Acoustic Emission Mechanisms And Characteristics Of Damage Detection In Reinforced Concrete Components

On account of the complexity of acoustic emission (AE) of damage detection in reinforced concrete (RC) components, a damage decomposition analysis method was used based on elastic wave theory to investigate the damage mechanism of RC components in destruction process. The acoustic emission characteristics were analyzed by using a hybrid analysis method which combined both parameter and waveform analysis. The Hilbert-Huang transform was applied to AE waves to get their three dimensional energy spectrums. Two characteristic parameters of AE signals were extracted, namely maximum instantaneous amplitude of intrinsic mode function and the corresponding characteristic instantaneous frequency. Then a corresponding AE test criteria for detection and evaluation of RC components was set up. The main researches of the dissertation are as follows:Based on elastic wave theory, a finite element numerical model for simulating the common cracking process of concrete components was set up. The AE sources were simulated by moment tenser. The source stimulation, propagation property of ultrasonic wave, and signal reception were studied to reveal the mechanism of AE sources. An installation principle of sensors in AE testing was set up according to the propagation property of ultrasonic wave.A research policy for studying destructions from simple to complex was constructed. Several elemental damage modes (including cracking of concrete, tension of steel bars, bond slipping of steel bar in concrete) were investigated experimentally to study the source mechanism and AE characteristics. A hybrid analysis method which possessed advantages of both fast/real-time of parameter analysis, and comprehensive/accurate of waveform analysis was presented to realize quantitative characterization to AE signals. The Hilbert-Huang transform which features adaptivity in signal processing was employed in waveform analysis. The three dimensional time-frequency energy spectrums of AE signals were derived. Then the maximum instantaneous amplitude of intrinsic mode function and the corresponding characteristic instantaneous frequency which can sufficiently represent source strength and feature were confirmed as two characteristic parameters. According these, a mechanism for distinguishing different AE sources was built.The AE signals of RC components were studied based on the AE characteristics of elemental damage modes. The relationship between general demolition of RC components and elemental tests were established. An AE damage identification criterion for RC components was presented. Based on this, a general RC beam under simple bending state was tested to identify damages. A total time-frequency energy distribution in damage process which can reflect damage states intuitively was derived, thereby realizing quantitative evaluations of damage states to RC beams. The AE test results were verified by using a digital image correlation (DIC) method.The research of this dissertation shows that the parameter-waveform-hybrid analysis method can be used in damage detection of RC structures. The HHT time-frequency energy spectrum quantitative analysis method can be used for quantitative damage evaluation in RC structures, and further be expanded to various damages in civil engineering to finally realize online monitoring in actual structures, and sequentially realize the early warning, quantitative evaluation, and life prediction of structures.