Theory And Application Of Damage Detection In Prestressed Concrete Based On AET

Acoustic emission is a nondestructive testing technique to monitor defect formation and failures in materials according to the stress wave traveling through materials. Comparing with other techniques, it is real-time, dynamic, convenient and used widely. In this thesis, studies and experiments on the application of acoustic emission in the damage detection of prestressed concrete structures are present.A series of prestressed concrete beams are loaded in three points bending until failure. Crack initiation and propagation due to bending are monitored and compared with observation. The waveform acoustic emission signals are also recorded by SWAES. Based on the results of the relationship between the cumulative energy or happening ratio of acoustic emission and time, the failure process of the specimens are divided into four different destruction states and moreover the typical waveform acoustic emission signals of eacht destruction state are picked up, then spectral analysis and wavelet analysis are carried out. The comparison of the amplitude and frequency of waveform acoustic emission signals in time domain and frequency domain in different destruction states shows that the failure process of prestressed concrete beams is the same as concrete beams under three point bending in some aspect. The critical state of prestressed concrete beams are found by Gabor wavelet analysis, there are many marked chatacters during the failure process of the prestressed concrete specimens. Thus, we can draw a conclusion that waveform acoustic emission signals can be used to disclose the characteristics of the different damage levels of prestressed concrete beams under loading in real time.These conclusions result from the experiments carried out in the laboratory, and they might need some deeper reasoning and improvement if it is applied to the engineering practice.