Title: Use of Stress Waves for Determining the Depth of Surface-Opening Cracks in Concrete Structures

Author(s): Yiching Lin and Wen-Chi Su

Publication: Materials Journal

Volume: 93

Issue: 5

Appears on pages(s): 494-505

Keywords: concrete; nondestructive testing; surface-opening cracks; time domain.

DOI: 10.14359/9855

Date: 9/1/1996

Abstract:
The objective of the studies presented in this paper was to determine the depth of surface-opening (visible) cracks in concrete structures with the use of stress waves so that a safety evaluation of such cracked structures can be subsequently performed. Laboratory specimens containing vertical and inclined surface-opening cracks with known depths were used in the studies. Two displacement transducers were placed on the opposite sides of a sur$ace-opening crack to monitor disturbances caused by the arrivals of stress waves generated by elastic impact. The recorded displacement waveforms were analyzed primarily in the time domain. Frequency analysis was also performed to complement the signal analysis. It is shown that as impact is applied on one side of a surface-opening crack, the P-wave arrival diffracted from the bottom edge of the crack causes an initial disturbance and is easy to identify in the waveform recorded at a transducer located on the opposite side of the crack. In addition, the time of impact initiation can be obtained by identifying the R-wave arrival in the waveform recorded at a transducer on the impact side. As a result, the P-wave travel time from the impact point through the crack tip to the receiver on the opposite side of the crack can be obtained to determine the crack depth. In addition to the time-domain analysis, frequency analysis can be used to ascertain whether the surface-opening crack under testing is approximately perpendicular to the surface.