by thermally exciting shape memory alloy (SMA) provides an active constraint method for structural reinforcement. To investigate the axial compression performance and failure mechanism of SMA strips confined concrete columns, axial compression tests and real-time acoustic emission (AE) monitoring were performed on concrete columns with diverse pre-strain levels and constraint methods. The results reveal that the constraint of SMA strips improves the mechanical properties and inhibits the brittle failure. Based on the correlation between AE characteristic parameters and stress–time curves, the internal failure of confined specimens is classified into three stages: micro-crack initiation, crack stable development and macroscopic crack formation. The rise angle value grows and average frequency value reduces as the damage progresses, manifesting that the shear crack is in the stable propagation stage. The b-value generally diminishes as the load rises, illustrating that the cracking level inside the specimen is continuously increasing. Moreover, compared with the PC40-50-40 specimen, the AC40-50-40 specimen generates highly active AE signals. The distribution of AE damage events indicates that active constraint significantly accelerates the initiation and propagation of cracks in concrete columns during compression loading.