PSI - Issue 64

Emanuele Gandelli et al. / Procedia Structural Integrity 64 (2024) 685–692 Emanuele Gandelli / Structural Integrity Procedia 00 (2019) 000 – 000

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application of the FDD to two peculiar case-studies: (1) a PCB with bonded strands affected by an "almost pure" shear-crack pattern; (2) a PCB equipped with unbonded strands affected by an almost negligible (i.e., reversible) flexural damage. The main findings were: (a) in the first case, characterized by a relatively extensive shear-crack pattern, the damage was associated to a significant variation in the fundamental frequency of the PCB (about -7%) and a minor alteration of the relevant mode shape; (b) in the second case, it was found that identified natural frequencies were not effective in detecting the damage. Indeed, once the source of damage was removed (i.e., the vertical load), the cracks self-closed restoring the original fully-reacting cross-section. Conversely, a qualitative comparison between undamaged and damaged mode shapes was helpful to localize the damage; (c) at last, despite the conflicting opinions of some authors, it was found that the FDD technique is not a suitable tool to assess the potential influence of the strands’ prestressing level on the fundamental frequency of PCBs. This was demonstrated through hammer tests carried out on a PCB with unbonded strands. Despite the pre-compression load, in beam-2, was step by-step decreased from 1126 kN to 577 kN (i.e., -49%), the fundamental frequency remained practically unvaried (from 17.40 Hz to 17.37 Hz, i.e., -0.17%). References Allemang, R.J., Brown, D.L. (1982). A correlation coefficient for modal vector analysis. Proceedings of the 1st International Modal Analysis Conference, Orlando, Florida. Bonopera, M., Chang, K.C., Chen, C.C., Sung, Y.C., Tullini, N., 2019. 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