Start Date

10-5-2017 11:00 AM

End Date

10-5-2017 1:00 PM

Subjects

Structural frames -- Design and construction, Iron and steel buildings -- Thermal properties -- Mathematical models, Finite element method, Iron and steel building -- Joints -- Testing

Description

Ultrasonic testing is a non-destructive approach commonly used to evaluate concrete structures. A challenge with concrete is that it is heterogeneous, which causes multiple wave scattering resulting in longer and more complex wave paths. The recorded ultrasonic waveform can be divided into two portions: the coherent (or early) and the diffuse (or Coda) portion. While conventional methods only use the coherent portion, e.g. the first wave arrival to determine the wave velocity, we are interested in the entire waveform, i.e. until the wave amplitude is completely dampened out. The objective of this study was to determine what portion of the signal is most sensitive to applied stress and the associated formation and propagation of cracks. For this purpose, the squared Pearson correlation coefficient, R2 was used, which provides a measure for the strength of the linear relationship (or similarity) between a reference waveform under no stress and a waveform recorded at a certain level of applied stress. Additionally, a signal energy-based filter was developed and used to detect signals that captured acoustic emissions generated during the loading process. The experimental work for this study consisted of an active monitoring approach by employing a pitch-catch setup with two ultrasonic transducers, one transmitter and one receiver, that were attached to Ø 152 x 305 mm concrete cylinder specimens, which were loaded monotonically to failure. Our results show that applied stress correlates well with the R2 with remarkable sensitivity to small applied stresses. Also, the relationship between R2 and applied stress is linear for an applied stress that is less than 50% of the ultimate stress.

Authors: Ali Hafiz, Thomas Schumacher

Presenter: Ali Hafiz

Persistent Identifier

http://archives.pdx.edu/ds/psu/20084

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May 10th, 11:00 AM May 10th, 1:00 PM

Monitoring of Applied Stress in Concrete Using Ultrasonic Full-Waveform Comparison Techniques

Ultrasonic testing is a non-destructive approach commonly used to evaluate concrete structures. A challenge with concrete is that it is heterogeneous, which causes multiple wave scattering resulting in longer and more complex wave paths. The recorded ultrasonic waveform can be divided into two portions: the coherent (or early) and the diffuse (or Coda) portion. While conventional methods only use the coherent portion, e.g. the first wave arrival to determine the wave velocity, we are interested in the entire waveform, i.e. until the wave amplitude is completely dampened out. The objective of this study was to determine what portion of the signal is most sensitive to applied stress and the associated formation and propagation of cracks. For this purpose, the squared Pearson correlation coefficient, R2 was used, which provides a measure for the strength of the linear relationship (or similarity) between a reference waveform under no stress and a waveform recorded at a certain level of applied stress. Additionally, a signal energy-based filter was developed and used to detect signals that captured acoustic emissions generated during the loading process. The experimental work for this study consisted of an active monitoring approach by employing a pitch-catch setup with two ultrasonic transducers, one transmitter and one receiver, that were attached to Ø 152 x 305 mm concrete cylinder specimens, which were loaded monotonically to failure. Our results show that applied stress correlates well with the R2 with remarkable sensitivity to small applied stresses. Also, the relationship between R2 and applied stress is linear for an applied stress that is less than 50% of the ultimate stress.

Authors: Ali Hafiz, Thomas Schumacher

Presenter: Ali Hafiz