PSI - Issue 11

Mariateresa Guadagnuolo et al. / Procedia Structural Integrity 11 (2018) 444–451 Author name / Structural Integrity Procedia 00 (2018) 000–000

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Methods adopted in restoration project, began with the analysis of the conservation state of the surfaces and of problems connected with weeds. Analysis included surface coats chemical characterization, by which, the best cleaning approach and the most compatible (suitable) materials to be used, were chosen. The use of specific products was leaded by the accurate advice of chemists, who are becoming always more advisor specialists in restoration techniques. Although the tower shows good structural conditions, its safety against potential future earthquakes is of primary importance. The main intervention fields were securing the elements damaged by the lightning, positioning of the recovered elements, verification of the bricks stricken by the lightning; verification and protection of tie rods and other metal elements; integration by envelope lines of the lost but reproducible portions, weeds removal and stones cleaning, building of a new gangway made of wood and metal, new fences to mark the bell tower surrounding area, a new electrical system, installation of a lightning rod. Those interventions were calibrated by in situ verification analysis and efficiency tests to keep under control the intervention result and its economic impact. Considering the degradation state of the "pietra di San Iorio" its petrographic and physical characteristics were studied to apply the correct washing pressure and to identify the coating allowing to unalterate the colours and improve its characteristics of resistance to corrosive agents. The interventions on the plasters aimed to preserve the matter and reintegrate it where necessary. Each intervention aimed at preserving the existing material, without altering its overall image in any way, nevertheless characterizing the "contemporary" aspect of the cultural heritage.

Fig. 4. The “Corpus Domini” bell tower after the restoration.

3. Seismic safety of the “Corpus Domini” Bell Tower

The assessment of safety, as well as the necessity and the suitability of eventual retrofits, has to be determined from the comparison of the structure capacity, evaluated as the result of qualitative and quantitative knowledge and analysis of the building, and the seismic action demand. This assessment can be performed by simplified methods, that are different from the specific ones used in the strengthening design. Safety index I S greater than 1 indicate structures able to withstand the required seismic forces, provided by the seismic code; on the contrary if I S is lesser than unity, the safety is lower than that prescribed (MIT, 2008;2011). According to the above briefly described procedure LV1 outlined in (MIT, 2011), by considering the geometric features of the “Corpus Domini” Bell Tower, the acceleration factors (f a ) of main portions were computed (Guadagnuolo et al., 2014a). These portions are the most representative in terms of geometries and openings; their plans are reported in Figure 3. Seismic safety was