Investigation On Damage Mechanisms Of Civil Structures Based On Acoustic Emission Technique

Security and durability of the civil engineering structure has always been a hot topic of concern,and it is also one of the core of structural design.Monitoring structural damage effectively and providing early warning is the pursuit of engineers.There are a lot of damage identification methods,acoustic emission(AE)is a real-time nondestructive testing method,and has got a rapid development in recent years.This technique is based on the detection of transient elastic waves produced by internal micro placement because of plastic deformation or cracks propagation in material.Because of high sensitivity,good robustness and many other advantages,has been widely used in structural damage detection and material performance evaluation.In this paper,AE technique was applied to investigate the damage mechanism of several typical civil structures,the major research contents of this thesis were summarized in three parts:Firstly,acquired AE signal of carbon nanofibers modified composite under uniaxial tension.The curve of cumulative AE hits can reveal the damage evolution of modified composite.Preliminary tries for damage identification were made through the peak frequency.Finally,fuzzy c-means algorithm was used to cluster the AE signal and could identify each damage model more accurately.Different content of carbon nanofibers brought about different mechanical properties,and mechanical properties of the different lead to different AE characteristics.Secondly,AE technique was applied to monitor failure process of steel tube confined reinforced-concrete column(STCRC)under uniaxial compression.The damage evolution of the short column was investigated based on the cumulative energy and AE rate.According to the distribution between frequency peak and amplitude,the preliminary classification of structure damage was obtained.RA value and average frequency can discriminate the crack of core concrete qualitatively,the classification of data set was achieved by using Gaussian mixture model(GMM)in this paper.The trend of crack propagation under different load was analyzed,and the final results were consistent with the practice.Thirdly,experimental pull-out test was conducted on reinforced concrete specimens with the different corrosion degree,and AE technique was applied to monitor the whole failure process in real-time.Decending of bonding capacity was investigated from the microscopic perspective.AE characteristics of different specimens.AE intensity analysis was performed and intensity quantification chart was established.By using the theory of AE rate process,correlate relationship between the value of rate parameter and the corrosion degree.