PSI - Issue 44

Carlo Vienni et al. / Procedia Structural Integrity 44 (2023) 2262–2269 Vienni et al. / Structural Integrity Procedia 00 (2022) 000–000

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3.2. Results The results of shear-compression tests are represented in Fig. 4 in terms of capacity curves. In the graph, the comparison between the lateral response of the unreinforced wall URM_01 and the two reinforced panels RM_2_02 and RM_1_03 is shown. The capacity curves were drawn considering the load of the horizontal actuator (y-axis) and the drift of the panels along their effective height (x-axis): the drift was defined as the difference between the top displacement measured by Laser 1 and middle-height displacement measured by Laser 2. Even though tests were cyclic, the horizontal load – drift curves were obtained only for positive loading direction since the displacement of the contrast system was monitored only on one side of the wall (the side where the laser 2 is positioned, considered as positive direction). In Fig. 5 and 6 failure mechanisms of unreinforced and reinforced panels are shown. The unreinforced wall URM_01 collapsed due to the shear-sliding of the mortar joint placed at the middle height of the wall (Fig. 5a). After the beginning of the sliding, a progressive toe-crushing at the corners was observed. The two-sides reinforced panel RM_2_02 reached the peak load once the first diagonal cracks appeared in the reinforcement mortar. Then, the detachment at the masonry-to-mortar interface occurred and sliding between the masonry and the two CRM layers was observed. In the end, a complete failure of masonry was observed, including diagonal cracking and toe-crushing. The presence of steel connectors allowed to keep the integrity of the panel despite the significant damage. Therefore, the detachment of the mortar that occurred after the first cracking appearance has shown the low impact of connectors in the transfer mechanism of shear stresses between plaster layers and masonry; on the other hand, connectors were able to confine the wall and increase the ductility even after the opening of significant cracks. The one-sided reinforced panel RM_1_03 showed a quite similar behaviour: the lateral response was characterized by an almost linear behaviour until the first diagonal cracks appeared. Diagonal cracks were observed in both the plaster and the unreinforced side, see Fig. 6a and 6b. After the opening of the diagonal cracks, a detachment at the masonry-to-mortar interface was immediately observed and in the subsequent cycles, the progressive cracking and crushing of the masonry occurred. CRM mortar was almost unloaded after the detachment and no further cracks have been recorded on it. Table 4 summarizes the main properties of capacity curves, namely strength V U , stiffness K, and displacement capacity d u , showing the comparison among reinforced and unreinforced specimens in terms of amplification coefficient provided by CRM. The shear strength V U was evaluated as the peak load obtained in positive cycles. The stiffness was calculated as the secant stiffness at 0.70 V U , according to the common analysis procedure. The ultimate displacement d u was evaluated both as absolute value both as the ultimate drift corresponding to a strength reduction until 80% of the ultimate load. The application of reinforced plaster has led to an increase in shear strength and lateral stiffness. It is worth noting that the shear strength and stiffness increases in the one-sided reinforced panel are about half the corresponding values of the two-sided reinforced panel. The reinforcement system applied on two sides allowed to obtain a significant increase in the displacement capacity from about 15 mm (unreinforced panel) to 27 mm (reinforced panel). However, this increase was smaller considering the ultimate displacement corresponding to a 20% resistance degradation. In fact, in the case of the reinforced panel, once the peak load corresponding to the diagonal cracking and the detachment of the plaster was reached, a very fast degradation was observed due to masonry failure. Vice versa, the application of a single layer of CRM has led to a slight reduction of the ultimate displacement compared to the URM panel.

Table 4 - Results of shear-compression tests ID CRM k [kN/mm] 0.80 V U [kN]

V U [kN] 177,8 199,8

d u [mm]

d u_0.8 [mm]

α V [-]

α k [-]

α d [-]

α d_0.8 [-]

43,7 59,7

142,2 159,8

14,7 26,6

14,3 18,3

no

URM_01 RM_2_02 RM_1_03

-

-

-

-

1,12

1,37

1,81

1,28

2 sides

1 side

51,2

151,5

189,4

15,6

12,7

1,07

1,17

1,06

0,89