PSI - Issue 64

Sadeq Mo. Annooz et al. / Procedia Structural Integrity 64 (2024) 1565–1572 Annooz, Williams, and Myers / Structural Integrity Procedia 00 (2024) 000–000

1570

6

Table 5 shows the test results and the normalized test results. Eq. 1 was used to calculate the Average bond strength along the embedment length.

Table 5. Test results.

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�������� � �� ����� 63.11

Material

Bar size

Peak load (KN)

Avg. peak load (KN)

Avg. Bond strength (MPa)

Avg. Bond strength (MPa)

45.83 54.29 86.77 80.33 39.33 29.65 31.19 61.49

#4

50.06

24.91

22.18

Steel

#6

83.55

105.76

18.55

94.00

16.49

#4

33.39

42.10

16.61

37.49

14.80

BFRP

#6 66.51 63.36 Table unit conversion: N = 0.22 lb, 1 MPa = 145 psi . 63.79

79.61

13.96

71.26

12.50

The bond strength of #4 BFRP and #6 BFRP is 34% and 25%, respectively, less than that of mild steel. Rebars with larger diameters have lower bond strength. As per (Baena et al. 2009), larger diameter rebars exhibit lower bond strengths with concrete. During testing, the peak bond stress shifts from the loaded end to the unloaded end, resulting in a non-linear stress distribution along the rebar. This phenomenon is more pronounced in larger rebars due to the longer embedment lengths, which contribute to reduced average bond strengths. Furthermore, the Poisson effect causes a more significant reduction in diameter for larger rebars under tension, leading to decreased frictional and mechanical locking stresses. The size effect concept also indicates that larger rebars have lower bond strengths due to their brittle failure mode and increased elastic energy. These factors - non-linear stress distribution, Poisson effect, and size effect - collectively diminish the bond strength of larger-diameter rebars. Mild steel has higher bond strength because, in addition to the friction force, it has bearing force generated by the rebar’s ribs, as shown in Figure 6. Due to the friction between the concrete and the BFRP rebar, BFRP residue was found attached to the concrete surrounding the rebar, and a reduction in the rebar size was found, as shown in Figure 7.

Figure 6. Type of forces applied on mild steel rebar (left) and BFRP rebar (right).