Interfacial debonding detection for steel-concrete composite structures Part II: Scanning Doppler laser-based MASW and microphone combination-based impact-acoustic vibration

In Part I of this study, the benchmark test and signal calibration of contact and non-contact measurement to quantitatively assess the variation and difference between contact and non-contact measurements. Based on the research findings of Part I, non-contact multi-channel analysis of surface waves (MASW) technique and novel impact acoustic vibration method are proposed in Part II of this study. Aided by scanning Doppler laser vibrometer and a combination of conventional and high-frequency microphones, the feasibility of non-contact nondestructive test (NDT) for SCCS is validated using experimental measurements on steel plate-bonded reinforced concrete (RC) cube with preset interfacial debondings in various dimensions. Since the steel plate at the debonding regions loses the constraint of concrete core, its vibration mode changes obviously. Experimental observations indicate that the accurate location of interfacial debonding can be accurately recognized by noncontact stress wave measurement. Besides, the amplitude of impact-acoustic vibration signal increases remarkably while interfacial debonding occurs, and its frequency spectrum is obviously different from that of healthy regions. Contact NDT techniques, including the impact-response test and impact-transmission test, are also performed for further comparison. Research findings show that the non-contact vibration measurement exhibits high efficiency. More importantly, it can eliminate the test error induced by the additional mass and sensor sticking process. Difference in signal characteristics and imaging precision of contact and non-contact measurement is discussed in detail. In contrast, damage nephogram resolution based on signal amplitude is higher than that of the dominant frequency. Combined with Part I of this study, which focuses on benchmark test and signal calibration, the research findings in this study can lay a solid foundation for improving the detection accuracy of interfacial debondings in SCCS using non-contact NDT techniques.