PSI - Issue 44

Gianmarco de Felice et al. / Procedia Structural Integrity 44 (2023) 2122–2127 G. de Felice / Structural Integrity Procedia 00 (2022) 000 – 000

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The walls, on average 0.7-0.8 m thick, consist of tuff units and mortared joints. A clearly visible out-of-plumb, worthy of attention, is exhibited by the left (SW) lateral wall (Fig. 1d). An on-site inspection and a documentary investigation allowed to individuate the most vulnerable parts of the church requiring careful analysis, object of the present study, that is the façade (Fig. 1e) and a proportion of the SW lateral wall (Fig. 1d).

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Fig. 1. (a) The church of St. Maria Maggiore, (b) plan, (c) transversal section, (d) left nave with out of plumb external (SW) wall and façade (e).

3. The integrated methodology The proposed methodology is synthetically illustrated in Fig. 2. First the photogrammetric survey is carried out, to obtain the 3D model of the church through structure-from-motion software (Fig. 2a-c). The external part of the model is obtained through aero-photogrammetric survey, whereas a photogrammetric survey from the ground is performed to get the internal part. The photogrammetric process allows to obtain both the point cloud (Fig. 2a) and the textured meshed model (Fig. 2b), from which the orthophotos of the macro-elements of the structure under investigation are extracted (Fig. 2c). Orthophotos are imported in an edge detection Python code developed by the authors to detect blocks arrangement and to draw the block mesh (Fig. 2d), which is then imported in CAD for refinement (Fig. 2e). To date, the edge detection procedure is semi-automatic, since it is necessary to place markers on each block – Loverdos et al. (2021) – to make it possible to derive its shape and disposition within the macro-element under investigation. An enhancement of the procedure is currently under development, to allow for a completely automatic detection of masonry morphology. Afterwards, the mesh is imported in the DEM based code UDEC – Itasca (2019) – by an automatized open-source procedure, and the geometry of the DEM model is obtained (Fig. 2f). Material properties are therefore assigned to blocks - assumed as rigid - and to mortar joints, assumed to follow a Mohr Coulomb friction law with zero tensile strength and cohesion (due to mortar aging) (Fig. 2g). Finally, the pushover analysis is executed and the collapse mode (Fig. 2h) with the corresponding capacity curve (Fig. 2i) are obtained. The pushover analysis is performed following the automatic algorithm described in Gobbin et al. (2021), which allows to obtain both the ascending and the descending (softening) branch of the capacity curve. First, gravitational loads are applied. Then, horizontal forces proportional to mass are applied to each block. To gain the ascending branch,