PSI - Issue 44

Francesca Ferretti et al. / Procedia Structural Integrity 44 (2023) 2254–2261 Ferretti et al./ Structural Integrity Procedia 00 (2022) 000–000

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1. Introduction Masonry walls are load-bearing elements that can safely support vertical loads. The shear behavior of masonry walls, on the other hand, is more complex and involves a variety of factors (Calderini et al., 2009; Yardim & Lalaj, 2016), among which the quality of the constituent materials as well as the adhesion between mortar and bricks. In addition, because of the nature of masonry walls and the low tensile strength of the material, masonry behavior is very brittle. The primary goal of strengthening interventions on masonry buildings is to improve the behavior of the masonry structural elements. With this purpose, the use of composite materials, such as Fiber Reinforced Cementitious Matrix (FRCM) and Composite Reinforced Mortar (CRM), represent a very efficient solution (Del Zoppo et al., 2019; Incerti et al., 2019; Ferretti et al., 2021; Ferretti & Mazzotti, 2021). Inorganic matrices and high-strength fibers, such as steel, carbon, basalt, or glass, are combined to form FRCM and CRM composites (Gattesco & Boem, 2015; Marcari et al., 2017). Fiber grids, embedded inside the inorganic mortar matrix, are used as an externally bonded masonry member reinforcement. Tensile loads are carried by the fibers, whereas stress transmission between the fibers and the substrate is carried out by the inorganic matrix (D’Antino et al., 2019, 2020). However, FRCM and CRM systems are not applicable when the surface of the masonry should remain visible, i.e., in historical buildings. Therefore, other techniques should be adopted, such as the reinforced repointing technique (Casacci et al., 2019). The main objective of this research is to investigate the efficiency of different strengthening techniques, such as reinforced repointing combined with FRCM and CRM, applied on clay brick masonry panels subjected to diagonal compression tests. 2. Description of the experimental program The experimental campaign here presented involved conducting diagonal compression tests, in accordance with the ASTM E519 Standard, on four clay brick masonry panels (1300×1300×250 mm 3 ) with the objective of investigating the effectiveness of various types of reinforcement layouts, involving the use of reinforced repointing, Fiber Reinforced Cementitious Matrix (FRCM) and Composite Reinforced Mortar (CRM). The reinforced repointing technique consisted in the use of a continuous mesh made of galvanized Ultra High Tensile Strength Steel (UHTSS) strands positioned inside the horizontal and vertical mortar joints and fixed to the masonry panel through helicoidal AISI 316 stainless steel anchors. The FRCM system was composed by a lime based mortar matrix and a balanced glass grid, characterized by fiber equivalent thickness of 0.076 mm per direction, mesh size 30×30 mm and weight density equal to 400 g/m 2 . The CRM system was composed by a lime based mortar matrix and a preformed mesh in Glass Fiber Reinforced Polymer (GFRP), characterized by nominal bar section of 7.065 mm 2 , nominal bar diameter of 3 mm, mesh size of 66×66 mm and net weight of 380 g/m 2 .

2.1. Mechanical properties of the materials 2.1.1. Solid bricks

Solid clay bricks (120×250×55 mm 3 ) from the S. Marco furnace were used for the construction of the masonry panels. Some brick samples were cored both in the longitudinal (//) and in the transverse (  ) direction to determine their mechanical properties. Standard laboratory tests, such as uniaxial compressive test (EN 772-1), flexural test (EN 12390-5:2009) and tensile splitting test (EN 12390-6:2009) were performed. Average results are reported in Table 1.

Table 1. Brick mechanical properties. Type of brick

Compressive strength f c,b (MPa)

Flexural strength f fl,b (MPa)

Tensile strength f t,b (MPa)

23.9 ( // ) 18.7 (  )

4.2 ( // ) 3.1 (  )

San Marco Rosso Vivo

4.8