A multi-physical approach for crack monitoring in prestressed concrete girders: A case study

This article presents a multi-physical crack monitoring approach for prestressed concrete girders, combining ultrasonic pulse velocity (UPV), acoustic emission (AE), and strain measurement by distributed fiber optic sensors (DFOS) within a cyclic loading scheme. The proposed approach was applied to a prestressed concrete girder extracted from a decommissioned bridge built in 1981. The results demonstrated the strength of this multi-physical approach for monitoring a broad spectrum of crack behaviors in prestressed concrete structures. It can identify existing cracks with minimal loading. The applied load levels were below the estimated decompression force. Additionally, the approach can distinguish between the formation of new cracks and the growth of existing ones. Notably, the formation of new cracks led to a more significant reduction in local stiffness, as indicated by the force and DFOS strain measurements. Furthermore, a potential relationship was observed between the AE hit rate and the DFOS strain rate during the formation of new cracks. Moreover, this approach enabled detection of possible damage inside the structure such as at the interface between the cast-in situ overlay and the precast girders or in the internal web. This study contributes to the development of more comprehensive monitoring strategies for aging prestressed concrete structures.