A research program was undertaken to evaluate the influences of steel reinforcing bars oil signals obtained from depth measurements of sui face-opening cracks in reinforced concrete structures based on transient stress waves generated by elastic impact. Numerical studies were performed to gain an understanding of the interaction of transient stress waves with steel bars in concrete structures containing surface-opening cracks. A reinforced concrete beam was constructed as an experimental specimen. The specimen was simply supported and loaded at the center point until cracks occurred. Experimental studies were carried out on the cracked beam. Two displacement receivers were placed on the opposite sides of a surface-opening crack to monitor disturbances caused by the arrivals of stress waves generated by impact. The first receiver and impact were located on the same side of the crack. The first receiver was used to trace the start rime of impact. The second one placed oil the opposite sine of the crack was used to find the arrival time of P-wave propagating through steel bars, and the arrival time of the diffracted P-wave from the bottom edge of the crack, Numerical and experimental results show: that rite presence of steel bars results in an initial disturbance in the waveform recorded by the second receiver because P-waves call propagate across the crack along the steel bars. it is also shown that the shortest travel path Soi a P-wave from the impact point through the steel bars to the second receiver is obtained if rile P-wave is incident upon the concrete/steel interface with a critical angle of incidence. Equations for determining rite depth of steel bars are presented. Because the amplitude of the initial disturbance caused by the steel bars is small, it is still easy to identify the following arrival of the P-wave diffracted from the bottom edge of the crack. Thus, the presence of steel reinforcing bars does not have a significant influence on measuring the crack depth
