Acoustic Emission Generated in Corners of Reinforced Concrete Rigid Frame Under Cyclic Loading

摘要

A fundamental study was made of the acoustic emission (AE) behavior of reinforced concrete structures under cyclic loading. The growth of tensile cracks, shear cracks and bond failure of the reinforcement in an "L" shaped rigid frame of reinforced concrete was monitored by AE. The results were compared with visual observation and the measured value of crack widths and deflections. From the tests, it was shown that different AE sources could be clearly discriminated by comparing the AE parameter data with the results of visual observation and crack width measurement. It was revealed that the Kaiser effect exists so long as the width of tensile cracks is smaller than about 0.15-0.20 mm (0.006-0.0078 in.). However, it fails after the width has reached this value and with the onset of shear cracks. The Kaiser effect, thus, becomes a very effective method for estimating the level of deterioration in concrete structures. Moment tensor analysis, a quantitative AE waveform analysis based on the moment tensor modeling of cracks, was applied to classify crack types and to determine crack orientations in the fracture process of a rigid reinforced concrete frame. Crack orientations determined from eigenvectors obtained by decomposition of moment tensor components and crack directions presented as crack-opening vectors for tensile cracks and fault-motion vectors for shear cracks were in good agreement with the visual observation of the surface cracks. The moment tensor analysis showed that shear cracks start to appear and play a primary role when the Kaiser effect fails.