Discussion and Analysis

Shear Interface Bond Slippage Behaviour

In order to investigate in detail the bond behaviour at the shear interface for the double shear test specimens, the bond slippage behaviour along the interface was characterized using two different methods. The first method used the data collected from the LSCTs according to Eqs 3 to 5, while the second method used the data collected from the strain gauges, according to Eqs 6 to 8 [13]. The total slippage between the GFRP and the UHPC can be determined by the summation of strain differences between adjacent strain gauges over the length of the bond. This value would then be comparable to the differential movement indicated by

Discussion and Analysis

FIG. 10—Distribution and variance of tension strength for different types of epoxy used for coarse silica sand bonding.

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TABLE 4—ANOVA F-test results for tension pull-out test specimens.

Source of Variation

SS

df

MS

F

P Value

Fcrit

Between groups

105342

2

52671

8.52

0.000827

3.23

Within groups

247253

40

6181

the LSCT readings, allowing for proper comparisons to be made between the

two methods. Method 1

£

II

<4

(3)

II

(4)

d ___ Me Mw

dave — 2

(5)

where:

1E, lw = the LSCT readings from the east and west sides, respectively (mm) and dave = the measured slip (mm).

Method 2

dE =

|-L 5

e{x)dx ffi Ei, E&Li 0 1

(6)

dw =

|-L 10

e{x)dx ffi У” ei WDLi 0 6

(7)

d dE + dw

dave — 2

(8)

where:

dE, dW = the integrated deformation on the east and west sides, respectively (mm),

ei, E, £i, w = the reading at strain gauge i on the east and west sides, respec­tively (ie),

DLi = the average centre-to-centre spacing between gauge i and the adjacent gauges i — 1 and i + 1 and,

dave = the average integrated deformation (mm).

The shear interface slippage behaviour exhibited for all of the specimens, determined using both the methods described in the section, are shown in Figs. 11, 12, and 13 for the specimens using epoxy types A, B, and C, respectively, at the bond interface. The shear interface slippage behaviour was shown for the

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Discussion and Analysis

FIG. 11—Shear interface slippage behaviour for double shear test specimens with epoxy type A at the bond interface.

 

Discussion and Analysis

FIG. 12—Shear interface slippage behaviour for double shear test specimens with epoxy type B at the bond interface.

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Discussion and Analysis

FIG. 13—Shear interface slippage behaviour for double shear test specimens with epoxy type C at the bond interface.

side that experienced failure, as indicated earlier in Table 1, using Eqs 3, 4, 6, and 7 where applicable. In the case of the specimens that used epoxy type A at the bond interface, where bond failure did not occur, the average slippage calcu­lated from Eqs 5 and 8 were used for analysis. Comparison between the two methods used to determine the shear slippage behaviour at the interface showed mixed findings and correlations, where the results determined using methods 1 and 2 were represented using darker and lighter lines, respectively. For epoxy type A, the trend exhibited by the three specimens in Fig. 11 showed moderate consistency within the results obtained from each of the two methods; however, when comparing the values obtained between the two methods, there were noticeable differences where significant divergence in the trend were noted when the applied load exceeded approximately 100 kN, which is equal to a bond shear strength of 1.11 MPa. In the case of the specimens that used epoxy type B at the bond interface, initial observations showed that extremely large discrep­ancies were present in Fig. 12 when comparing the results from the two meth­ods. More specifically, there were irregular portions in the curves, shown by the portions where the amount of slippage at the interface appeared to be decreas­ing with increased loading, which may have been caused by accidental slippage in the mounting apparatus of the LSCTs. Upon closer inspection, it can be seen that by ignoring the irregular portions, the characteristic features of both the darker and lighter curves (locations of dramatic slope changes) for each speci­men occurred at approximately the same load level. This demonstrates that con­sistent similarities were exhibited in the load-slippage behaviour of the specimens using epoxy type B. In Fig. 13 the shear interface slippage behaviours

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obtained using both methods for specimen C-2 were nearly identical. In the case of the other two specimens that used epoxy type C for bonding of the coarse silica sand aggregates, visible horizontal offsets were present though the distinctive features in the trend were seen to occur at the same load levels, similar to the observation made in regards to Fig. 12. Direct comparison of the load-slippage behaviour obtained through the use of the three different types of epoxy adhesives is shown in Fig. 14, which used the shear interface slippage curves determined using method 2 due to the fact that it provided more consist­ent and regular trends. In general, it was confirmed that the specimens that used epoxy types A and B showed better performance than the specimens that used epoxy type C.