PSI - Issue 64

Bertram Richter et al. / Procedia Structural Integrity 64 (2024) 1208–1215 Richter et al. / Structural Integrity Procedia 00 (2019) 000–000

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flattened out over time and the cracks closed again due to creep recovery. In these and also other tests on prestressed concrete girders, it was observed that existing cracks can be detected based on strain peaks well before decompression is reached. With regard to periodic DFOS measurements, this means that cracks can be detected even at a low load level without the need for expensive load tests. The appearance of new cracks can, for example, indicate particularly high loads between two measurements or other damage mechanisms such as active stress corrosion cracking. The reliability of crack detection under very small loads (below the decompression state) is subject of ongoing research. The FIMT inside the smart_strand shows residual strains as well. The strain peaks at the girder’s ends are probably caused by transverse compression in the anchorage. The helical winding of the FIMT inside the strand causes two effects, both still subject of investigations: (1) oscillations in the strain profile probably caused by changes in lateral compression due to shifts of wires in the strand when realigning under high loads and (2), slightly lower strain values due the fiber’s lay angle to the strand’s axis (Zhu & Chen, 2022). 4. Conclusion Embedding DFOS in concrete structures during the construction process enables monitoring the structure’s condition from the beginning of its existence and detection of structural anomalies at the earliest possible time. To investigate and compare the suitability of different DFOS installation methods and measurement principles for a monitoring from the beginning of a structure’s existence, load tests were performed on a 15m long prestressed precast girder. The DFOS type, installation method and measurement system have a strong influence on the strain profile and the ability to detect cracks and further anomalies. A robust monolithic DFOS embedded directly in the concrete matrix has proven to be a reliable choice for crack monitoring and anomaly detection. Strain profiles provided by a monolithic DFOS glued to the reinforcement were influenced by the surrounding concrete. Both the smart_tendon and the smart_strand were able to capture the strain profile along the girder, allowing monitoring of the prestressing forces. Cracked regions were indicated by a disproportional strain increase. However, due to reduced spatial resolution of Brillouin backscattering and the integration into the strands, single crack identification is not possible. The integration of the DFOS directly into the tendons enables installation without disturbing the construction process, monitoring the prestressing process and verification of calculative assumptions regarding the actual prestressing forces. Early age monitoring information could be integrated into issued “birth certificates” for concrete structures. This contribution presented the joint research and synergetic effects between the projects IDA-KI and smart_tendon. We want to conclude with an encouraging call for joint ventures across research projects. Collaboration proposals regarding further investigations on the openLAB are welcome. Acknowledgements This article presents some results of two research projects funded by the German Federal Ministry for Digital and Transport, within the innovation program mFUND: smart_tendon (“Acquisition of structural data by means of spatially resolved strain sensors integrated in tendons”, funding reference: 19FS2023A-F) and IDA-KI (“Automated assessment of monitoring data for infrastructure constructions using AI and IoT”, funding reference: 19FS2013A-D). We would like to thank the funding authority for their financial support and all of our research partners for the productive cooperation within the projects.

ORCiDs Bertram Richter 0000-0002-3833-8424

Dennis Messerer Kerstin Speck Christian Gläser Steffen Marx

0000-0002-0981-1542 0000-0003-1871-9120 0009-0005-2006-7952 0000-0001-8735-1345

Max Herbers Jakob Laukner Frank Jesse

0000-0002-2187-1652 0009-0003-8958-9279 0000-0002-8165-0261