PSI - Issue 44

Gabriele Guerrini et al. / Procedia Structural Integrity 44 (2023) 2214–2221 Gabriele Guerrini et al. / Structural Integrity Procedia 00 (2022) 000–000

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1. Introduction Jacketing has gained popularity for the seismic retrofit of masonry structures over the last four decades and is prompting research interest into innovative materials (Prota et al., 2006; Borri et al. 2011; De Felice et al., 2014; Gattesco et al., 2015; Carozzi et al., 2017; Del Zoppo et al., 2019; Türkmen et al., 2020; Guerrini et al., 2021a). The first solution was the so-called reinforced plaster: welded-wire steel meshes were embedded in cement-based mortar layers, applied to the surfaces of masonry walls with mechanical connectors. However, issues related to steel corrosion, cement compatibility with historical materials, and excessive weight and stiffness increase have become evident over time. Fiber-Reinforced Polymer (FRP) strips or sheets emerged as an alternative during the past twenty years because of their small thickness, resulting in minor weight and stiffness contributions. Nevertheless, they are currently discouraged for direct application to masonry surfaces because the epoxy matrix may compromise the preservation and durability of historical structures (Papanicolaou et al., 2008; Valluzzi et al., 2014). The evolution of the reinforced plaster concept has led to the Composite-Reinforced Mortar (CRM) system. The use of FRP meshes instead of steel reinforcement allows adopting smaller mortar thicknesses, because corrosion is of less concern, reducing additional weight and stiffness. Appropriate jacketing mortars (e.g., based on natural hydraulic lime) may ensure respect of authenticity in terms of materials and structural behavior, minimization and reversibility of the intervention, and physical/chemical compatibility with the original masonry substrate, thus enhancing the durability of the intervention and of the original structure. On the other hand, mortar-based composite materials such as Fabric-Reinforced Cementitious Matrices (FRCM), also known as Textile Reinforced Mortars (TRM), Cementitious Matrix Grids (CMG) or Inorganic Matrix Grids (IMG), have recently emerged as a promising solution. In this case, a flexible polymeric fabric is embedded within a thin layer of mortar, which results in thinner retrofit layers (up to 30 mm) compared to CRM (above 30 mm), thus minimizing interference with mass and stiffness. Finally, the application of fiber-reinforced mortars or concretes (FRC) without meshes can simplify and accelerate practical installations. For both FRCM and FRC systems, appropriate mortar mix designs should be considered as for CRM strengthening. Given the wide range of mortars, meshes, and connectors available on the market, diagonal compression tests were performed at the University of Pavia, Italy, on natural stone masonry specimens jacketed with 14 different combinations (Guerrini et al., 2021b). Two different solutions were then chosen for application to stone masonry piers, subjected to quasi-static cyclic shear-compression tests: a FRCM system with bidirectional Polyparaphenylene BenzobisOxazole (PBO) textiles, and a CRM retrofit with glass-FRP (GFRP) mesh. This paper focuses on the cyclic test outcomes in terms of pier failure mode and lateral displacement capacity enhancement. 2. Quasi-static cyclic shear-compression test 2.1. Specimen description The experimental program was conducted at the Department of Civil Engineering and Architecture of the University of Pavia, and at the EUCENTRE Foundation laboratories in Pavia, Italy. It aimed at assessing the effect of two different jacketing systems on the failure mode and lateral response enhancement of piers subjected to quasi static cyclic shear-compression tests. The campaign also included characterization tests on mortar samples from the masonry and the jacketing systems, vertical and diagonal compression tests on bare masonry specimens. Mechanical properties of stones, GFRP meshes, PBO textiles, helicoidal and PBO connectors were taken from technical sheets or official testing certificates. Two identical specimens, labeled P1 and P2, were built above reinforced concrete (RC) footings and simulated a pier bounded by two windows (Fig. 1). Thus, portions of the top and bottom spandrels were included. Timber lintels were provided above the openings, to facilitate hanging the top spandrels from the RC spreader beam, while the bottom spandrels were clamped to the footing during the test. The stones were roughly worked with a hammer to achieve dimensions between 100 mm and 300 mm. They were organized in two leaves with 5-to-20-mm-thick mortar layers forming irregular horizontal courses. No through stones were provided across the wall thickness, except for the opening edges. The block irregularities resulted in variable space between the two leaves, which was filled with mortar and stone scraps. The mean density of the masonry resulted equal to 1880 kg/m 3 .