Retracted: Characterization of Flexural and Shear Cracks in Reinforced Concrete Beams Using Moment Tensor Inversion from Acoustic Emission Signals

Quantitative characterization of fracture mechanisms in concrete is a challenging problem that has not been convincingly solved to date. Several monitoring approaches have been proposed to capture and characterize different fracture mechanisms and warn against potential sudden structural failure. However, due to the complex nature of concrete, often only qualitative approaches are applied, which are unable to accurately characterize fracture sources in concrete due to intricate and simultaneously occurring fracture processes and significant measurement noise. In this study, the authors further investigate the feasibility of employing a monitoring approach that combines the seismology-based method of moment tensor inversion (MTI) with the acoustic emission (AE) technique for the quantitative characterization of flexural and shear cracks in reinforced concrete beams. To evaluate this approach in a realistic large-scale setting, the authors conducted two laboratory experiments on two separate normal-weight reinforced concrete beams of the same overall dimensions: $305\mathrm{m}\mathrm{m}\times 610\mathrm{m}\mathrm{m}\times 4.88\mathrm{m}$ ($12\mathrm{in.}\times 24\mathrm{in.}\times 16\mathrm{ft}$). Such large-scale experiments are scarce and only very few studies have been conducted to date. One beam was designed to fail in flexure and the second one in shear. According to the proposed approach, AE signals recorded from concrete cracking were inverted using a MTI code that the authors modified to visualize stereographic projections appropriate for structural testing, in order to study the sources of fracture and infer their nature. Furthermore, the authors employed a new high-fidelity point-contact sensor that measures actual displacements, which is the input required for a MTI. The results show that the cracks produced during loading of the flexure beam are dominantly tensile (81%) while the cracks from the shear beam were dominated by shearing (73%). These findings demonstrate the potential of the MTI method for quantitative structural-health monitoring (SHM) of large-scale reinforced concrete beams.