PSI - Issue 64

Alba Hyseni et al. / Procedia Structural Integrity 64 (2024) 246–253 Alba Hyseni / Structural Integrity Procedia 00 (2019) 000 – 000

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Table 1. mechanical properties of the masonry.

Average compressive strength f cm (MPa)

Average shear strength τ 0 (MPa)

Young's modulus E (MPa)

Shear modulus G (MPa)

Specific weight w (kN/m 3 )

7.20 ± 6%

0.90* 16* * Nominal value according to Italian National Design Guidelines, NTC (2018) and relative Circolare. 3360 ± 8% 1400*

2.4 Structural conception The bird’s eye view of the tower is illustrated in Fig. 3a. The steel tank is supported by four masonry columns with L-shaped cross-section. These are top constrained by a masonry vault as shown in Fig. 3b. In addition, four further columns with square cross-section (located side-by-side with the L-shaped) connect a set of curved stairs aimed to provide the access to the top room where the steel tank is installed (Fig. 3c). The latter has a 4.4 m, 7 m and 8 m for the height, the width and the length respectively. The roof is made up of a RC 3D-frame. A beam (having a 20x35 cm cross-section) is connected to the masonry walls all around the perimeter of the top room. A radial RC-beams structure runs from the middle point to the before mentioned beams. A chiasm of beams completes the 3D structural frame (see Fig. 3d and Fig. 2). a b c d

Fig. 3. masonry tank-tower: ( a) “bird’s eye view”, (b) vaulted ceiling and masonry arches, (c) steel tank and (d) RC top-frame.

2.5 Presence of existing reinforcement A group of four steel ties were installed in the past at the vault ’s level where the trust is maximum (see Fig. 2). 3. Creep law estimation Experimental investigations have been employed to interpret creep evolution in the recent past Anzani et al. (2009) and (2018); Mosoarca et al. (2020). It was observed that the time-dependent deformation of masonry under sustained load levels typically follows a three-stages curve as visible in Fig. 4a. The I-stage exhibits a visco-elastic behavior at decreasing strain-rate and almost reversible strain, while the II-stage is defined by a visco-plastic branch at a constant slope. Lastly, the III-stage is the so-called unstable branch , characterized by strain developing at increasing rate and ending with the masonry failure. At the scope of safeguarding the masonry structure, the II-stage creep is the most relevant because it represents the last chance to prevent the sudden failure. If the load level is low, the III-phase will not occur, and no failure is expected. In fact, I-phase corresponds to a stable and safe status not asking for engineer intervention. On the other side, if the masonry manifests cracks related to the III-stage, failure may occur easily if retrofitting is not applied properly and urgently.