The world-wide ageing and deteriorating civil infrastructure network has necessitated the development of new Structural Health Monitoring (SHM) approaches that are capable of producing quantitative feedback on fracture mechanisms in critical civil structures such as bridges in real-time. In this paper, we present a methodology that combines techniques applied in quantitative seismological analyses with the enabling capabilities of the Acoustic Emission (AE) technique in order to gain insight into ongoing fracture processes in concrete structures. The proposed methodology employs the technique of Moment Tensor Inversion (MTI), a key analysis tool in seismology, in order to develop a full understanding of the physics of the source of fracture and infer its properties. The MTI technique is simple in concept but solution accuracy is highly dependent on the sampling of the wavefield in 3-D, especially in the case where the sensors are all uniaxial. For accuracy purposes, all our experiments were performed using high-fidelity Glaser/NIST point-contact sensors that show a flat response for frequencies between 20 kHz and 1 MHz. In this paper, we provide a general description of the proposed methodology with emphasis on the so-called hybrid MTI technique. Finally, we present a set of initial experiments conducted in the laboratory using repeatable artificial AE sources and we discuss the results.

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