Detection of Top-Bar Effect in Reinforced Concrete Using Guided Ultrasonic Waves

Abstract

An ultrasonic shear wave-based nondestructive method is proposed in this paper to detect steel–concrete interface debonding owing to the top-bar effect. A concrete wall was cast with horizontal reinforcements at different heights in order to create interfacial defects underneath the top bars. Lead zirconate titanate (PZT) patches were surface mounted at the ends of the bars to excite and record shear waves. The ultrasonic results showed that the amplitude of the signals increased with the height of the bars. The specimens were cut open after the experiments and the top-bar effect was clearly discerned. Its increase with the height of the bar was clearly observed. An increasing difference between the high-frequency component (HFC) and the excitation frequency of the signal was observed between the bottom bar with a good bond and the top bars. This feature can be utilized for nondestructively monitoring the top-bar effect.