Damage analysis of axially compressed concrete-filled steel tube stub columns based on acoustic emission

Concrete-filled steel tube (CFST) widely applied in engineering structures due to its superior behavior requires monitoring and assessment for damage level. Here, the acoustic emission (AE) technique was used to monitor the fracture process of concrete core in CFST stub columns subjected to axial compression. Test and analyzed results show that the damage process of CFST specimens can be divided into four stages: compaction, elastic-plastic stage, strengthening and secondary strengthening. In the elastic-plastic stage, the evolutionary features of the AE event rate, cumulative energy, Ib-value and crack classification are capable of providing an early warning for cracked concrete core. Full crack propagation can be identified by the rapid increase in the proportion of shear cracks near the inflection point of load, which is impermissible in engineering structures. According to the analyses of the AE event rate and signal intensity in the elastic-plastic stage, the confinement of steel tube with thicker wall thickness or higher strength is delayed, which implies that this confinement is suggested to be triggered early. It is indicated that the AE technique has the potential to monitor and evaluate the damage process of CFST stub columns under axial compression, which can provide additional insight into the failure mechanism and assist in the scheme of repairs.