PSI - Issue 64

Rui-Xin Jia et al. / Procedia Structural Integrity 64 (2024) 799–806 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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100kHZ was used as the excitation signal and the excitation power range was made to be enhanced from 6V, 8V and 10V in that order. Fig.6 to 7 show the time domain and spectral plots of the rebar guided waves under different excitation powers, respectively. From the time-domain plot, it can be seen that only the amplitude of the waveform changes under different excitation powers. The FFT of the received signal gives a consistent spectrogram under different excitation powers, with only the components of its frequency and the amplitude of the fundamental frequency changing. Therefore, the excitation power has no effect on the first wave speed measurement of rebar, and only affects the amplitude of waveform and frequency. The influence of excitation power can not be considered in the actual project.

Fig. 6 Waveforms of different excitation powers

Fig. 7 Spectrogram of different excitation powers

5. Influence of mortar layer Rebar usually has a mortar outer cladding in the bridge web, so it is crucial to consider the effect of mortar when investigating the propagation characteristics of guided waves in rebar. Four thicknesses of specimens of 60mm, 75mm, 110mm and 160mm were set up for the outsourcing thickness, and the length of the mortar specimens used in the test were all 800mm. The mortar was poured using the ratio of cement: water: river sand = 1:0.5:1.5, and then the mortar was filled into the PVC pipe for maintenance. The specimens are cured in a standard curing room, and the test is carried out after the curing has reached a certain strength. The equipment model, connection method and sensor arrangement strategy were kept consistent with the above test. The specimens are shown in Fig.8.

Fig. 8 Specimens with different thicknesses

5.1. Time-domain analysis 100kHz was used to excite the mortar rebar with different outer thicknesses. The time domain plot of the test results is shown in Fig.9. It can be seen that the amplitude of the guided wave is 3.218 V when the thickness of the outer package is 60 mm; 1.909 V when the thickness is 75h; 1.309 V when the thickness is 110 mm; and 0.516 V when the thickness is 160 mm. It is shown that the thicker the thickness of the outer shell, the more the energy of the ultrasonic guided wave leaks into the mortar, which in turn leads to a decrease in its amplitude.