Damage Assessment Methodology Of In-service Brick Masonry Structure Based On Acoustic Emission Technique

At present,masonry structures make up a considerable proportion in the form of building structures worldwide.The damage of the masonry structures is usually manifested in the form of surface cracks and internal voids.Therefore,investigation of the damage state such as cracks is of great importance to realize the health monitoring of in-service masonry structures.Based on acoustic emission(AE)monitoring technology,the propagation attenuation characteristics of AE signals in brick masonry specimen were studied.Two tests were carried out in this dissertation: uniaxial compression test of brick masonry specimens in laboratory and the in-situ compression test of in-service brick masonry wall.Then,the characteristics of AE parameters in the two tests were discussed and analyzed in detail.Finally,the AE rate process theory was introduced into the quantitative evaluation of brick masonry material damage.The main works of this dissertation are listed as follows.The pencil-lead break tests were used to simulate the AE source,and the propagation attenuation characteristics of the AE signal in the brickwork were analyzed.Based on the statistical analysis of AE rising time,the AE time parameters(PDT,HDT,and HLT)were determined.According to the attenuation law of the signal amplitude,the maximum distance limit of the AE sensor was determined.To study the variation characteristics of AE ringing count,energy and peak frequency during the entire loading process,uniaxial compression tests of brickwork specimens were performed in laboratory based on AE monitoring.The results showed that the change of ringing count and energy was consistent with the failure process of the test.According to the curve of ringing count and energy,the whole test process can be divided into three stages.In the failure stage,the proportion of AE signals in low frequency band was significantly higher than that in high frequency band,which can be seen as a precursor to the local failure of the brick masonry members.The characteristics of AE ringing count,energy,peak frequency and b value of in-service brick masonry wall under in-situ uniaxial compression test were studied.The characteristics of AE parameters under the two tests were discussed and analyzed.The results showed that the three stages of damage expansion in brick masonry were identified qualitatively according to the variation of these parameters.Based on the application in the damage assessment of brittle materials such as concrete,the mathematical models of AE rate process theory were introduced into the quantitative evaluation of damage of brick masonry material for the first time.The results indicated that the change law of the probability density function f(V)under the Dai model was more consistent with the formation and development of micro-cracks in the brick masonry,and this model was suitable for real-time assessment of dynamic damage in the brick masonry.Furthermore,a strong linear correlation between the number of AE events and the damage parameter was established,according to which the damage degree increment(?D)of the brick masonry materials can be obtained.