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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were performed. All specimens were cured under laboratory conditions for at least 28 days before testing. Experimental results of bond tests are shown in Table 3 in terms of average peak load F u_B , peak stress in the fibers σ u_B = F u_B /A f , and ultimate tensile stress on the interface τ u_B = F u_B /A b , where A b is the total surface of the bonded area. Failure always occurred due to a brittle detachment at the matrix-to-support interface.

Table 3. Results of single-lap shear bond tests. Average values and CoV in round brackets. Specimen F u_B [kN] σ u = F u_B /Ay [MPa] τ u = F u_B /A b [MPa] Specimen

τ u = F u_B /A b [MPa] 0,24 (13,5%)

σ u = F u_B /A y [MPa] 370 (13,5%)

F u_B [kN]

BT_X (CoV)

8,26

417 (11,3%)

0,23 (11,3%)

BT_Y (CoV)

8,80

3. Shear-compression tests 3.1. Description of specimens and test setup

The experimental study carried out in the present work concerned the study of the cyclic behavior of CRM reinforced brick masonry panels through shear-compression tests. For this purpose, three walls were built and tested at the Structures and Materials Testing Laboratory of the Department of Civil and Environmental Engineering of Florence. The panels had dimensions of 1000x1225x250 mm 3 and were equipped with a 50mm concrete layer at the base to simplify their movements. The first wall was kept unreinforced as a reference (URM_01), one wall was reinforced with two layers of CRM (RM_2_02), and the last with one layer only (RM_1_03). The CRM system was made by the application of the fiber grid to wall faces, the connection of the grid to masonry using five helical steel connectors, and finally by the application of the mortar with a thickness of about 30 mm per side. Masonry panels were cured for 28 days before the application of CRM and then for additional 28 days before testing. A sketch of unreinforced and reinforced panels is shown in Fig.2. The three panels were tested in shear-compression considering a cantilever static scheme with a free length of the wall equal to h eff = 720 mm and a compression level N = 350 kN. The test setup was characterized by a self-balanced steel frame structure. A representation of it is shown in Fig. 3. Three HE 300 B beams provided the base support of the panel (mark 1 in Figure 3). The compression load of 350 kN was applied through a vertical mechanical actuator and maintained constant during the whole test (mark 2). The vertical actuator was connected to the steel structure through two columns HE 240 B and two C-shaped beams. The horizontal displacement was applied through a horizontal actuator, with a maximum displacement capacity of ±75mm and maximum load capacity of 350 kN (mark 3). A HE 280 B beam was placed at the top section of the panel to uniformly apply the vertical load and to transfer the horizontal displacement (mark 4); the transfer of the horizontal force from the actuator to the wall was guaranteed by the presence of two L-shaped profiles welded to the top beam. To restrain lateral out-of-plane displacements of the panel, an adjustable restraint system was designed, consisting of two UPN 160 beams on which adjustable steel plates have been fixed and placed in contrast with the beam placed above the wall (mark 5). Teflon sheets were placed between the top beam and the lateral restraining system to avoid frictional resistance during the test. Regarding the static scheme, the test setup was designed to ensure a shear failure mechanism of masonry walls. For this purpose, the effective height of the panels was reduced by introducing a contrast system at the base: the restraint was built through two metal plates with dimensions 300x600x50 mm 3 (mark 6), and each of them was forced against the panel through two M24 bolts. The bolts were connected to two horizontal beams HE 320 B with a length of 2700mm and were preloaded before the beginning of each test (mark 7). A rubber sheet with dimensions 1000x250x20 mm 3 was placed above the panels, between the loading beam and the top face, to avoid stress concentrations, and, in the case of reinforced panels, to apply vertical compression only to the masonry panel without directly loading the CRM layers. The same condition was guaranteed at the base section of the specimens by the presence of the 50mm concrete layer.