PSI - Issue 44

S. Monchetti et al. / Procedia Structural Integrity 44 (2023) 1988–1995 Silvia Monchetti et al. / Structural Integrity Procedia 00 (2022) 000–000

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Pisano. The five high relief panels and the decorative figures are carved in Carrara marble in a late Gothic style (Fig. 2C and Fig. 2D). The pulpit is supported by seven columns (Fig. 2D) that are connected to its base by a system of pointed arches (Fig. 2E). Four of these columns stand on white marble plinths at different heights, two of which are in the shape of a lion, a central one depicting an eagle, a griffin, and a winged lion, and a fourth with Adam in the guise of Altlante (Fig. 2). The pulpit is about 4 meters high and the diameter of the hexagon is about 2 meters. As is common with monuments, the history of this pulpit is as long as it is poorly documented. Around 1619 it was relocated, with the aim of bringing it closer to the faithful in accordance with the indications of the Council of Trent, to the middle of the nave on the left side of the church, where it can currently be admired. During the reassembly of the work, the vertical order of the panels was changed and the two lecterns were eliminated. These two lecterns are now in the Metropolitan Museum of New York and in the Bode-Museum of Berlin. The lectern currently placed on the pulpit from 2001, in the form of the Eagle of St John, is a copy. Restorations and structural interventions have taken placed over time, including, in the 19th century, structural work carried out with the insertion of iron brackets and the addition of stone in some areas where it was missing due to deterioration occurring over the time. Since 1947, the “Opificio delle pietre dure” has been involved in the periodic monitoring of the pulpit. As part of these efforts, in 2007, a series of investigations and studies were carried out, e.g., morphometric survey; analysis of the constituent materials (stone material, finishes and gilding applied on the marble, glass inlays, mortars for the bedding of the marble slabs); geological and geomechanical analyses to define the conditions of the foundations; endoscopic analyses; geophysical ultrasound surveys; georadar surveys, to verify any soil anomalies; gammagraphic survey on columns and arches above. The report of these activities and the analyses of the experimental tests results can be found in Altrovandi et al. (2011) where the authors do not exclude the possibility of a complete disassembly of the pulpit in order to overpass the structural criticisms found. Indeed, the analyses revealed signs of movements and repairs: the columns are slightly out of alignment and, in some cases, the joints between column and plinth or capital show signs of restoration work to compensate for this misalignment with the massive addition of molten lead to fill the joint areas. Furthermore, in the upper part, the iron pins inserted in the marble have oxidised by causing the widening of cracks and, in some cases, breaks in the marble. 2.2. 3D survey and monitoring system The periodic monitoring of an historical building, and the works of art inside, is one of the main tools necessary to promote a global strategy based on evaluation and containment of possible damages and degradation processes through periodic checks and minor maintenance. As part of the project CHARMING PISTOIA, it is possible to take advantage from experimental campaigns already carried out on the pulpit of Giovanni Pisano and the church of Sant’Andrea and to analyse the data from the currently active monitoring system.

Fig. 3: The computational model of the pulpit of Giovanni Pisano.