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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1. Introduction Recent pilot projects (Grabe et al., 2020; Lazoglu, et al., 2023) demonstrated the potential of digital infrastructure maintenance and it is expected that its importance rises in the next decades. Strong research interest is put on structural health monitoring (SHM) and digital twins as possible coping strategies to extend the lifespan of ageing infrastructure (Bado et al., 2022). The overarching goal is to augment the established maintenance process by novel data driven methods and the transformation towards predictive maintenance based on digital twins (Herbers et al., 2024). Digital twin based SHM techniques require a holistic monitoring system and methods for automated data processing and information aggregation (Sawo et al., 2023). Distributed fiber optic sensors (DFOS) can be used to monitor parameters such as temperature, vibration, settlement, inclination or strain with high spatial resolution down to a sub-millimeter range (Chamoin et al., 2022). Enabled by the quasi-continuous measurement capability, DFOS can be deployed without requiring knowledge of the precise location of later interest and type of yet to develop damages, which is a huge advantage over conventional spot sensors. DFOS make it is possible to investigate a wide range of effects, from e.g., cracking of large-scale pretensioned girders during the manufacturing process (Herbers et al., 2024), down to small-scale bond interactions in reinforced concrete specimens (Galkovski et al., 2021; Koschemann et al., 2022). Hence, both the structure’s global behavior (e.g., deformation) and local effects (e.g., cracks) can be measured simultaneously (Chamoin et al., 2022; Herbers et al., 2024) with DFOS. Thus, DFOS offer potential for SHM, especially from the beginning of a structures’ existence. This contribution presents two research projects, IDA-KI and smart_tendon, employing DFOS to achieve the overarching goal of a data driven condition assessment. Together, a load test on a prestressed concrete girder was conducted, investigating the capability of various DFOS application methods to detect structural anomalies (e.g., damages). 1.1. Research project smart_tendon SHM faces many challenges for describing the actual condition of prestressed concrete structures. In particular, certain issues require special attention, such as longitudinal variation of frictional losses and influence of anchor slip based on theoretical calculations, lack of information on local stress variation in tendons due to live loads and local stress peaks due to cracking of concrete. In addition, some aspects may not be fully assessed by conventional diagnostic methods, e.g., cracks in the bridge deck below the roadbed, local voids in the bonded tendon grout and the localization of defects in the tendon. Development and implementation of suitable DFOS has been the subject of considerable research. Installation is particularly challenging. DFOS for integration into prestressed concrete require individual on-site integration into existing tendon systems as well as robust protection. In addition, a reliable connection to the acquisition unit must be provided during installation. In the future, however, the monitoring system could be integrated directly into the structural elements and monitored from the beginning of their existence, including the assembly and prestressing process. The smart_tendon research project is developing an approach to integrate DFOS in grouted tendons or in prestressing strands. Therefore, a method has been devised that allows a safe DFOS integration prior to installing the tendons; suitable outlets in the grouting caps allowing for sealing during grouting without damaging the fibers. In addition, an access interface solution for the monitoring equipment to the DFOS is currently being evaluated. Integration of DFOS into SHM applications of prestressed concrete structures is expected to provide advantages, including: (1) early age monitoring as basis for digital twins and birth certificates, (2) monitoring systems integrated as standard in new structures at low additional cost, (3) an additional source of information during mandatory bridge inspections and (4) identification and localization of visually undetectable damages (e.g., cracks in the deck slabs). 1.2. Research project IDA-KI and the research bridge openLAB Digital twins require smart and automated routines for data curation, evaluation, and aggregation (Sawo et al., 2015; Smarsly & Law, 2014). The research goals of IDA-KI are threefold. First goal is the development of a concept to monitor structures from the beginning of their existence. Because of the promising potential, DFOS are investigated for several monitoring tasks (Herbers et al., 2023).