Methodology for the Study of the Vulnerability of Historic Buildings: The Reconstruction of the Transformation Phases of the Church of the Abbey-Castle of Santo Stefano in Monopoli in Puglia (Italy)

The study presented here concerns an analysis of the structural vulnerability of the arm of the church of the Castello di Santo Stefano Abbey in Monopoli in Puglia (Italy). The ancient monument is located on a small “Peninsula” between two ancient natural harbors, 3 km from Monopoli and 5 km from the archaeological site of Egnazia. Studies on the abbey-castle, have revealed different construction and deconstruction phases relating to historical periods of the Roman age, late antique age, medieval age, modern and contemporary age. The castle is typically attributable to a closed courtyard with four arms. The last one, close to the wall on the port of Tramontana, was added at a contemporary time. The arm of the church is characterized by the crypt with opus reticulatum walls from the two surviving bays of the former Benedictine church, from the residential palace of the 18th century, and from the residential extensions of the 20th century. The north-east and north-west arms, born in the 16th century as defensive earth-filled walls with respective bulwarks (north-east pentagonal and north-west at the tip of a spear), were redeveloped between the 17th and 18th centuries into residential buildings with panoramic loggias and overlooking new ditches enclosed by high walled defenses. The study was conducted with non-invasive methods such as: thermographic surveys; archaeological survey; stratigraphic survey of the walls; stratigraphic survey of plants; photogrammetric survey; 3D returns; Morpho-typological survey of the building material making it possible to acquire data on degradation, on the historicization of instability, on the phases of “growth” of the 18th century and of stylistic “reconstructions” of the 19th century. The data acquired, compared with each other, documented: the deterioration and instability of the foundation wall structures (the crypt) and that of the elevated structures: surviving spans of the church and residential building. Alveolization of the building material, deformations, variations in the geometric shape, lack of resistance of the foundation walls due to the typological and qualitative characteristics of the material (opus reticulatum in soft tuff) with high porosity and problems of the church roof system