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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formulations to design retrofitting interventions. Most of the works have been carried out using diagonal-compression tests. Gattesco and Boem (2015) carried out diagonal compression tests on different types of masonry obtaining a significant increase in terms of strength. Del Zoppo et al. (2019) studied the in-plane shear capacity of traditional reinforced plaster and CRM systems on tuff walls showing that the effectiveness of the reinforcement is mainly related to the tensile strength of the plaster mortar. D’Antino et al. (2019) analyzed the behavior of CRM reinforced brick masonry walls through diagonal compression tests, observing that the peak resistance is linked to the mortar tensile strength while the reinforcement grid provides an increase in terms of ultimate displacement. In Donnini et al. (2021) diagonal-compression tests were carried out on CRM reinforced brick and tuff masonry walls and an analytical formulation was proposed to calculate plaster contribution to the shear strength of reinforced panels. Besides several experimental studies based on the diagonal compression test, a few works were carried out using shear-compression tests. The shear-compression test is the reference experimental test to define the in-plane shear response of unreinforced masonry walls. During the test, piers are subject to a given compression load, maintained constant, and to an imposed lateral displacement. In most works reported in the literature, walls were subjected to either cantilever or fixed-fixed boundary conditions, and a horizontal cyclic loading history with one or more cycles per amplitude level was applied. In some cases, as in Vasconcelos and Lourenço (2009), the horizontal displacement was imposed monotonically until failure. Wilding et al. (2017) and Beyer et al. (2014) have shown that cyclic tests lead to slightly higher stiffness and significantly lower displacement capacity than monotonic tests, while shear strength appears to be almost insensitive to the loading protocol. The main result of shear-compression tests is the base shear - top displacement curve, from which several information on the seismic behavior of masonry walls can be obtained, namely stiffness, shear strength, and ultimate displacement. These tests also point out the different failure mechanisms affecting unreinforced walls, as observed in Magenes and Calvi (1997): specimens tested with a low compression level and high aspect-ratio exhibit a rocking behavior, overturning about wall corners; low aspect-ratio walls tested with medium compression level exhibit a shear failure mechanism characterized by a diagonal cracking (in case of irregular textural arrangement) or by shear sliding at mortar joints (in case of regular masonry arrangement); finally, specimens with very high compression ratio show a flexural failure related to toe-crushing, with damage concentrated at wall corners. A similar behavior was also observed in Orlando et al., (2016) using numerical simulations. Regarding reinforced walls, in Gattesco et al. (2013) an experimental study was carried out considering both shear compression and diagonal compression tests of CRM reinforced stone panels: from shear-compression tests, an increase in shear strength of V Reinf /V URM = 1.33 was obtained, significantly lower than the same masonry panels subject to diagonal compression (F Reinf /F URM = 4.00). This work deals with a CRM system composed of a glass fiber grid embedded in a lime mortar matrix with a thickness of 30mm and applied to brick masonry walls. A series of experimental tests were performed to define the mechanical properties of CRM components and brick masonry walls. Subsequently, three full-scale brick masonry walls were built: one of them was kept unreinforced as a reference, one was reinforced on both sides by the application of CRM and the last was reinforced on one side only. Quasi-static shear-compression tests were carried out to analyze reinforcement efficiency in terms of in-plane strength, stiffness, and displacement capacity. 2. Materials mechanical characterization 2.1. Brick masonry Masonry walls were built using clay bricks with dimensions of 230 x 120 x 55mm 3 and a commercial hydraulic lime-based mortar for the 10mm thick joints. Uniaxial compression tests were carried out on five bricks according to EN 772-1; an average compressive strength f b = 37 MPa was obtained. The compressive and flexural strengths of the mortar were evaluated on six prismatic specimens with dimensions of 40 x 40 x 160mm 3 according to UNI EN 1015 11, obtaining a compressive strength of f cm = 5.93 MPa (CoV 12.1%) and a flexural strength of f fm = 2.14 MPa (CoV 7.80%). Finally, compressive tests were carried out on three small masonry panels with dimensions of 230x115x400 mm 3 to evaluate the mechanical properties of masonry, which exhibited an average compressive strength of f c = 13.80 MPa and an average Young Modulus of E m = 3984 MPa.