PSI - Issue 64

Szymon Grzesiak et al. / Procedia Structural Integrity 64 (2024) 269–276 S. Grzesiak, C. de Sousa, M. Pahn / Structural Integrity Procedia 00 (2019) 000 – 000

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a dedicated test facility (see Fig. 1a) and repeated three times (test series B1, B2 and B3). The samples pertaining to test series B3 were scanned with CT after the bending test. For the calculation of the bending test some properties of FRP stripes were empirically determined. Table 1 presents the experimental program and additional information regarding the sample geometry. Table 1. Experimental program and sample geometry (*Samples from B3 were scanned with CT after the bending test). Test series Samples Steel reinforcement (mm 2 ) FRP reinforcement (mm 2 ) Concrete cross section (mm 2 ) B1 Beam 1 & 2 Ø8 → A s1 = 50 with ρ s1 =0.015 b f × t f = 32 × 3 → A f = 96 b c × h = 50 × 65 → A c = 3250 B2 Beam 1 & 2 B3* Beam 1 & 2 2.2. Test sample and used materials The test samples contained a steel reinforcement bar (B 500 A) with a diameter of 8 mm. A concrete cover of 20 mm was adopted and no shear reinforcement was provided. The concrete samples were cast using the mix shown in Table 2. A normal concrete with strength class C20/25 was selected. The concreting and hardening process are showed in Fig. 1b and 1c. The total length of the concrete samples, with cross-section 50 mm × 65 mm, was equal to 500 mm. The span between supports was equal to 400 mm. After the casting and hardening process, the concrete surface intended for application of FRP strengthening was sanded and roughened. The BFRP strip was then applied using 2-component epoxy resin adhesive S&P Resin 220 HP. The distance of the FRP strip to the end supports a f was 10 mm on both sides. In association with other published work Grzesiak, Pahn and Schultz-Cornelius (2022 b), a basalt fiber reinforced strip with cross section 32 mm × 3 mm was externally glued. This process led hence to BFRP strip being bonded to what can be considered as the bottom surface of the samples as an external reinforcement in order to be representative of real case situations. The properties of used materials are provided in Table 2.

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Static system:

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Coordinate system:

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2·F

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Beam 1

Beam 2

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Fig. 1. (a) test setup with: ① hydraulic cylinder, ② Support condition (rotation around the x-axis), ③ concrete sample with cross-section 50 mm × 65 mm, ④ location of steel reinforcement in concrete sample, ⑤ location of FRP strip; (b) concreting and (c) hardening process The test setup shown in Figure 1 is a three-point bending test, which directly considers two concrete specimens at the same time. Two hydraulic cylinders applied the load at one end of the beam samples and two load cells measured the corresponding applied force. The test setup is completed by a small steel roller, placed in the centre of the concrete specimens to transfer the force from one specimen to the other. Further details of the adopted test setup are given in Giese and Herbers et al. (2023); Liebold and Wagner et al. (2023).