Modal identification of prestressed concrete beams with artificial damage on prestressing strands

This contribution illustrates the preliminary research findings of an ongoing structural health monitoring (SHM) campaign on prestressed concrete (PC) beams with artificially damaged prestressing strands. The specimens have been designed to be representative of a scaled bridge girder belonging to a 4-girder grillage scheme, with the transverse diaphragms here simulated by means of a transversal steel profile crossing and supporting the main girder at its mid-span. The vibration tests are aimed at analyzing serviceability load conditions of these PC girders under different damage scenarios by means of modal identification techniques based on operational modal analysis (OMA). Indeed, the specimens have been manufactured with small holes in their bottom face, thus enabling the execution of some cuts of prestressing strands to artificially simulate damage in the prestressing system at different locations. A network of piezoelectric and MEMS accelerometric sensors are deployed along the beam to capture the main vibration frequencies and mode shapes in the various phases of the experimental campaign. The tests include progressive load levels and different damage scenarios (in terms of locations and amount of strand cuts). The present work may be useful to understand the variation in the modal properties of real-scale PC beams ascribed to prestressing strand damage.