PSI - Issue 44

I. Boem et al. / Procedia Structural Integrity 44 (2023) 1260–1267 Boem I. and Gattesco N. / Structural Integrity Procedia 00 (2022) 000–000

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1. Introduction False ceilings made of thin, shallow masonry vaults are recurrent architectural elements in historical buildings; they are light structures supporting their own weight only, having decorative purposes in ecclesiastical or monumental buildings or also protective function for the above timber floor in production or service rooms. But seismic events evidenced their weakness in withstanding lateral loading, even when the relative displacement of the walls is effectively contrasted (e.g. by steel ties). Among the less invasive and more compatible strengthening strategies to improve the response of these elements in seismic prone areas (Niker, 2010; Girardello et al., 2013; Garmendia et al., 2015; Misseri et al.; 2019) there is the application of composite overlays made of a inorganic mortar matrix with un corrosive, fiber-based fabrics or grids embedded. These near-surface mounted techniques are suitable for application at the vault extrados (e.g. when valuable ceiling decorations need to be preserved) as well as at the intrados (e.g. when the access from the upper floor is not possible). The paper focused of two different types of fiber-reinforced inorganic matrices, classified as Composite Reinforced Mortar (CRM) and Fiber-Reinforced Cementitious Matrix (FRCM), that differ for the thickness of the mortar coating (30 mm in the former, 10 mm in the latter) and the type of the embedded reinforcement (pre-coated AR glass-fibers grids with 66x66 mm 2 pitch or dry carbon fabrics with 8x8 mm 2 yarns spacing, respectively). Generally, the choice of the strengthening technique relies on different application needs. Basically, the CRM reinforcement is simpler to install as, once the preformed composite grid has been positioned on the masonry surface, the mortar matrix can be simply applied / sprayed, as a common plaster; moreover, the typical irregularities of the historical masonry surface can be easily levelled within the mortar layer. The FRCM installation is more complex, as requires the application of a first thin layer of mortar, the careful on-site positioning and impregnation of the textile with an adhesive promoter and the application of a second thin mortar layer; but this results in a lower impact in terms of added mass in thin vaults, in respect to CRM. The performances of CRM and FRCM strengthened vaults are investigated in the paper experimentally and numerically, by comparing tests on full scale masonry vaults subjected to transversal loading. 2. Samples characteristics The experimental samples (Fig. 1) consisted in thin, shallow barrel vaults (thickness t = 55 mm) made of solid brick units arranged on a span s of 3900 mm and a width w of 770 mm; the radius was r = 2275 mm and the rise-radius ratio, f/r , resulted about 0.50. The vaults were built on solid brick masonry abutments (dimensions 380x770x460 mm 3 ), fixed to the ground. The solid brick clay units (55x125x250 mm 3 ) had an average compressive strength of 20.8 MPa and a flexural strength of 5.0 MPa; the masonry mortar (hydraulic lime / sand volume ratio = 1:3.5) had average compressive strength f c.b = 2.0 MPa, tensile strength f t,b = 0.2 MPa and Young modulus E b = 5.9 GPa.

Fig. 1. Geometry of the vault samples and general scheme of the testing apparatus.

Two different reinforcement techniques, were considered: CRM (suffix “C”) and FRCM (suffix “F”). For both the techniques, one vault sample with the reinforcement applied at the extrados (prefix “vRE”) and one at the intrados (prefix “vRI”) were tested; one unreinforced vault (prefix “vU”) was also considered, for comparison.