PSI - Issue 11

P. Condoleo et al. / Procedia Structural Integrity 11 (2018) 290–297 P. Condoleo and A. Taliercio/ Structural Integrity Procedia 00 (2018) 000–000

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available nowadays allow the geometry of buildings to be reconstructed in detail taking the typical complex and stratified morphology of historical buildings into account. The transition from a very detailed geometric 3D model to a numerical model is often a cumbersome and tricky procedure. Apparently, it is necessary to simplify reality and, in particular, to carry out the subjective operation of discretizing the actual structure (Docci 1994). Whereas this procedure is almost spontaneous following a direct survey, it is somewhat more complex if advanced technologies are used. On the one hand, any geometric model needs to be simplified by eliminating details that are unnecessary from the structural point of view. On the other hand, construction techniques, materials, constructive faults and damages of the building should be known as accurately as possible, as they can significantly affect the structural behavior, although they may seem only minor issues. As far as the analysis of the damage conditions is concerned, two distinct objectives can be pursued. The first one consists in taking the “as built” state into account, i.e. neglecting cracks and geometric variations, to check whether the detected type of damage is compatible with the presumed original conditions of the building. Here, the first major issue related to the interpretation of the building conditions arises. Is any detected anomaly in the geometry a symptom of failure, or was the building simply built in that way? The answer requires an analysis to link the surveyed crack pattern to the deformation of the building, to understand the mechanisms by which it originated. The local building techniques and the historic period in which they were used, as well as the available historical documentation, have to be taken into account to try and explain existing faults (Giuffrè 2010). This information allows a “virtual” model (Siviero et al. 1997) of the undamaged building to be developed, in which the possible fault-inducing effects can be incorporated. The model can be validated by checking its ability in reproducing the existing crack pattern, originated by stresses exceeding the material strength. The second objective is to analyze the building in its current, damaged configuration, both to check the possibility of damage evolution and to assess the effectiveness of retrofitting techniques. Another element to be taken into account is the specific vulnerability of the building, which is affected by the construction technique, the transformations that have occurred over time, and the possible repairs (Doglioni and Mazzotti 2007). Examples of these factors, which induce discontinuities similarly to cracks, are flues, walls built at a later time and weakly connected to the rest of the building, walls resting on vaults, etc. Whereas the specific vulnerability has only a minor influence on the behavior of masonry structures subjected to gravity loads, it can play a detrimental role under horizontal actions (e.g. earthquakes, or thrusts exerted by arches and vaults). These factors must be incorporated in the virtual model, to assess their effects and to make the model as representative as possible of the actual building. In the present work, the above considerations will be applied to the assessment of a masonry farmhouse experiencing severe faults. 2. 2. Case study: a masonry farmhouse in Northern Italy 2.1. Description of the building The analyzed building is a two-storey farmhouse located in a hilly region in Northern Italy. The building has a relatively simple L-shaped plan. The complex is rather irregular, probably as a result of different construction phases (Fig. 1a). Only a part of the building has a basement. The southern side of the farmhouse adjoins other buildings. Most of the building consists of load-bearing walls in solid bricks and earthen mortar. The inner and outer walls are plastered (Fig. 2a), except for the north façade where brickwork is exposed (Fig. 2b). All the rooms have timber floors. In the oldest part of the house, the staircase is surmounted by a barrel vault, with two cross-vaults at both ends. The vault at the first floor is segmental. Also the entrance hall to the courtyard is topped by a barrel vault. A detailed analysis of the most ancient portion of the building allowed some geometric anomalies (specific vulnerabilities) to be highlighted: these “local weaknesses” might have fostered and affected the state of damage. The inner wall contains a flue that crosses the three floors, thereby reducing the wall section. Moreover, the openings are not aligned, thus leading to significant deviations of the stress path (Fig 1a). Another anomaly is in the entrance hall: by superposing the plans of the ground and of the first floor, it clearly stands out that a relatively thin wall of a bathroom (first floor) was built over the underlying vault (Fig. 1b); also the thickness of the wall