Monitoring prestressing wire breaks with distributed fiber optic sensing

This study investigates the detection of prestressing wire breaks (PWBs) in post‐tensioned concrete girders using distributed fiber optic sensors (DFOS). Decommissioned bridge girders were used as test specimen, and a 30 m long DFOS was installed on the girder's tensile surface. The tendon was damaged at one location in seven steps, and the strain changes were measured with an optical distributed sensor interrogator (ODiSI) capable of high‐resolution distributed strain sensing (DSS). The results show that PWBs can be detected and located in uncracked concrete members by measuring strain changes. However, strain changes were small, about single digit μm/m per cut wire, which is in the magnitude of the ODiSI's measurement accuracy and resolution. Thus, the transfer to application for real‐world structural health monitoring use cases is still a challenge. The shape and intensity of the PWB‐caused strain signal depend largely on position of the PWB and DFOS in the cross‐section and the distance between them. This contribution proposes a model for the PWB‐caused strain distribution in the concrete and discusses the requirements for a DSS‐based monitoring concept. One important requirement is distributed temperature sensing for temperature compensation.