PSI - Issue 11

Mario Fagone et al. / Procedia Structural Integrity 11 (2018) 250–257 Author name / Structural Integrity Procedia 00 (2018) 000–000

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appear not very scattered being the coefficient of variation between 11 and 20% for the characteristic load values and between 10 to 21% for the stiffness values. First cracks in the specimens occurred at the end of the first linear branch, at a load level (F1) of about 33% of the maximum load (see Table 3); at P1 one or two “bending-type” fractures, involving both bricks and perpend joints, occurred close to the end of the constant (central) bending moment region of the specimens. After P1, the average slope of the load-displacement diagrams considerably decreases (K 2 /K 1 @ 38%): within the test stage corresponding to the second stroke of the interpolating load-displacement graph, cracks grow both in the masonry substrate and behind the CFRP reinforcement (a few millimeters below the CFRP sheet-substrate interface). Then, after P2, a third more scattered branch follows up to the specimen failure; note that the load level does not considerably vary between points P2 and P3: the average value of the ratio F2/Fmax and F3/Fmax is, in fact, about 90-92%. Within the third stage, cracks in the substrate mainly grew in the central portion of the specimen, close to the loading plate: it is apparent, from the crack pattern, that the stress distribution in the specimen was such that a compressed internal arch (within the thickness) occurred, for which the reinforcement acted as a chain. Failure of specimens always occurred because of compressive masonry failure (“MasF” in Table 2).

(a)

(b)

Figure 4. Monotonic tests: (a) load-displacement diagrams and (poly-)linear interpolations; (b) interpolations and characteristic points.

Table 2. Characteristic load values F1, F2 and Fmax, average slope of the first (K1) and second (K2) branches of the load displacement diagrams and failure modes occurred during the monotonic tests.

F 1

F 2

F max [N]

K 1

K 2

Specimen

Failure mode

[N]

[N]

[N/mm]

[N/mm]

1T.0.M.1 1T.0.M.2 1T.0.M.3

Mas-F Mas-F Mas-F mean

1013 1125 898

3326 3135 2223

3510 3389 2521

549 459 470

202 213 140

1012 11.24

2895 20.36

3140 17.18

493 9.99

185

1T.0.M

c.v. [%]

21.21

Table 3. Load and stiffness ratios.

Series

F 1 /F max [%]

F 2 /F max [%]

F 3 /F max [%]

K 2 /K 1 [%]

mean 32.55

c.v.

mean 91.81

c.v. 3.63

mean 90.47

c.v.

mean 37.69

c.v.

1T.0.M

10.50

11.34

22.10

4.2. Cyclic tests Specimens of 1T.0.C0 series were subjected to cyclic four-point bending tests: the considered load ranges and the number of load cycles applied to each specimen are reported in Table 4 whilst the obtained load-displacement diagrams are compared with the ones referring to monotonic tests in Figure 5.