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

880

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2. Experimental tests Most of the masonry buildings in southern Italy were built using hand-squared tuff blocks and pozzolanic mortar. The compressive strength of the tuff may differ significantly according to the position of the quarry and the depth of extraction, the mortar, which is a mixture of ground lime and volcanic ash, one is medium-low (Autiero et al. 2021; Monaco et al. 2021). The double flat jack tests provide the parameters f m and E. The test consists of making two cuts in the masonry (parallel to each other and with varying distances made with a hydraulic saw with a circular diamond blade). Inside the cuts thus made, two flat jacks are inserted. These parallel jacks, which are suitably pressurised with the hydraulic system, apply a uniaxial stress state to the interposed masonry sample. A deformometer measures the resulting deformations in the masonry portion by pairs of dowel pins in a direction orthogonal and parallel to the insertion planes of the jacks. The test on the masonry is carried out up to a pressure above the local compressive state, limiting the maximum tension reached in the loading cycles to a value sufficiently below the breaking strain of the material (Fig. 1). The penetrometer test is a non-destructive test that enables the experimental estimation of the mechanical characteristics of mortar joints (Liberatore et al. 2016). The resistance that the mortar offers to the penetration of a needle of standardised steel determines the f mm parameter by using correlation curves (Felicetti and Gattesco 1998). It is possible to estimate the compressive strength of the mortar tested as a function of the depth of penetration of the needle after a predefined number of blows (Fig.1). Most of the data used for the database comes from monitoring reports provided by a company - Tecnolab s.r.l - operating in the consulting and structural diagnostics field. The results of numerous flat-jack tests (635) were previously analysed (Guadagnuolo et al. 2020). An average compressive strength of 1.96 MPa and an average elastic modulus of 1206 MPa were calculated. This paper analyses the experimental data referred to most representative buildings to compare with the NTC Code classification table and MQI method. To this purpose, ten masonries of tuff buildings with different textures and degradation have been selected (Fig. 1). For each masonry have been available the following information: • Compressive strength of the masonry (f m ) • Modulus of elasticity (E) • Compressive strength of the mortar (f mm ) Table 1 shows the experimental mechanical parameters for each analysed masonry. The masonry compressive strength ranges between 1.43 and 2.85 MPa with an average value of 2.11 MPa, while the E / f m ratio is between 368.42 (M9) and 769.95 (M7), with an average value of 581. The mortar compressive strength ranges between 1.47 and 3.36 MPa with an average value of 2.02 MPa.

Table 1. Experimental results

Masonry Compressive strength f m [MPa]

Mortar Compressive strength f mm [MPa]

Masonry Young modulus E [MPa]

Masonry

E/f m

M1 M2 M3 M4 M5 M6 M7 M8 M9

2.66 2.70 1.70 1.90 1.80 2.20 2.00 1.90 2.85 1.43

1869.10 1789.00 1121.70 744.60 1083.00 1127.90 1539.90 1046.00 1050.00 844.00

702.67 662.59 659.82 391.89 601.67 512.68 769.95 550.53 368.42 590.21

-

2.10 1.80 2.50 1.50 1.50 1.95 3.36 1.47 -

M10