PSI - Issue 78

72 Dario De Domenico et al. / Procedia Structural Integrity 78 (2026) 65–72 The comparison in terms of mode shapes (only for the flexural modes 1, 4 and 5) and corresponding curvature indicator is plotted in Fig. 5. The arrows indicate the position of the inspection holes (and of the strands cut). Each mode shape is normalized independently before computing the modal curvature. It can be noted that, while the first mode is not significantly affected by the damage condition at SLS, higher modes (especially the third-order flexural mode, which is labeled as mode 5 in Fig. 5) exhibit a marked deviation between the undamaged and the damaged cases, despite the relatively compatible natural frequencies already shown in Table 1. Indeed, the peaks of the curvature are exactly localized in the nearby of the inspection hole, across the strands cut. This trend of results was confirmed also for the other beam specimens, namely those with inspection holes at one-third of the clear span and with inspection holes at mid-span, as well as for PC beams with other damage scenarios analyzed in this experimental campaign but not discussed here for brevity. This seems to suggest that the modal curvature can be a reliable performance indicator for damage identification in PC beams under service load conditions, although further investigation is necessary to confirm and generalize this result. Moreover, the use of modal curvature for damage quantification (other than detection and localization) is an ongoing research aim. 4. Conclusions This study introduced an ongoing experimental campaign at the University of Messina focused on vibration tests of prestressed concrete (PC) bridge girders under service and ultimate load conditions. Twelve PC beams were fabricated to assess the impact of artificial damage to prestressing strands on dynamic behavior. A range of damage and loading scenarios were tested, including the effect of a transverse diaphragm. A dense sensor network captured static and dynamic responses, and customized Python-based OMA techniques were applied. Preliminary results show that natural frequencies remain largely unaffected by strand damage, while mode shapes — particularly modal curvatures — are sensitive and promising for damage detection and localization. These findings highlight the potential of vibration-based indicators for non-destructive assessment of internal deterioration. Future work will refine damage indicators and explore complementary techniques, such as fiber optic sensors, to enhance detection capabilities. Acknowledgements The study presented was carried out as part of an activity program financed by the Presidency of the Council of Ministers Department of Civil Protection; this publication, however, does not necessarily reflect the position and assessments of the Department. References Computers and Structures Inc. CSi analysis reference manual for SAP2000® version v26. Berkeley: CA, USA; 2024. Cosenza, E., Losanno, D. 2021. Assessment of existing reinforced-concrete bridges under road-traffic loads according to the new Italian guidelines. Structural Concrete 22(5), 2868 – 2881. Gandelli, E., Rossini, G., Mantelli, S.G., Minelli, F. 2024. Damage detection of pre-stressed concrete beams affected by shear and flexure cracks through vibration monitoring. Eng Struct 304: 117572. De Domenico, D., Messina, D., Recupero, A. 2022. Quality control and safety assessment of prestressed concrete bridge decks through combined field tests and numerical simulation. Structures 39:1135 – 57. Dessi, D., Camerlengo, G. 2015. Damage identification techniques via modal curvature analysis: Overview and comparison. Mechanical Systems and Signal Processing 52: 181-205. European Committee for Standardization. 2005. Eurocode 2: Design of Concrete Structures - Part. 1-1: General Rules and Rules for Buildings (EN 1992-1-1:2004). Brussels, Belgium. European Committee for Standardization. 2002. Eurocode 0: Basis of structural design - EN 1990:2002 +A1:2005. Brussels: Belgium. Quaranta, G., Carboni, B., Lacarbonara, W. 2016. Damage detection by modal curvatures: numerical issues. Journal of Vibration and Control 22(7): 1913-1927. Wahab, M. A., De Roeck, G. 1999. Damage detection in bridges using modal curvatures: application to a real damage scenario. Journal of Sound and vibration 226(2): 217-235.