PSI - Issue 47

Shakiba Zolfaghari et al. / Procedia Structural Integrity 47 (2023) 398–407 S. Zolfaghari et al./ Structural Integrity Procedia 00 (2019) 000–000

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(2018), and Mostofinejad and Hajrasouliha (2019)) has been investigated. In defining the bond behavior of sheet to concrete, the bond strength is of special importance. In many studies, the bond strength is considered as the maximum load that the joint has endured in the loading process until complete failure. But since the maximum load occurs after the beginning of separation of the sheet from the concrete surface, in order to design safely and reliably, the load corresponding to the starting point of separation should be defined as the bond strength. In ASTM D3039/D3039M-17 (2017), there is also a difference between maximum applied force and bond capacity. In this research, considering the two approaches of maximum load and debonding load, the impact of changes in groove dimensions (various widths and depths) on the bearing capacity of the FRP-concrete joint is studied. In Section 2, specimens and experimental program will be introduced, and Section 3 will be dedicated to presenting the results of the experiments and their analysis, and in Section 4, the results will be summarized. 2. Experimental program To achieve the mentioned goals, the way of defining laboratory specimens is of special importance. In this research, single-lap shear tests were performed along with one repetition of each test on prismatic concrete specimens with dimensions of 350 × 150 × 150 mm (length × width × height), strengthened with CFRP sheet. All displacements and the longitudinal and transverse strain field created in the specimens were measured by the particle image velocimetry (PIV) method. As seen in Table 1, the specimen strengthened via the externally-bonded reinforcement method is named EBR and the specimens strengthened via the externally-bonded reinforcement on grooves method are named EBROG-groove width × groove depth.

Table 1. Specifications of specimens and test results.

Increase in debonding load compared to EBR (%)

Groove cross sectional area (mm 2 )

Increase in maximum load compared to EBR (%)

Bond debonding load (kN)

Specimen Name

Groove width (mm)

Groove depth (mm)

Bond maximum load (kN)

-

1 2 3 4 5 6 7 8 9

EBR

-

-

-

8.30 9.85

-

8.00 9.70

21.2 26.2 12.5 28.4 49.7 24.2 45.9 16.6 31.7 39.4 40.0 53.7

EBROG-2.5×2.5 EBROG-2.5×5 EBROG-2.5×7.5 EBROG-5×5 EBROG-5×10 EBROG-5×15 EBROG-10×5 EBROG-10×10 EBROG-10×15 EBROG-15×5 EBROG-15×10 EBROG-15×15

2.5 2.5 2.5

2.5

6.25 12.5

18.7 29.9 14.7 33.6 52.5 35.9 73.5 29.5 29.4 54.9 45.5 62.7

5

10.78

10.10

7.5

18.75

9.52

9.00

5 5 5

5

25 50 75 50

11.09 12.66 11.28 14.40 10.75 10.74 12.86 12.08 13.50

10.27 11.98

10 15

9.94

10 10 10 15 15 15

5

11.67

10 15

100 150

9.33

10 11 12 13

10.54 11.15 11.20 12.30

5

75

10 15

150 225

By conducting uniaxial compressive strength test on 100 × 200 mm (diameter × height) cylindrical concrete specimens according to ASTM C39/C39M-18, at the time of the single-lap shear tests, the average compressive strength of concrete used in the construction of concrete prisms was 23.1 MPa. The mechanical specifications of carbon fibers and glue used for strengthening are listed in Table 2. An FRP sheet with a thickness of 0.17 mm and a width of 48 mm was used to strengthen the specimens. The length of the connection between the sheet and the concrete surface was 200 mm (considering 35 mm of the length without connection to prevent stress concentration near the place of load application). The EBR and EBROG techniques were used to strengthen the specimens with the implementation steps described in the Introduction Section. Sikadur-31 was used to fill all the grooves (except for the 2.5 mm wide grooves) and