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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2.3. Test setup The QPT beams were loaded in a three-point bending scheme, while the PT beams were loaded in a four-point bending scheme, on specially designed test stands equipped with hydraulic actuators with a maximum force of 630 kN. The theoretical span of the QPT and PT beams was 1.2 m and 7.2 m, respectively. Views of both beams on the test stands in the laboratory are shown in Fig. 3.

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b)

Fig. 3. View of QPT (a) and PT (b) beams on the test stands.

2.4. Instrumentation All beams were equipped with a series of DFOS: bare optical fibers (G) ( Howiacki, Sieńko & Bednarski, (2024) ), composite monolithic sensors with high axial stiffness EpsilonRebar (ER) with Young's modulus E=50 GPa (embedded in GFRP reinforcing bars), monolithic sensors with reduced stiffness EpsilonSensor (ES – inside cross section, EG – on external surfaces, ED – inside ducts), with E=3 GPa (Bednarski et al., (2022)), displacement sensors equipped with 4 optical fibers placed around a rigid core (3D) (Bednarski et al., (2021)), and fiber optic sensors integrated with the prestressing strand (F) developed within this research project (Piątek et al. 2023) . Layouts of the DFOS in subsequent beam cross-sections are presented in Fig. 4. Additionally, reference spot measurements were conducted for comparison with the DFOS results. Electro-resistance strain gauges were used for strain measurements, while linear variable differential transformer (LVDT) transducers were employed for displacement measurements. Force measurements were carried out using load cells integrated with the loading system. The measurements were performed statically, using Luna OBR4600 optical reflectometer, with an accuracy of ±1 µe. The results were read at measurement points spaced 10 mm apart along each sensor. All measurements were performed in the laboratory under constant temperature, therefore no correction was taken into account in the post-processing of the measurement data.

Fig. 4. Locations of DFOS sensors in the cross-sections of tested beams.

3. Small-scale test results (QPT beams) 3.1. Comparison of the sensors ’ measuremen ts

One of the aims of QPT beams testing was to check if the DFOS system can be effectively used inside concrete elements and is resistant to pouring and hardening processes as well as which type of DFOS sensor is the most