PSI - Issue 44

Mariateresa Guadagnuolo et al. / Procedia Structural Integrity 44 (2023) 878–885 M. Guadagnuolo et al. / Structural Integrity Procedia 00 (2022) 000–000

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1. Introduction Safety assessment and interventions design in existing buildings are typically affected by a different, not necessarily greater, degree of uncertainty than in newly designed buildings. The investigation phase to characterise masonry structures is a milestone in the so-called knowledge route indicated for existing buildings. The material analysis is fundamental to preparing the most suitable intervention techniques (Binda et al. 2001; Guadagnuolo et al. 2014; Frunzio et al. 2018; Boffill et al. 2020; Guadagnuolo and Faella 2020; Facconi et al. 2021). Whether destructive or weakly destructive, conducting extensive testing campaigns is often not feasible due to economic reasons or architectural and cultural constraints. Limiting the number of tests evaluating the possibility of using the results of investigation campaigns referred to coeval and similar buildings for materials and construction techniques is crucial (Boschi et al. 2021). Various investigation methodologies, partially destructive and non-destructive (Binda et al. 2007; Guadagnuolo et al. 2020; Pirchio et al. 2022), have been proposed to estimate masonry building strength. Among these, some allow the direct determination of the significant parameters, while others require analytical expressions or correlations, whose validity often has a limited field of application. Concerning partially destructive investigations, the most widespread methodology is based on the use of double flat jacks (ASTM C1196; ASTM C1197; ASTM D4729). The test should allow direct determination of strength and deformability of the masonry portion under investigation. However, due to the constraint conditions and the masonry texture, the flat jacks test often leads to values that are not fully representative of the actual strength of the masonry. That is probably due to the high intrinsic heterogeneity and anisotropy of the masonry structure. Performing an extended test campaign with more double flat jacks could represent a solution to the problem, but that does not happen due to the semi-destructive nature of the tests and their high cost. The path that provides further non-destructive investigation, including the visual classification methods, is often a preferred choice. Furthermore, in the case of a heterogeneous and potentially articulated construction, such as masonry, studies and investigations carried out on the local characteristics of individual panels cannot always directly represent the whole structure. Non-destructive tests, which are cheaper, more widely and quickly performed, indirectly provide masonry strength, but because numerous factors affect the behaviour (Epperson and Abrams 1989; Riva et al. 1998), their exclusive use may lead to unreliable results. Therefore, established practice is to replace a percentage of partially destructive tests with a more significant number, about three times as much, of non-destructive tests. This allows the results to be calibrated between the different types of tests, like sonic and penetrometer on the mortar (ASTM E494; UNI EN 12504-2). Regardless of the test performed, establishing the relationship among the results, the strength and elastic modulus of the masonry is the crucial step in the knowledge process. The Italian Technical Standards for Construction issued in 2018 (NTC 2018) provides a possible determination of the masonry mechanical parameters with the help of a correlation table. It includes a typological masonry classification in the first column and the related parameters in the following ones. It can be possible to use this table only by the first column to obtain mechanical parameters, so performing a simple typological characterisation. However, it can be possible to achieve a deeper evaluation by calculating the other mechanical parameters performing a linear interpolation of the table values corresponding to the compressive strength (f [N/mm 2 ]) value. In this field, many studies have been carried out to provide fully non-destructive methods for the mechanical classification of masonries. Several Authors (Pinto et al. 2021; D’Ayala et al. 2011; Fanale et al. 2017; Aminifar et al. 2022; Pirchio et al. 2022) present the possible use of the Masonry Quality Index (MQI) method (Borri et al. 2015) based on a simple visual inspection. This method provides a systematic approach to analysing masonry constructions through a qualitative analysis of some significant aspects, correlating the results to the mechanical parameters. However, the correlation functions between the MQI indexes and the mechanical parameters are not always fitted with that proposed by Borri et al. (2020). This paper investigates data related to yellow tuff masonry buildings located in Campania (South of Italy), for which both double flat jack tests and mortar penetrometer tests are available. The masonry quality with the MQI method is evaluated, the mechanical parameters of masonries without destructive tests is estimated using both the correlations given in (Borri et al. 2020) and the Italian Code NTC2018 (MIT 2018).