Axial compressive behavior and damage evolution mechanism of SMA-repaired pre-damaged RC columns using acoustic emission monitoring

With the increasing saturation of existing building stocks, the rehabilitation of damaged reinforced concrete (RC) structures has emerged as a research priority. This paper proposes a repair scheme for damaged RC columns using shape memory alloy (SMA) strips for circumferential confinement. Nine groups of RC column specimens were designed. Axial compression tests were conducted to investigate the axial load–displacement responses of specimens with varying levels of pre-damage and different numbers of SMA strips. Meanwhile, acoustic emission (AE) technology was employed to monitor the damage evolution in real time, and key AE characteristic parameters, including ringing count, signal energy and b -value were analyzed. The axial compression test results indicate that the failure mode of SMA-repaired specimens shifts from brittle to ductile. After repairment, the ultimate load-bearing capacity increases by up to 30.5%, and the ductility coefficient improves by a maximum of 6%. The repair effectiveness increases with a higher number of SMA strips but decreases with more severe pre-damage. For specimens with low to moderate pre-damage, a configuration of four SMA strips is recommended. Analysis of the AE parameters reveals the repair mechanism of the SMA strips: at the initial damage stage, the SMA strips suppress microcrack propagation through active prestressing; during crack propagation and coalescence, the combined active and passive confinement provided by the SMA strips reduces the overall frequency of damage events at the macroscopic level. At the microscopic level, this leads to a reduction in the proportion of shear-induced cracks at failure, with a reduction of 7.3–13.7% depending on the specimen. The findings provide theoretical support for understanding the damage control mechanisms of SMA-repaired damaged structures.