PSI - Issue 64

Bartosz Piątek et al. / Procedia Structural Integrity 64 (2024) 1581–1588 Piątek , B., Howiacki, T., Kulpa, M., Siwowski, T./ Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Today, around the world we can observe ongoing development of road and railway infrastructure. The number of bridge structures has been steadily increasing year by year, particularly in developing countries. For instance, over the past two decades, the quantity of these structures on Poland's national roads has tripled. At the same time, the most common material used to build small and middle-span bridges is prestressed concrete. Bridges with such superstructure (post-tensioned or pre-tensioned concrete) currently represent around half of all road bridges in Poland, whereas in 2002, their share was less than 20%. The anticipated growth in the number of prestressed bridges in the coming years is driven by the further expansion of the national road network and the establishment of new railway lines. Similarly, prestressed bridges play a crucial role in the infrastructure systems of other countries. The main reason behind the rapid growth of such structures is their reputation as highly durable constructions, requiring minimal maintenance throughout their operational lifespan when designed and constructed correctly. However, incorrectly designed or constructed prestressed bridges are vulnerable to environmental factors, leading to a shortened operational lifespan and a gradual decrease in load-bearing capacity over time. These structures are subjected to substantial prestressing forces during construction, making them unfortunately highly sensitive to any design or construction errors. In extreme cases, this can result in structural failure or c atastrophe (Anania, Badalà, & D'Agata, (2018); Hurlebaus, Hueste, Karthik & Terzioglu, (2016); Powers, Sagues & Virmani, (2002)). Consequently, quality control during the construction phase and heightened attention to periodic bridge inspections during operation are essential (Bonopera, Chang, Lee, (2020)). Identifying localized damage in prestressed bridges is challenging with current methods due to the location of tendons within the concrete cross-section (Mazzatura, Salvatore, Caprili, Celati, Mori & Gammino, 2023). Early-stage diagnostics of damage allow for the prevention of further deterioration to an acceptable safety level of the structure and prompt implementation of remedial measures, which are often less costly at this stage (Frangopol, Saydam, & Kim, (2012)). A promising and continually evolving technique in the field of diagnostics and monitoring of concrete structures is the use of distributed fiber optic sensors (DFOS) (Alj et al., (2021); Bado, Casas & Kaklauskas, (2021); Bednarski et al., (2022); Buda- Ożóg et al., (2022)). The paper presents the research results on the development of a DFOS system for monitoring and diagnosing post tensioned concrete bridges (Piątek et al. , (2023)), addressing the road administration’s needs in this area. Comparison of measurement methods using various DFOS sensors, measurement results of displacements, strains, and crack width as well as the identification of damages using this measurement technology are presented. Preliminary studies have demonstrated that the DFOS system can detect damages, primarily voids in the grout inside cable ducts, which are the most common causes of strand failures. The use of continuous geometric measurements with DFOS sensors enables a comprehensive understanding of structure behavior along the length, which is unattainable with typical spot sensors. 2. Research Program The research was conducted as part of the project aimed to determine the suitability of various distributed fiber optic sensors for the diagnostics and monitoring of post-tensioned concrete structures. The preliminary research was carried out on the quasi post-tensioned beams on a small scale (with embedded cable ducts and tendons, but without tensioning), which were intended to provide initial insight into the quality of measurements obtained using selected DFOS sensors. Following the preliminary studies, post-tensioned beams with curvilinear multiwire strands on a bigger scale (close to natural) were carried out. Within these both studies, a total of four concrete beams equipped with a DFOS system were tested:

• QPT1 – quasi post-tensioned small-scale beam without damages, • QPT2 – quasi post-tensioned small-scale beam with damages, • PT1 – post-tensioned full-scale beam without damages, • PT2 – post-tensioned full-scale beam with damages.