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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Each specimen has been at first subjected to 10 load cycles (R1 in Table 4) ranging from 0 to 0.86 kN, that is equal to 85% of the average value of the first peak load F1 obtained from monotonic tests (see Table 2). The diagrams in Figure 5 show that within this stage the slope of the loading and unloading branches almost coincide with that of monotonic tests; moreover, not significant residual deflections have been recorded and, at the end of the first loading-unloading stage, no significant cracks occurred in the specimens. The second group of 10 load cycles (R2) ranged from 0 to 1.57 kN, that is equal to 50% of the average value of the monotonic maximum load Fmax. Within the first load cycle, cracks occurred in the specimens close to the end of the constant (central) bending moment region. At the end of the first unloading phase, a residual deflection was recorded for all the specimens; the additional 9 loading-unloading curves of stage R2 almost coincide with the first one for 1T.0.C0.2 and 1T.0.C0.3 specimens, while increasing residual deflection was recorded for 1T.0.C0.1 specimen. Within the third stage (R3), 20 load cycles were applied to the specimens, ranging from 0 to 2.20 kN, equal to 70% of the average value of the maximum monotonic load Fmax. Additional cracks occurred in the specimens within the first load cycle, whilst almost no additional cracks occurred within the other 19 cycles. Nevertheless, for all the specimens the residual deflection increased at each cycle, indicating that damage grew within this stage. Note that the average slope of the loading-unloading curves remained almost constant within each stage (R1 to R3), but the average values decreased from R1 to R3. This suggests that damage of the specimens almost occurred just within the first loading cycle of each stage. Finally, load cycles ranging from 0 to 90%Fmax were applied to the specimens up to failure; within this stage (R4), specimens 1T.0.C0.1,2,3 failed respectively after 8, 3 and 14 cycles (see Table 4). Significant stiffness decrease and residual deflection increase were recorded: this indicates that damage and cracks considerably grew in the specimens within this stage. Anyway, similarly to monotonic tests, all the specimens failed because of compressive phenomenon in the masonry substrate (Table 5). It is noteworthy that load-displacement curves referring to monotonic tests envelop quite well the curves referring to cyclic tests.

Table 4. Number of load cycles applied to 1T.0.C0 specimens for each load range: R1 = 0-85%F1; R2 = 0-50%Fmax; R3 = 0-70%Fmax; R4 = 0-90%Fmax.

R1

R2

R3

R4

Specimen

0-0.86 kN

0-1.57 kN

0-2.20 kN

0-2.83 kN

1T.0.C0.1 1T.0.C0.2 1T.0.C0.3

10 10 10

10 10 10

20 20 20

8 3

14

Figure 5. Load-displacement diagrams obtained from monotonic and cyclic tests.