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The use of dynamic response to identify damage in engineering structures has been the focus of several research works in the recent years. Most of the vibration-based damage assessment methods developed thus far require modal properties that are obtained via the traditional Fourier transform (FT). Unfortunately, the Fourier-based modal properties, such as natural frequencies, mode shapes, etc., have been reported to be mainly insensitive to structural damage, and hence are not regarded as suitable damage indicators. This paper discusses the application of piezoelectric sensors used for the evaluation of integrity of adhesively bonded joints in PVC plastic pipes. A systematic experimental and analytical investigation was carried out to demonstrate the integrity of adhesively bonded joints. Besides the commonly used methods, a newly emerging time-frequency method, namely the empirical mode decomposition (EMD), is also employed. Two novel "damage indices" are developed based on the evaluation of vibration signals with the use of EMD and the fast Fourier integration induced energies. The results are compared to the available damage index method based on the wavelet packet transformation (WPT), which has been used in the literature review. As it will be seen, by use of the damage indices, one could effectively detect the integrity of the adhesively bonded joints. Moreover, the energy indices can distinguish the differences among disbond densities in the joints.